| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
From the Department of Genetic Medicine and Development, University of Geneva Medical School and National Center of Competence in Research "Frontiers in Genetics", Geneva, Switzerland.
| Correspondence to: Dr Serge Nef, Department of Genetic Medicine and Development, University of Geneva Medical School, 1, rue Michel-Servet, CH 1211 Geneva 4, Switzerland (e-mail: Serge.Nef{at}unige.ch). |
| Received for publication April 23, 2009; accepted for publication September 15, 2009. |
Spermatogenesis is a strictly regulated process, at both the
transcriptional and the posttranscriptional level, which allows continuous
gamete production throughout adulthood. A novel mechanism of
posttranscriptional control mediated by microRNAs (miRNAs) has lately emerged
as an important regulator of spermatogenesis. miRNAs are endogenous, small,
noncoding RNAs produced through a multistep enzymatic process, which involves
the action of Dicer, an RNaseIII endonuclease. Here, we first present a short
overview of classic posttranscriptional control during spermatogenesis, and
then concentrate on recent findings that have unraveled the important role of
miRNAs in male reproductive function. Particular focus is given to the in vivo
role of miRNAs that has been demonstrated through the generation of Sertoli
cell–specific or germ cell–specific Dicer knockouts, as well as
the potential application of these findings in the treatment of human male
infertility and the development of male contraceptives. It is anticipated that
unraveling miRNA functions in the testis will further our understanding of the
regulatory mechanisms of mammalian spermatogenesis.
Key words: Dicer, Sertoli cells, germ cells, spermatogenesis
The nuclear condensation that occurs during spermiogenesis has long been of great interest, not only because it is essential for successful sperm production, but also because it involves fine mechanisms of posttranscriptional control. Before and during meiosis, histones are gradually replaced by testis-specific arginine-rich histone variants (H1t, TH2A, TH2B, TH3) (Meistrich et al, 1978). In fact, histones become hyperacetylated (Hazzouri et al, 2000; Marcon and Boissonneault, 2004), thereby facilitating nucleosome disassembly and histone displacement (Oliva and Mezquita, 1986). Histone variants are subsequently replaced by the basic transition proteins TP1 and TP2, which in their turn are replaced by protamines (PRMs), thus transforming the chromatin into a highly compact form (reviewed in Pradeepa and Rao, 2007).
Classic Posttranscriptional Control During Spermatogenesis
Spermatid chromatin compaction is incompatible with transcription;
therefore, any transcript essential for later stages of spermatogenesis must
be generated well in advance of its use and is thus under translational
control. In the mouse, transcription occurs all throughout spermatogonial
proliferation and meiosis, but ceases before the completion of spermiogenesis,
at the transition from round to elongating spermatids (reviewed in
Braun, 1998). In fact,
transcription occurs massively after meiosis; postmeiotic transcripts
accumulate in large amounts, become deadenylated, and are stored in the
spermatid cytoplasm for 4–5 days until their translation
(Kleene, 1993;
Braun, 1998). In mammalian
haploid germ cells (GCs), about two-thirds of all messenger RNAs (mRNAs) are
at least partially stored in translationally inactive free mRNA
ribonucleoprotein particles (Kleene,
1993; Schmidt et al,
1999).
Translational control involves protein repressors that bind either to the poly(A) tail or to other specific sequences in the 3' untranslated region (3'UTR) of an mRNA, although it now becomes clear that translational control can also be mediated by 5' untranslated region sequence elements (Yang et al, 2003). Two sequence elements in the 3'UTR of an mRNA are involved in translational control: the polyadenylation consensus motif (5'aauaaa3') and the cytoplasmic polyadenylation element (CPE; 5'uuuuuau3'), to which CPE-binding protein binds in order to promote polyadenylation (Hake et al, 1998).
Perhaps the best of numerous characterized examples of translational control during spermatogenesis is provided by the expression of Prm1 and Prm2, which encode for PRMs 1 and 2. Several proteins have been found to bind to their 3'UTR and control their expression, for example the 26-kd testis/brain RNA-binding protein (TB-RBP). TB-RBP interaction with the 3'UTR Y-box elements of Prm1 and Prm2 depends on phosphorylation and dimerization (Wu et al, 1998). In fact, TB-RBP not only controls translation of the Prm1 and Prm2 mRNAs, but also facilitates their movement from the nucleus to the cytoplasm, where they are temporarily stored (Morales et al, 1998). Importantly, although fertile, male mice lacking TB-RBP show decreased sperm count numbers and severe abnormalities within the seminiferous epithelium (Chennathukuzhi et al, 2003). Another Y-box protein binding to the 3'UTR and thus controlling translation of Prm1 is MSY4. Male mice in which Msy4 expression is extended beyond its normal window frame are completely infertile (Giorgini et al, 2002), thus demonstrating that repression of Prm1 translation must be relieved in a timely manner in elongating spermatids so as to successfully complete spermatogenesis.
Translational control has been a field of intense study for many years, and favors a classical dogma according to which binding of a protein on an mRNA is what controls its translation. However, several 3'UTR consensus sequence elements have been identified as mediators of translational repression, but for the moment, no specific protein binding to them has been found (Steger, 2001). The Z-box element is an example (Kwon and Hecht, 1991, 1993): it is a conserved 17-nt motif present in the 3'UTR of the Prm1 and Prm2 mRNAs that has the ability to mediate translational repression, yet no RNA-binding protein has been found to interact with it, thus leaving the question open as to what actually binds and mediates translational control of certain transcripts. Could it be a molecule other than a protein?
microRNAs: A Novel Mechanism of Posttranscriptional Control
Among the different classes of small RNAs, small interfering RNAs (siRNAs),
Piwi-interacting RNAs (piRNAs) and microRNAs (miRNAs) have emerged as
important regulators of development across eukaryotes (for a review see
Carthew and Sontheimer, 2009;
Ghildiyal and Zamore, 2009).
Fifteen years ago, a breakthrough discovery, that of the first miRNAs in
Caenorhabditis elegans (Lee et
al, 1993; Wightman et al,
1993) was about to change not only the classical dogmas of
posttranscriptional control, but, as we have witnessed in the last year, the
way we study reproductive biology as well.
miRNA Genomics: Genes and Biogenesis— miRNAs are single-stranded, noncoding small RNAs of approximately 22 nucleotides that have been found not only in plants and animals, but also in viruses (Pfeffer et al, 2004) and, more recently, in the unicellular algae Chlamydomonas reinhardtii (Molnar et al, 2007; Zhao et al, 2007); they function as posttranscriptional regulators of gene expression. miRNAs are endogenous molecules; they are encoded by miRNA genes, which are found either within introns, in which case they are transcribed as part of the gene in which they reside (Aravin et al, 2003; Lagos-Quintana et al, 2003; Lai et al, 2003; Lim et al, 2003), or intergenic regions, in which case they originate from independent transcriptional units (Lagos-Quintana et al, 2001; Lau et al, 2001; Lee and Ambros, 2001). Until now, 706, 547, and 286 miRNAs have been identified in human, mouse, and rat, respectively (Sanger Database, v13.0, March 2009; http://microRNA.sanger.ac.uk/sequences/).
In animals, miRNA genes are typically transcribed by polymerase II
(reviewed in Kim et al, 2009).
Their transcription produces a primary miRNA transcript (pri-miRNA), which
folds in a hairpin stem loop structure. The Microprocessor complex, which
contains Drosha, an RNaseIII endonuclease, and DGCR8 (in mammals) or Pasha (in
flies) (Han et al, 2004;
Landthaler et al, 2004),
cleaves the ends of both strands of the pri-miRNA and thus produces the
precursor miRNA (pre-miRNA), a stem-loop intermediate with a 5'
phosphate and 
2-nt 3' overhangs
(Lee et al, 2003).
Interestingly, Drosha cleavage occurs during transcription—independently
of the miRNA's gene location, intronic or intergenic—and in the case of
a miRNA gene embedded in an intron of a host gene, intron processing and
degradation occur before splicing of the nascent mRNA
(Morlando et al, 2008).
Alternatively, a pre-miRNA can be produced through splicing of a pre-mRNA,
during which an intron that precisely mimics the structural features of a
canonical pre-miRNA (the so called mirtron) is liberated
(Berezikov et al, 2007;
Okamura et al, 2007).
Pre-miRNAs are transported by exportin into the cytoplasm
(Yi et al, 2003;
Lund et al, 2004), where Dicer
(Dcr), another RNaseIII endonuclease, cleaves the hairpin structure at about 2
helical turns away from the stem loop
(Grishok et al, 2001;
Hutvagner et al, 2001;
Ketting et al, 2001). The
resulting miRNA:miRNA* duplex is then unwound by a helicase, and while the
miRNA* strand is degraded, the miRNA strand (the mature strand) is loaded onto
the RNA-induced silencing complex (RISC), which in addition to other proteins,
contains members of the Argonaute (AGO) protein family. The strand that gets
preferentially loaded on RISC is almost always the one with the
thermodynamically less stable 5' end
(Khvorova et al, 2003;
Schwarz et al, 2003). After
the assembly of RISC on the mature miRNA strand, the complex is tethered on an
mRNA target and, depending on the miRNA-mRNA sequence complementarity, induces
either translational repression or mRNA degradation. Of note, of the mammalian
Ago proteins (Ago1, Ago2, Ago3, and Ago4) that can be part of the RISC
complex, only Ago2 has the capacity to endonucleolytically cleave a target
mRNA ("Slicer" activity; Liu
et al, 2004b; Meister et al,
2004; Pillai et al,
2004), but all 4 are equally potent translational repressors
(Su et al, 2009).
miRNA Mechanisms of Function— Some studies have proposed that translational repression upon miRNA binding on an mRNA target occurs after the initiation step (Olsen and Ambros, 1999; Petersen et al, 2006), whereas others suggest that suppression occurs at the initiation step (Humphreys et al, 2005; Pillai et al, 2005; Wang et al, 2006; Mathonnet et al, 2007; Wakiyama et al, 2007). Of note, one study has proposed that miRNA-mediated translational repression can also occur during the elongation phase of translation, through proteolytic cleavage of the nascent polypeptide (Nottrott et al, 2006). mRNA degradation is the other possible effect upon miRNA binding. It was shown that, upon exogenous miRNA expression in mammalian cells, a large number of transcripts are down-regulated, and that the 3'UTRs of these transcripts are significantly enriched for miRNA binding sites (Lim et al, 2005). This study also showed that a far greater than expected number of transcripts are actually regulated by miRNAs. Additional studies later on confirmed the findings of Lim and colleagues: miRNAs in C elegans were found to induce degradation of their target mRNAs (Bagga et al, 2005), and in zebrafish, miR-430 was shown to be responsible for the clearance of maternal mRNAs during early embryogenesis (Giraldez et al, 2006).
In either case—translational repression or mRNA degradation—miRNAs obviously act as negative post-transcriptional regulators of gene expression. Recently, however, an elegant study presented data supporting an unexpected role for miRNAs as positive regulators: Vasudevan et al (2007) showed that although miRNAs repress translation of their targets in proliferating cells, they induce translational up-regulation upon cell cycle arrest, thus broadening the potential effect of miRNAs on gene expression and raising new, stimulating questions about the way miRNAs are—or should be—studied.
Taking out Dcr: miRNA Functions Unraveled
Given that Dcr plays a central role in the biogenesis of miRNAs, it quickly
became a great pole of attraction for all those interested in understanding
the biological functions of miRNAs. The first mouse Dcr knockout was
generated by Bernstein et al
(2003) in an effort to study
RNA interference mechanisms in mammals. Loss of DCR led to early embryonic
lethality (embryonic day [E]7.5), and was characterized by an almost complete
absence of embryonic stem cells, thus demonstrating the absolute necessity of
Dcr for murine embryonic development. Thereafter, numerous studies unraveled
an essential role for Dcr—and thus for miRNAs—in diverse
developmental processes (for example,
Harfe et al, 2005;
Harris et al, 2006;
Yi et al, 2006;
O'Rourke et al, 2007;
Kobayashi et al, 2008;
Suarez et al, 2008).
Not surprisingly, several groups turned their attention to the potential involvement of Dcr-dependent mechanisms in the regulation of the reproductive function. The first conditional Dcr knockout in the reproductive tract was done in mouse oocytes; 2 studies showed that although Dcr is dispensable for oocyte growth and development, it is essential for meiosis of the female germline. Deletion of Dcr in mouse oocytes results in an arrest of meiosis I, spindle disorganization, and chromosome congression defects. In addition, abnormally high levels of transposon transcripts are found in Dcr-depleted oocytes, thus suggesting that Dcr might somehow protect oocytes from the abnormal activity of transposable elements (Murchison et al, 2007; Tang et al, 2007). The role of DCR in the somatic compartment of the female reproductive tract was also studied; Dcr was specifically inactivated in the mesenchyme of developing Müllerian ducts and in ovarian granulosa cells and led to infertility because of diverse reproductive defects such as reduced ovulation rates, smaller oviduct and uterine horn size, appearance of bilateral oviductal cysts harboring unfertilized degenerate oocytes, and adenomyosis (Nagaraja et al, 2008; Gonzalez and Behringer, 2009).
miRNAs in the Testis: A New Era for Male Fertility
miRNAs were first cloned from the testis only a few years ago, in an effort
undertaken by several groups to establish techniques reliable for genome-wide
miRNA profiling (Barad et al,
2004; Liu et al,
2004a). Shortly afterwards, a more detailed analysis of the
testicular miRNAome reported that a number of miRNAs are differentially
expressed during testicular development
(Yu et al, 2005). The same
study also presented evidence for in vitro targeting of the Tp2 mRNA
by a testicular miRNA, miR-122a. However, the first physical evidence for the
potential involvement of the miRNA pathway in the regulation of male GC
development came when Kotaja et al
(2006) reported that DCR and
other components of the miRNA pathway, namely Ago2, Ago3, and testis-expressed
miRNAs (miR-21, let-7a, miR-122a), localize in the chromatoid body of male
GCs, from where they might control postmeiotic GC differentiation. Another
elegant study discussing the potential involvement of miRNAs in
posttranscriptional regulation in the testis reported that the miR-17-92
cluster is activated upon c-Myc expression and eventually leads to
the translational repression of E2F1, thereby preventing apoptosis during
meiotic recombination (Novotny et al,
2007). Two studies published shortly afterwards reported the miRNA
profile of the murine testis using either microarrays
(Yan et al, 2007) or cloning
analysis (Ro et al, 2007); in
the first study, whole testis was used as starting material, whereas in the
second, purified spermatogenic cells were used. Later on, another study
described the expression patterns of several members of the miRNA pathway in
the testis; Dcr, Drosha, Ago1, Ago2, Ago3, and Ago4 are all expressed in
pachytene spermatocytes, round and elongated spermatids, and Sertoli cells
(Gonzalez-Gonzalez et al,
2008). Shortly afterwards, in an effort to understand the
mechanism of meiotic gene silencing, Marcon et al
(2008) showed that miRNAs
localize not only to the chromosome cores, the telomeres, and the XY body of
spermatocytes, but also to the nucleolus of Sertoli cells. Another interesting
study recently reported that about 86% of X-linked miRNAs actually escape
meiotic sex chromosome inactivation (MSCI) during spermatogenesis: the study
showed that although transcriptional silencing of genes on chromosomes X and Y
occurs in mid- to late pachytene spermatocytes, most of the miRNA genes
located on chromosome X are de novo transcribed and processed at this stage,
thus suggesting either that they are involved themselves in MSCI or that they
are essential for posttranscriptional control of autosomal mRNAs during late
meiosis and early postmeiosis (Song et al,
2009).
Two groups described an in vivo model that studies the involvement of
miRNAs in spermatogenesis. Mice harboring 2 floxed Dcr alleles were mated with
primordial germ cell (PGC)-specific, Cre recombinase–expressing
(TNAP-Cre) mice, so as to generate animals in which Dcr is absent in germ
cells; loss of Dcr in the germ lineage of the testis was found to
result in defective PGC proliferation and eventual late adult infertility due
to spermatogenic arrest probably caused by defective proliferation and/or
differentiation of spermatogonia. Interestingly though, no defects were seen
when, instead of Dcr, Ago2 was deleted in germ cells, suggesting that
Dcr-knockout defects are independent of Ago2
(Hayashi et al, 2008).
Slightly different results were obtained in the study of Maatouk et al
(2008), who, using the same
Cre expressing transgenic mouse, found that males lacking Dcr in germ cells
were subfertile because of both a defect in the transition from round to
elongating spermatids and production of sperm with abnormal motility. The
results of both studies should be interpreted with caution because the
TNAP-Cre transgenic mouse does not seem to be fully penetrant (only 50%
of germ cells express Cre), nor to be specific uniquely to germ cells. It
should also be noted that because the expression of TNAP-Cre begins as early
as E10 (Lomeli et al, 2000),
it is difficult to understand how and when exactly spermatogenesis is affected
in the adult. The primary effects appear in the PGC population, and,
inevitably, the defect is carried on to adult germ cells; however, it is not
possible to measure the importance of miRNAs in adult germ cells; a postnatal
germ cell–specific deletion of Dcr would be required to assess this.
Given the essential role of Sertoli cells in spermatogenesis, we addressed the possibility of miRNA-mediated posttranscriptional control in this compartment of the testis, and provided in vivo evidence for the absolute requirement of Sertoli cell Dcr for the normal occurrence of spermatogenesis (Papaioannou et al, 2009). We showed that selective ablation of Dcr in Sertoli cells leads to infertility due to complete absence of spermatozoa and progressive testicular degeneration. The first morphological alterations appeared already at postnatal day 5 and were correlated with a severe impairment of the prepubertal spermatogenic wave because of defective Sertoli cell maturation and incapacity to properly support meiosis and spermiogenesis. An initial increase in SC proliferation was followed by massive Sertoli cell and germ cell apoptosis in prepubertal testes. Importantly, we found several key genes such as Gdnf, Kitl, Man2a2, and Serpina5, all known to be essential for spermatogenesis, to be significantly down-regulated in neonatal testes lacking Dcr in Sertoli cells. We hypothesized that this down-regulation could account—at least partially—for the numerous spermatogenic defects we observe; however, we do not neglect all those genes that were found to be upregulated because it is most likely to find among them direct RNA targets.
A Novel Class of Small RNAs in the Testis— We should note here that a new, male GC–specific class of small RNAs called piRNAs has recently been discovered (Aravin et al, 2006; Girard et al, 2006; Grivna et al, 2006; Watanabe et al, 2006), although for the moment their biogenesis is thought to be DCR independent (Vagin et al, 2006; Houwing et al, 2007). piRNAs are slightly bigger in size than miRNAs (26–31 nt), and 2 distinct groups have been identified: the first includes prepachytene-expressed piRNAs, which derive from repeat- and transposon-rich clusters and are associated with MIWI and MIWI2, 2 members of the AGO protein family (Aravin et al, 2007, 2008; Kuramochi-Miyagawa et al, 2008), and the second includes an extremely abundant group of pachytene-expressed piRNAs associated with MILI and MIWI (Girard et al, 2006; Aravin et al, 2007, 2008). Most piRNAs correspond to intergenic repetitive sequences including retrotransposons, and are thus thought to have a role in the silencing of selfish genetic elements; in favor of this hypothesis is the finding that MIWI and MIWI2 are essential for the repression of male GC transposons through de novo DNA methylation (Aravin et al, 2007, 2008; Carmell et al, 2007; Kuramochi-Miyagawa et al, 2008). The abundant presence of piRNAs in male GCs strongly suggests that they might play key roles in the regulation of spermatogenesis; in favor of this notion is the fact that loss of both Mili and Miwi leads to infertility. Spermatogenesis in Mili–/– mice is blocked at the early prophase of meiosis I, probably at the zygotene or pachytene stage, and sperm production is therefore almost completely absent (Kuramochi-Miyagawa et al, 2004), whereas in Miwi–/– males spermatogenesis is blocked at the round spermatid stage, and neither chromatin condensation nor spermatid elongation occur (Deng and Lin, 2002).
Conclusions and Perspectives
The discovery of miRNAs has inevitably had its impact on the field of
reproduction; reproductive biology is slowly entering into a new era, which
demands a thorough revision of the current theories, so as to complement them
with the most recent findings from RNA biology. Novel essential roles played
by the Dcr-dependent pathway in the male reproductive function have been
revealed. It is now clear that a global loss of miRNAs, whether in the
supporting or the germ lineage of the testis, has detrimental effects on male
fertility and, as such, should be taken into consideration when discussing
about treatment of male infertility or, on the opposite side, male
contraception. Surely, more detailed analyses at the molecular level are
required in order to identify individual miRNAs with key roles during
spermatogenesis: the need to generate knockouts for individual miRNAs now
seems evident. This will allow us to identify their target genes and thus to
understand in depth how the process of spermatogenesis is controlled by the
miRNA machinery. Certainly, the functional redundancy among miRNAs will not
make the task easy; however, the first attempts have opened new promising
routes and will soon deliver their fruit.
Acknowledgments
We apologize to other scientific colleagues whose work could not be cited due to space limitations.
Footnotes
Supported by the NCCR "Frontiers in Genetics" graduate school program (M.D.P.); Swiss National Science Foundation grant 3100A0-119862 (S.N.), the Prof Dr Max Cloëtta Foundation (S.N.), and the Société Académique de Genève (S.N.).
References
Aravin A, Gaidatzis D, Pfeffer S, Lagos-Quintana M, Landgraf P, Iovino N, Morris P, Brownstein MJ, Kuramochi-Miyagawa S, Nakano T, Chien M, Russo JJ, Ju J, Sheridan R, Sander C, Zavolan M, Tuschl T. A novel class of small RNAs bind to MILI protein in mouse testes. Nature. 2006;442: 203 –207.[Medline]
Aravin AA, Lagos-Quintana M, Yalcin A, Zavolan M, Marks D, Snyder B, Gaasterland T, Meyer J, Tuschl T. The small RNA profile during Drosophila melanogaster development. Dev Cell. 2003;5: 337 –350.[CrossRef][Medline]
Aravin AA, Sachidanandam R, Bourc'his D, Schaefer C, Pezic D, Toth KF, Bestor T, Hannon GJ. A piRNA pathway primed by individual transposons is linked to de novo DNA methylation in mice. Mol Cell. 2008; 31: 785 –799.[CrossRef][Medline]
Aravin AA, Sachidanandam R, Girard A, Fejes-Toth K, Hannon GJ.
Developmentally regulated piRNA clusters implicate MILI in transposon control.
Science. 2007;316: 744
–747.
Bagga S, Bracht J, Hunter S, Massirer K, Holtz J, Eachus R, Pasquinelli AE. Regulation by let-7 and lin-4 miRNAs results in target mRNA degradation. Cell. 2005; 122: 553 –563.[CrossRef][Medline]
Barad O, Meiri E, Avniel A, Aharonov R, Barzilai A, Bentwich I,
Einav U, Gilad S, Hurban P, Karov Y, Lobenhofer EK, Sharon E, Shiboleth YM,
Shtutman M, Bentwich Z, Einat P. MicroRNA expression detected by
oligonucleotide microarrays: system establishment and expression profiling in
human tissues. Genome Res. 2004; 14: 2486
–2494.
Berezikov E, Chung WJ, Willis J, Cuppen E, Lai EC. Mammalian mirtron genes. Mol Cell. 2007; 28: 328 –336.[CrossRef][Medline]
Bernstein E, Kim SY, Carmell MA, Murchison EP, Alcorn H, Li MZ, Mills AA, Elledge SJ, Anderson KV, Hannon GJ. Dicer is essential for mouse development. Nat Genet. 2003; 35: 215 –217.[CrossRef][Medline]
Braun RE. Post-transcriptional control of gene expression during spermatogenesis. Semin Cell Dev Biol. 1998; 9: 483 –489.[CrossRef][Medline]
Carmell MA, Girard A, van de Kant HJ, Bourc'his D, Bestor TH, de Rooij DG, Hannon GJ. MIWI2 is essential for spermatogenesis and repression of transposons in the mouse male germline. Dev Cell. 2007; 12: 503 –514.[CrossRef][Medline]
Carthew RW, Sontheimer EJ. Origins and mechanisms of miRNAs and siRNAs. Cell. 2009; 136: 642 –655.[CrossRef][Medline]
Chennathukuzhi V, Stein JM, Abel T, Donlon S, Yang S, Miller JP,
Allman DM, Simmons RA, Hecht NB. Mice deficient for testis-brain RNA-binding
protein exhibit a coordinate loss of TRAX, reduced fertility, altered gene
expression in the brain, and behavioral changes. Mol Cell
Biol. 2003;23: 6419
–6434.
Deng W, Lin H. miwi, a murine homolog of piwi, encodes a cytoplasmic protein essential for spermatogenesis. Dev Cell. 2002;2: 819 –830.[CrossRef][Medline]
Ghildiyal M, Zamore PD. Small silencing RNAs: an expanding universe. Nat Rev Genet. 2009; 10: 94 –108.[CrossRef][Medline]
Giorgini F, Davies HG, Braun RE. Translational repression by MSY4
inhibits spermatid differentiation in mice.
Development. 2002; 129: 3669
–3679.
Giraldez AJ, Mishima Y, Rihel J, Grocock RJ, Van Dongen S, Inoue K,
Enright AJ, Schier AF. Zebrafish MiR-430 promotes deadenylation and clearance
of maternal mRNAs. Science. 2006; 312: 75
–79.
Girard A, Sachidanandam R, Hannon GJ, Carmell MA. A germline-specific class of small RNAs binds mammalian Piwi proteins. Nature. 2006;442: 199 –202.[Medline]
Gonzalez G, Behringer RR. Dicer is required for female reproductive tract development and fertility in the mouse. Mol Reprod Dev. 2009;76: 678 –688.[CrossRef][Medline]
Gonzalez-Gonzalez E, Lopez-Casas PP, del Mazo J. The expression patterns of genes involved in the RNAi pathways are tissue-dependent and differ in the germ and somatic cells of mouse testis. Biochim Biophys Acta. 2008;1779: 306 –311.[Medline]
Grishok A, Pasquinelli AE, Conte D, Li N, Parrish S, Ha I, Baillie DL, Fire A, Ruvkun G, Mello CC. Genes and mechanisms related to RNA interference regulate expression of the small temporal RNAs that control C. elegans developmental timing. Cell. 2001; 106: 23 –34.[CrossRef][Medline]
Grivna ST, Beyret E, Wang Z, Lin H. A novel class of small RNAs in
mouse spermatogenic cells. Genes Dev. 2006; 20: 1709
–1714.
Hake LE, Mendez R, Richter JD. Specificity of RNA binding by CPEB:
requirement for RNA recognition motifs and a novel zinc finger. Mol
Cell Biol. 1998;18: 685
–693.
Han J, Lee Y, Yeom KH, Kim YK, Jin H, Kim VN. The Drosha-DGCR8
complex in primary microRNA processing. Genes Dev. 2004; 18: 3016
–3027.
Harfe BD, McManus MT, Mansfield JH, Hornstein E, Tabin CJ. The
RNaseIII enzyme Dicer is required for morphogenesis but not patterning of the
vertebrate limb. Proc Natl Acad Sci U S A. 2005; 102: 10898
–10903.
Harris KS, Zhang Z, McManus MT, Harfe BD, Sun X. Dicer function is
essential for lung epithelium morphogenesis. Proc Natl Acad Sci U S
A. 2006;103: 2208
–2213.
Hayashi K, Chuva de Sousa Lopes SM, Kaneda M, Tang F, Hajkova P, Lao K, O'Carroll D, Das PP, Tarakhovsky A, Miska EA, Surani MA. MicroRNA biogenesis is required for mouse primordial germ cell development and spermatogenesis. PLoS ONE. 2008; 3: e1738 .[CrossRef][Medline]
Hazzouri M, Rousseaux S, Mongelard F, Usson Y, Pelletier R, Faure AK, Vourc'h C, Sele B. Genome organization in the human sperm nucleus studied by FISH and confocal microscopy. Mol Reprod Dev. 2000; 55: 307 –315.[CrossRef][Medline]
Houwing S, Kamminga LM, Berezikov E, Cronembold D, Girard A, van den Elst H, Filippov DV, Blaser H, Raz E, Moens CB, Plasterk RH, Hannon GJ, Draper BW, Ketting RF. A role for Piwi and piRNAs in germ cell maintenance and transposon silencing in zebrafish. Cell. 2007; 129: 69 –82.[CrossRef][Medline]
Humphreys DT, Westman BJ, Martin DI, Preiss T. MicroRNAs control
translation initiation by inhibiting eukaryotic initiation factor 4E/cap and
poly(A) tail function. Proc Natl Acad Sci U S A. 2005; 102: 16961
–16966.
Hutvagner G, McLachlan J, Pasquinelli AE, Balint E, Tuschl T,
Zamore PD. A cellular function for the RNA-interference enzyme Dicer in the
maturation of the let-7 small temporal RNA. Science. 2001; 293: 834
–838.
Ketting RF, Fischer SE, Bernstein E, Sijen T, Hannon GJ, Plasterk
RH. Dicer functions in RNA interference and in synthesis of small RNA involved
in developmental timing in C. elegans. Genes
Dev. 2001;15: 2654
–2659.
Khvorova A, Reynolds A, Jayasena SD. Functional siRNAs and miRNAs exhibit strand bias. Cell. 2003; 115: 209 –216.[CrossRef][Medline]
Kim VN, Han J, Siomi MC. Biogenesis of small RNAs in animals. Nat Rev Mol Cell Biol. 2009; 10: 126 –139.[CrossRef][Medline]
Kleene KC. Multiple controls over the efficiency of translation of the mRNAs encoding transition proteins, protamines, and the mitochondrial capsule selenoprotein in late spermatids in mice. Dev Biol. 1993;159: 720 –731.[CrossRef][Medline]
Kobayashi T, Lu J, Cobb BS, Rodda SJ, McMahon AP, Schipani E,
Merkenschlager M, Kronenberg HM. Dicer-dependent pathways regulate chondrocyte
proliferation and differentiation. Proc Natl Acad Sci U S
A. 2008;105: 1949
–1954.
Kotaja N, Bhattacharyya SN, Jaskiewicz L, Kimmins S, Parvinen M,
Filipowicz W, Sassone-Corsi P. The chromatoid body of male germ cells:
similarity with processing bodies and presence of Dicer and microRNA pathway
components. Proc Natl Acad Sci U S A. 2006; 103: 2647
–2652.
Kuramochi-Miyagawa S, Kimura T, Ijiri TW, Isobe T, Asada N, Fujita
Y, Ikawa M, Iwai N, Okabe M, Deng W, Lin H, Matsuda Y, Nakano T. Mili, a
mammalian member of piwi family gene, is essential for spermatogenesis.
Development. 2004; 131: 839
–849.
Kuramochi-Miyagawa S, Watanabe T, Gotoh K, Totoki Y, Toyoda A,
Ikawa M, Asada N, Kojima K, Yamaguchi Y, Ijiri TW, Hata K, Li E, Matsuda Y,
Kimura T, Okabe M, Sakaki Y, Sasaki H, Nakano T. DNA methylation of
retrotransposon genes is regulated by Piwi family members MILI and MIWI2 in
murine fetal testes. Genes Dev. 2008; 22: 908
–917.
Kwon YK, Hecht NB. Cytoplasmic protein binding to highly conserved
sequences in the 3' untranslated region of mouse protamine 2 mRNA, a
translationally regulated transcript of male germ cells. Proc Natl
Acad Sci U S A. 1991;88: 3584
–3588.
Kwon YK, Hecht NB. Binding of a phosphoprotein to the 3'
untranslated region of the mouse protamine 2 mRNA temporally represses its
translation. Mol Cell Biol. 1993; 13: 6547
–6557.
Lagos-Quintana M, Rauhut R, Lendeckel W, Tuschl T. Identification
of novel genes coding for small expressed RNAs.
Science. 2001;294: 853
–858.
Lagos-Quintana M, Rauhut R, Meyer J, Borkhardt A, Tuschl T. New
microRNAs from mouse and human. RNA. 2003; 9: 175
–179.
Lai EC, Tomancak P, Williams RW, Rubin GM. Computational identification of Drosophila microRNA genes. Genome Biol. 2003;4: R42 .[CrossRef][Medline]
Landthaler M, Yalcin A, Tuschl T. The human DiGeorge syndrome critical region gene 8 and Its D. melanogaster homolog are required for miRNA biogenesis. Curr Biol. 2004; 14: 2162 –2167.[CrossRef][Medline]
Lau NC, Lim LP, Weinstein EG, Bartel DP. An abundant class of tiny
RNAs with probable regulatory roles in Caenorhabditis elegans.
Science. 2001;294: 858
–862.
Lee RC, Ambros V. An extensive class of small RNAs in
Caenorhabditis elegans. Science. 2001; 294: 862
–864.
Lee RC, Feinbaum RL, Ambros V. The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14. Cell. 1993; 75: 843 –854.[CrossRef][Medline]
Lee Y, Ahn C, Han J, Choi H, Kim J, Yim J, Lee J, Provost P, Radmark O, Kim S, Kim VN. The nuclear RNase III Drosha initiates microRNA processing. Nature. 2003; 425: 415 –419.[CrossRef][Medline]
Lim LP, Lau NC, Garrett-Engele P, Grimson A, Schelter JM, Castle J, Bartel DP, Linsley PS, Johnson JM. Microarray analysis shows that some microRNAs downregulate large numbers of target mRNAs. Nature. 2005;433: 769 –773.[CrossRef][Medline]
Lim LP, Lau NC, Weinstein EG, Abdelhakim A, Yekta S, Rhoades MW,
Burge CB, Bartel DP. The microRNAs of Caenorhabditis elegans.
Genes Dev. 2003; 17: 991
–1008.
Liu CG, Calin GA, Meloon B, Gamliel N, Sevignani C, Ferracin M,
Dumitru CD, Shimizu M, Zupo S, Dono M, Alder H, Bullrich F, Negrini M, Croce
CM. An oligonucleotide microchip for genome-wide microRNA profiling in human
and mouse tissues. Proc Natl Acad Sci U S A. 2004a; 101: 9740
–9744.
Liu J, Carmell MA, Rivas FV, Marsden CG, Thomson JM, Song JJ,
Hammond SM, Joshua-Tor L, Hannon GJ. Argonaute2 is the catalytic engine of
mammalian RNAi. Science. 2004b; 305: 1437
–1441.
Lomeli H, Ramos-Mejia V, Gertsenstein M, Lobe CG, Nagy A. Targeted insertion of Cre recombinase into the TNAP gene: excision in primordial germ cells. Genesis. 2000; 26: 116 –117.[CrossRef][Medline]
Lund E, Guttinger S, Calado A, Dahlberg JE, Kutay U. Nuclear export
of microRNA precursors. Science. 2004; 303: 95
–98.
Maatouk DM, Loveland KL, McManus MT, Moore K, Harfe BD. Dicer1 is
required for differentiation of the mouse male germline. Biol
Reprod. 2008;79: 696
–703.
Marcon E, Babak T, Chua G, Hughes T, Moens PB. miRNA and piRNA localization in the male mammalian meiotic nucleus. Chromosome Res. 2008;16: 243 –260.[CrossRef][Medline]
Marcon L, Boissonneault G. Transient DNA strand breaks during mouse
and human spermiogenesis new insights in stage specificity and link to
chromatin remodeling. Biol Reprod. 2004; 70: 910
–918.
Mathonnet G, Fabian MR, Svitkin YV, Parsyan A, Huck L, Murata T,
Biffo S, Merrick WC, Darzynkiewicz E, Pillai RS, Filipowicz W, Duchaine TF,
Sonenberg N. MicroRNA inhibition of translation initiation in vitro by
targeting the cap-binding complex eIF4F. Science. 2007; 317: 1764
–1767.
Meister G, Landthaler M, Patkaniowska A, Dorsett Y, Teng G, Tuschl T. Human Argonaute2 mediates RNA cleavage targeted by miRNAs and siRNAs. Mol Cell. 2004;15: 185 –197.[CrossRef][Medline]
Meistrich ML, Brock WA, Grimes SR, Platz RD, Hnilica LS. Nuclear protein transitions during spermatogenesis. Fed Proc. 1978; 37: 2522 –2525.[Medline]
Molnar A, Schwach F, Studholme DJ, Thuenemann EC, Baulcombe DC. miRNAs control gene expression in the single-cell alga Chlamydomonas reinhardtii. Nature. 2007; 447: 1126 –1129.[CrossRef][Medline]
Morales CR, Wu XQ, Hecht NB. The DNA/RNA-binding protein, TB-RBP, moves from the nucleus to the cytoplasm and through intercellular bridges in male germ cells. Dev Biol. 1998; 201: 113 –123.[CrossRef][Medline]
Morlando M, Ballarino M, Gromak N, Pagano F, Bozzoni I, Proudfoot NJ. Primary microRNA transcripts are processed co-transcriptionally. Nat Struct Mol Biol. 2008; 15: 902 –909.[CrossRef][Medline]
Murchison EP, Stein P, Xuan Z, Pan H, Zhang MQ, Schultz RM, Hannon
GJ. Critical roles for Dicer in the female germline. Genes
Dev. 2007;21: 682
–693.
Nagaraja AK, Andreu-Vieyra C, Franco HL, Ma L, Chen R, Han DY, Zhu
H, Agno JE, Gunaratne PH, DeMayo FJ, Matzuk MM. Deletion of Dicer in somatic
cells of the female reproductive tract causes sterility. Mol
Endocrinol. 2008;22: 2336
–2352.
Nottrott S, Simard MJ, Richter JD. Human let-7a miRNA blocks protein production on actively translating polyribosomes. Nat Struct Mol Biol. 2006;13: 1108 –1114.[CrossRef][Medline]
Novotny GW, Sonne SB, Nielsen JE, Jonstrup SP, Hansen MA, Skakkebaek NE, Rajpert-De Meyts E, Kjems J, Leffers H. Translational repression of E2F1 mRNA in carcinoma in situ and normal testis correlates with expression of the miR-17-92 cluster. Cell Death Differ. 2007;14: 879 –882.[CrossRef][Medline]
Okamura K, Hagen JW, Duan H, Tyler DM, Lai EC. The mirtron pathway generates microRNA-class regulatory RNAs in Drosophila. Cell. 2007;130: 89 –100.[CrossRef][Medline]
Oliva R, Mezquita C. Marked differences in the ability of distinct protamines to disassemble nucleosomal core particles in vitro. Biochemistry. 1986; 25: 6508 –6511.[CrossRef][Medline]
Olsen PH, Ambros V. The lin-4 regulatory RNA controls developmental timing in Caenorhabditis elegans by blocking LIN-14 protein synthesis after the initiation of translation. Dev Biol. 1999; 216: 671 –680.[CrossRef][Medline]
O'Rourke JR, Georges SA, Seay HR, Tapscott SJ, McManus MT, Goldhamer DJ, Swanson MS, Harfe BD. Essential role for Dicer during skeletal muscle development. Dev Biol. 2007; 311: 359 –368.[CrossRef][Medline]
Papaioannou MD, Pitetti JL, Ro S, Park C, Aubry F, Schaad O, Vejnar CE, Kuhne F, Descombes P, Zdobnov EM, McManus MT, Guillou F, Harfe BD, Yan W, Jegou B, Nef S. Sertoli cell Dicer is essential for spermatogenesis in mice. Dev Biol. 2009; 326: 250 –259.[CrossRef][Medline]
Petersen CP, Bordeleau ME, Pelletier J, Sharp PA. Short RNAs repress translation after initiation in mammalian cells. Mol Cell. 2006;21: 533 –542.[CrossRef][Medline]
Pfeffer S, Zavolan M, Grasser FA, Chien M, Russo JJ, Ju J, John B,
Enright AJ, Marks D, Sander C, Tuschl T. Identification of virus-encoded
microRNAs. Science. 2004; 304: 734
–736.
Pillai RS, Artus CG, Filipowicz W. Tethering of human Ago proteins
to mRNA mimics the miRNA-mediated repression of protein synthesis.
RNA. 2004;10: 1518
–1525.
Pillai RS, Bhattacharyya SN, Artus CG, Zoller T, Cougot N, Basyuk
E, Bertrand E, Filipowicz W. Inhibition of translational initiation by Let-7
MicroRNA in human cells. Science. 2005; 309: 1573
–1576.
Pradeepa MM, Rao MR. Chromatin remodeling during mammalian spermatogenesis: role of testis specific histone variants and transition proteins. Soc Reprod Fertil Suppl. 2007; 63: 1 –10.[Medline]
Ro S, Park C, Sanders KM, McCarrey JR, Yan W. Cloning and expression profiling of testis-expressed microRNAs. Dev Biol. 2007;311: 592 –602.[CrossRef][Medline]
Schmidt EE, Hanson ES, Capecchi MR. Sequence-independent assembly
of spermatid mRNAs into messenger ribonucleoprotein particles. Mol
Cell Biol. 1999;19: 3904
–3915.
Schwarz DS, Hutvagner G, Du T, Xu Z, Aronin N, Zamore PD. Asymmetry in the assembly of the RNAi enzyme complex. Cell. 2003; 115: 199 –208.[CrossRef][Medline]
Song R, Ro S, Michaels JD, Park C, McCarrey JR, Yan W. Many X-linked microRNAs escape meiotic sex chromosome inactivation. Nat Genet. 2009;41: 488 –493.[CrossRef][Medline]
Steger K. Haploid spermatids exhibit translationally repressed mRNAs. Anat Embryol (Berl). 2001; 203: 323 –334.[CrossRef][Medline]
Su H, Trombly MI, Chen J, Wang X. Essential and overlapping
functions for mammalian Argonautes in microRNA silencing. Genes
Dev. 2009;23: 304
–317.
Suarez Y, Fernandez-Hernando C, Yu J, Gerber SA, Harrison KD, Pober
JS, Iruela-Arispe ML, Merkenschlager M, Sessa WC. Dicer-dependent endothelial
microRNAs are necessary for postnatal angiogenesis. Proc Natl Acad
Sci U S A. 2008;105: 14082
–14087.
Tang F, Kaneda M, O'Carroll D, Hajkova P, Barton SC, Sun YA, Lee C,
Tarakhovsky A, Lao K, Surani MA. Maternal microRNAs are essential for mouse
zygotic development. Genes Dev. 2007; 21: 644
–648.
Vagin VV, Sigova A, Li C, Seitz H, Gvozdev V, Zamore PD. A distinct
small RNA pathway silences selfish genetic elements in the germline.
Science. 2006;313: 320
–324.
Vasudevan S, Tong Y, Steitz JA. Switching from repression to
activation: microRNAs can up-regulate translation.
Science. 2007;318: 1931
–1934.
Wakiyama M, Takimoto K, Ohara O, Yokoyama S. Let-7
micro-RNA-mediated mRNA deadenylation and translational repression in a
mammalian cell-free system. Genes Dev. 2007; 21: 1857
–1862.
Wang B, Love TM, Call ME, Doench JG, Novina CD. Recapitulation of short RNA-directed translational gene silencing in vitro. Mol Cell. 2006;22: 553 –560.[CrossRef][Medline]
Watanabe T, Takeda A, Tsukiyama T, Mise K, Okuno T, Sasaki H,
Minami N, Imai H. Identification and characterization of two novel classes of
small RNAs in the mouse germline: retrotransposon-derived siRNAs in oocytes
and germline small RNAs in testes. Genes Dev. 2006; 20: 1732
–1743.
Wightman B, Ha I, Ruvkun G. Posttranscriptional regulation of the heterochronic gene lin-14 by lin-4 mediates temporal pattern formation in C. elegans. Cell. 1993; 75: 855 –862.[CrossRef][Medline]
Wu XQ, Xu L, Hecht NB. Dimerization of the testis brain RNA-binding
protein (translin) is mediated through its C-terminus and is required for DNA-
and RNA-binding. Nucleic Acids Res. 1998; 26: 1675
–1680.
Yan N, Lu Y, Sun H, Tao D, Zhang S, Liu W, Ma Y. A microarray for
microRNA profiling in mouse testis tissues.
Reproduction. 2007; 134: 73
–79.
Yang J, Chennathukuzhi V, Miki K, O'Brien DA, Hecht NB. Mouse
testis brain RNA-binding protein/translin selectively binds to the messenger
RNA of the fibrous sheath protein glyceraldehyde 3-phosphate dehydrogenase-S
and suppresses its translation in vitro. Biol Reprod. 2003; 68: 853
–859.
Yi R, O'Carroll D, Pasolli HA, Zhang Z, Dietrich FS, Tarakhovsky A, Fuchs E. Morphogenesis in skin is governed by discrete sets of differentially expressed microRNAs. Nat Genet. 2006; 38: 356 –362.[CrossRef][Medline]
Yi R, Qin Y, Macara IG, Cullen BR. Exportin-5 mediates the nuclear
export of pre-microRNAs and short hairpin RNAs. Genes
Dev. 2003;17: 3011
–3016.
Yu Z, Raabe T, Hecht NB. MicroRNA Mirn122a reduces expression of
the posttranscriptionally regulated germ cell transition protein 2 (Tnp2)
messenger RNA (mRNA) by mRNA cleavage. Biol Reprod. 2005; 73: 427
–433.
Zhao T, Li G, Mi S, Li S, Hannon GJ, Wang XJ, Qi Y. A complex
system of small RNAs in the unicellular green alga Chlamydomonas
reinhardtii. Genes Dev. 2007; 21: 1190
–1203.
This article has been cited by other articles:
|
|
 |
|
  S. C. McIver, S. D. Roman, B. Nixon, and E. A. McLaughlin miRNA and mammalian male germ cells Hum. Reprod. Update, January 1, 2012; 18(1): 44 - 59. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. Niu, S. M. Goodyear, S. Rao, X. Wu, J. W. Tobias, M. R. Avarbock, and R. L. Brinster MicroRNA-21 regulates the self-renewal of mouse spermatogonial stem cells PNAS, August 2, 2011; 108(31): 12740 - 12745. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. D. Papaioannou, M. Lagarrigue, C. E. Vejnar, A. D. Rolland, F. Kuhne, F. Aubry, O. Schaad, A. Fort, P. Descombes, M. Neerman-Arbez, et al. Loss of Dicer in Sertoli Cells Has a Major Impact on the Testicular Proteome of Mice Mol. Cell. Proteomics, April 1, 2011; 10(4): M900587-MCP200 - M900587-MCP200. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. D. Johnson, C. Lalancette, A. K. Linnemann, F. Leduc, G. Boissonneault, and S. A. Krawetz The sperm nucleus: chromatin, RNA, and the nuclear matrix Reproduction, January 1, 2011; 141(1): 21 - 36. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Bagarova, T. A. Chowdhury, M. Kimura, and K. C. Kleene Identification of elements in the Smcp 5' and 3' UTR that repress translation and promote the formation of heavy inactive mRNPs in spermatids by analysis of mutations in transgenic mice Reproduction, December 1, 2010; 140(6): 853 - 864. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. K. Bjork, A. Sandqvist, A. N. Elsing, N. Kotaja, and L. Sistonen miR-18, a member of Oncomir-1, targets heat shock transcription factor 2 in spermatogenesis Development, October 1, 2010; 137(19): 3177 - 3184. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
