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Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island.
| Correspondence to: Dr Kim Boekelheide, Department of Pathology and Laboratory Medicine, 175 Meeting St, Brown University, Providence, RI 02912 (Fax: 401-863-9008; e-mail: Kim_Boekelheide{at}Brown.edu). |
| Received for publication April 8, 2003; accepted for publication June 12, 2003. |
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Abstract |
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Key words: Testis, phosphoinositide-3 kinases, protein kinase B, perinulear, Golgi
Phosphoinositide-3-kinases (PI3Ks) have emerged as key determinants in the regulation of critical cellular responses. Several biological effects of PI3Ks are mediated through the activation of the downstream target, Akt/protein kinase B (PKB). Akt1 is a serine/threonine protein kinase that plays an important role in signaling pathways that regulate cell growth, proliferation, and differentiation (Alessi et al, 1997; Franke et al, 1997; Brazil et al, 2002). Three major isoforms of Akt/PKB exist: Akt1/PKB alpha Akt2/PKB beta, and Akt3/PKB gamma, which are encoded by three separate genes with more than 85% sequence identity in mammalian cells (Alessi and Cohen, 1998; Coffer et al, 1998; Downward, 1998; Kandel and Hay, 1999). In response to a variety of stimuli (eg, growth factors, hormones, and cytokines), Akt1 is recruited from the cytosol to the plasma membrane by the products of PI3Ks, phosphatidylinositol (3,4)-diphosphate [PtdIns(3,4)P2], and phosphatidylinositol (3,4,5)-triphosphate [PtdIns(3,4,5)P3] (Delcommenne et al, 1998; Simpson and Parsons 2001; Neri et al, 2002). Akt1 is then fully activated on phosphorylation at threonine-308 and serine-473. Numerous Akt1 substrates have been identified and include BAD, members of the forkhead family of transcription factors, CREB, Ik-B kinase, procaspase 9, GSK3, mTOR, p21, and p27 (Delcommenne et al, 1998; Neri et al, 2002).
One important prosurvival pathway associated with spermatogenic growth and development is the SCF/c-Kit/PI3K/Akt1 signal transduction pathway. The Kit/SCF-receptor is required for normal hematopoiesis, melanogenesis, and gametogenesis (Blume-Jensen et al, 2000). Disruption of the PI3K binding site in the Kit/SCF receptor provided the first in vivo model for male sterility caused by a discrete signaling pathway defect affecting early germ cells (Blume-Jensen et al, 2000). Subsequent downstream signaling initiated by c-kit involves multiple pathways, including phosphatidylinositol-3-kinase, Src family members, the JAK/STAT pathway, and the Ras-Raf-MAP kinase cascade (Linnekin, 1999). To date, detailed investigations of these signal transduction pathways have been largely limited to the hematopoietic system, with little information available about other biological systems. Besides the role that Akt1 plays in germ cell survival and proliferation (Feng et al, 2000; Chen et al, 2001), Akt1 is implicated as a downstream target in a PI3K-dependent signal transduction pathway in neonatal rat Sertoli cells (Meroni et al, 2002). Likewise, others have shown that hormonal or insulin-like growth factor 1-mediated stimulation of neonatal rat Sertoli cells activates Akt1 via a PI3K-dependent pathway (Khan et al, 2002).
Of interest, homozygous deletion of the most ubiquitously expressed isoform, Akt1, leads to spontaneous apoptosis and attenuation of spermatogenesis in the mouse testis (Chen et al, 2001). Increased spontaneous apoptosis is also observed in the thymus. Akt1-/- mice are smaller than wild-type littermates and have a shortened lifespan on exposure to genotoxic stress, and mouse embryonic fibroblasts from these mice are significantly more susceptible to apoptosis on exposure to ultraviolet irradiation, tumor necrosis factor alpha, Fas-stimulating antibody, and serum withdrawal (Chen et al, 2001). Therefore, we hypothesized that the Akt1 gene plays a critical role as a growth and/or survival factor during testicular growth and development. To provide the basis for exploring this hypothesis, we examined expression and localization of total Akt1 and phosphorylated Akt1 in the developing and adult wild-type rat testis. Our results demonstrate for the first time the expression of total Akt1 and phosphorylated Akt1 in the rat testis in vivo. In addition, total Akt1 localizes to the perinuclear region of germ cells and the supranuclear region of Sertoli cells. This perinuclear staining was found to be associated with the Golgi complex in both germ and Sertoli cells.
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Methods |
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Antibodies
Primary antibodies and working dilutions included phosphorylated Akt1
(Thr308) diluted 1 : 500 (Cell Signaling, Beverly, Mass); total Akt1 diluted 1
: 1000 (Santa Cruz Biotechnology, Inc, Santa Cruz, Calif); Flotillin-2 diluted
1 : 250 (BD Transduction Laboratories, San Diego, Calif); centrin 20H5
(described in Sanders and Salisbury,
1994) diluted 1:100, Golgi 58K-9 mouse monoclonal antibody diluted
1 : 50 (Sigma-Aldrich, St Louis, Mo); alpha mannosidase II rabbit polyclonal
antibody diluted 1 : 100 (gift from K. Moremen), and beta actin diluted 1 :
2000 (Sigma-Aldrich). Secondary antibodies and working dilutions included
horseradish peroxidase-conjugated anti-rabbit IgG (from donkey) (Amersham
Pharmacia Biotech, Piscataway, NJ) diluted 1 : 1000, horseradish
peroxidase-conjugated anti-mouse IgG (from sheep) (Amersham Pharmacia Biotech)
diluted 1 : 1000, rabbit anti-mouse Alexa Fluorochrome 593 (Molecular Probes,
Eugene, Ore) diluted 1 : 400, and rabbit anti goat Alexa Fluorochrome 488
(Molecular probes) diluted 1 : 400.
Western Blotting
Whole testis from postnatal days 7, 21, 28, and 40 and adult rats were
weighed, detunicated, and homogenized, in three volumes of ice-cold RIPA
buffer (50 mM Tris [pH 7.4], 150 mM NaCl, 1% NP-40, 0.5% deoxycholate, and
0.1% sodium dodecyl sulfate [SDS]) that contained a protease inhibitor mixture
(P2714; Sigma), by 10 strokes in a Dounce homogenizer. The numbers of animals
used at each time point (postnatal day 7 through adult) were 7, 4, 3, 3, and
2, respectively. Protein concentrations were determined by Bradford protein
assay (Bio-Rad, Hercules, Calif). Protein samples were then subjected to
SDS-polyacrylamide gel electrophoresis (PAGE) analysis in 10% gels and
transferred to polyvinylidene difluoride membranes (Millipore Corp, Bedford,
Mass). Protein levels in each homogenate were similar according to the results
of Coomasie blue staining of polyacrylamide gels. The membranes were blocked
for 1 hour at room temperature in 50 mM Tris (pH 7.5) that contained 0.1%
Tween 20. Blots were incubated overnight at 4°C in primary antibody
(phosphorylated Akt 1 : 500; Cell Signaling) and total Akt1 (1 : 1000; Santa
Cruz Biotechnology). For detection, membranes were incubated for 1 hour at a 1
: 1000 dilution of horseradish peroxidase-linked IgG (Santa Cruz
Biotechnology). Membranes were exposed to Biomax light ECL film (Amersham
Pharmacia Biotech).
Immunostaining
For cryosections, unfixed testes were submerged in OCT embedding medium
(Sekura Finetek, Inc, Torrance, Calif) and snap frozen by immersion in liquid
nitrogen. Sections were then cut to 6 µm thickness and mounted on
poly-L-lysine-coated glass slides (VWR Scientific, West Chester, Penn). To
better ascertain the cell types responsible, testis touch preparations were
also conducted according to a method described elsewhere (Johnson and
Boekelheide, 2000). In brief, adult testes were cut in cross-section with a
razor blade, and then exposed seminiferous tubules were briefly touched to a
glass slide (VWR Scientific). After air drying, slides were treated exactly as
they were for cryosection immunostaining. For phosphorylated Akt1 staining,
slides were fixed for 3 minutes in -20°C methanol. For the localization of
both Akt1 and flotillin-2 and Akt1 and centrin, slides were fixed for 1 minute
in -20°C acetone. For the localization of Akt1 with Golgi 58K-9 antibody,
slides were fixed in 2% paraformaldehyde/0.05% Triton X100/0.02%SDS in
phosphate-buffered saline (PBS) for 20 minutes, and, for localization of Akt1
with alpha mannosidase II, a Sertoli cell-specific Golgi primary antibody,
slides were fixed in 4% paraformaldehyde/PBS for 3 minutes.
Slides were blocked in 3% normal bovine serum albumin/0.1% Triton/PBS for 1 hour and then washed in 0.1% Triton/PBS (3x) for 5 minutes each. All incubations with primary antibodies were done overnight. Negative controls were incubated overnight in either normal goat serum (total Akt1), normal rabbit serum (phosphorylated Akt1), or normal mouse IgG at the concentration of the primary antibody. For the color figures, images were obtained using a Spot RT camera (Diagnostic Instruments, Inc, Sterling Heights, Mich) mounted to a Nikon Eclipse E800 microscope (MVI, Avon, Maaa) and were downloaded into Photoshop 6.0 software (Adobe Systems, Inc, San Jose, Calif).
Lipid Raft Isolation
With minor modifications, 1% Triton was used in the lysis buffer rather
than 0.05%, according to protocols established elsewhere (Field et al,
1995,
1997), and the lipid raft
fraction was isolated from adult rat testis homogenate. In brief, rat testis
(0.4 g) was homogenized in ice-cold lysis buffer that contained 1% Triton,
using a Dounce homogenizer. To remove nuclei and unlysed cells, homogenates
were centrifuged at 1800 rpm, and the supernatant was collected. One
milliliter of supernatant was diluted with an equal volume of 80% sucrose in
Tris-buffered saline and overlaid with 30% sucrose and 5% sucrose in TBS. The
column was centrifuged for 16 hours at 140 000 g in an SW40Ti rotor. Fractions
(1 mL) were then collected from the top. For fractions 1-10, 3 volumes of TBS
were added, and then this was centrifuged at 150 000 g in a Type 50 rotor for
1.5 hours at 4°C, to concentrate the fractions. After concentration, the
pelleted material was resuspended in 120 µL of TBS. All fractions were
diluted with 6x sample buffer, and 10 µL was loaded per lane for
electrophoresis (12% SDS-PAGE).
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Results |
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Total Akt1 Expression in Postnatal Spermatogenic Development
To confirm that Akt1 protein is expressed during spermatogenesis and to
investigate the cell types responsible for Akt1 expression, we immunostained
rat testis cryosections during a postnatal development sequence with primary
antibody to Akt1. Akt1 immunostaining (green) demonstrated a mainly
cytoplasmic localization in the testis
(Figure 2A through D) with an
additional, prominent staining of a perinuclear structure
(Figure 2B through D). This
perinuclear immunostaining was apparent from postnatal days 21 into adulthood
as large, green ovoid bodies near to the periphery of the nucleus in
spermatocytes (Figure 2B through
D; arrowheads). In the adult testis
(Figure 2D), Akt1
immunostaining was observed to localize within spermatocytes (arrowheads) and
as bright single green dots visible in elongating spermatids
(Figure 2D; asterisks).
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Phosphorylated Akt1 Expression in Testis Postnatal Development
To investigate the cell types responsible for phosphorylated Akt1
expression, we again used immunohistochemical analysis. On the basis of
locations within the seminiferous tubule, cell size, and morphology,
Figure 2E through H illustrates
the mainly nuclear germ cell localization of phosphorylated Akt1 (Thr 308) in
the testis throughout postnatal development. At postnatal day 7,
phosphorylated Akt1 immunostaining was most pronounced in the germ cells of
the testis and exhibited a bright punctate staining pattern
(Figure 2E; arrowheads). At
postnatal days 21 and 28 (Figure 2F and
G; arrowheads), phosphorylated Akt1 immunostaining was prominent
in the nuclei of pachytene spermatocytes and exhibited a bright punctate
staining pattern. In the adult testis, phosphorylated Akt1 immunostaining was
observed in the nuclei of spermatocytes and round spermatids
(Figure 2H; arrowheads).
Similar to total Akt1, the phosphorylated Akt1 pattern was apparent in
elongating spermatids, as single bright red spots
(Figure 2H; arrowheads). Taken
together, this suggests that phosphorylated Akt1 expression is associated most
prominently with spermatocytes and round spermatids during spermatogenic
development.
Akt1 Is Present in the Golgi Complex of Both Germ and Sertoli
Cells
On the basis of the perinuclear localization of Akt1 in germ cells,
immunofluorescence experiments were conducted to determine whether the
observed Akt1-associated perinuclear staining associated with either the Golgi
apparatus and/or the centrosome. Both of these structures are associated with
the perinuclear region during spermatogenesis
(McGuinness and Orth, 1992;
Manandhar and Schatten, 2000). Cross sections of rat testis were fixed and stained with primary antibodies to
both total Akt1 and also with two different primary antibodies which recognize
the Golgi complex, 58K-9, (Ktistakis et
al, 1991) or alpha mannosidase II, which specifically stains for
the Golgi complex in Sertoli cells
(Igdoura et al, 1999).
Immunostaining with the 58K-9 antibody demonstrated localization of Akt1
within the Golgi apparatus of spermatocytes
(Figure 3A through D). On the
basis of location, size, and cell morphology, Golgi-associated perinuclear
staining was found to be prominent in spermatocytes and began to diminish in
round spermatids. It was absent in elongating and mature spermatids.
Immunostaining with alpha mannosidase II demonstrated that Akt1 prominently
associated with the Golgi complex of Sertoli cells
(Figure 3C and D).
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Flotillin-2 and Centrin Are Present in a Perinuclear Structure in
Spermatocytes and Round Spermatids
Double immunofluorescence experiments were also conducted with flotillin-2
and centrin both of which have been reported to localize to the centrosome in
various cell types (Manadhar et al, 1999;
Solomon et al, 2002). On the
basis of cell size and morphology, testis touch preparations demonstrated that
flotillin-2 (red) was also expressed in proximity with Akt1 (green;
arrowheads) at a perinuclear structure in pachytene spermatocytes
(Figure 3E). In addition to
flotillin-2 staining centrosomes, staining was also noted around the basement
membrane of the testis (data not shown).
Figure 3F demonstrates that
centrin was expressed in proximity with Akt1 (green; arrowheads) at the
perinuclear structure in primary spermatocytes. On the basis of the presence
of Akt1, flotillin-2, and centrin within the perinuclear structure, we
investigated whether Akt1 physically associated with either flotillin-2 or
centrin in adult whole testis homogenates. Immunoprecipitation-Western
analysis revealed no physical association of Akt1 with either flotillin-2 or
centrin (not shown).
Flotillin-2, but Not Akt1, Is Associated with the Lipid Raft
Component in the Adult Testis
To determine whether Akt1 and flotillin-2, a known lipid raft-associated
protein (Volonte et al, 1999;
Salzer, et al, 2001;
Solomon et al, 2002), were
contained in lipid raft domains, an adult rodent testis was fractionated
according to previously established protocols on the basis of low-density
detergent solubility and density centrifugation. Although trace amounts of
Akt1 were found in the lipid raft fractions, Akt1 was predominantly localized
to the denser non-lipid raft fractions
(Figure 4, fractions 8 and 9;
asterisks). In contrast, flotillin-2, a known microdomain-associated lipid
raft marker (Volonte et al,
1999; Salzer et al,
2001; Solomon et al,
2002) was predominantly found in known lipid raft fractions 4 and
5 (Figure 4; asterisks).
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Discussion |
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The results of several studies in amphibians and invertebrates have shown that activated Akt1 is sufficient for meiotic resumption in oocytes (Andersen et al, 1998), and, in the starfish Asterina pectinnifera, Akt kinase phosphorylates and down-regulates Myt1, allowing for the initial activation of cyclinB/cdc 2 at the G2/M phase transition during meiosis (Okumura et al, 2002). Taken together, the expression data support an in vivo role for both Akt1 and activated Akt1 either at a mitotic cell cycle event and/or at the prophase 1 stage of meiosis during spermatogenesis.
To determine the nature of the Akt1-associated staining in the perinuclear region of germ cells, an examination of proteins associated with either the Golgi apparatus or centrosome was conducted. Akt1 was found to associate within the Golgi complex in both the perinuclear region of spermatocytes and round spermatids. This signal was absent in elongating and mature spermatids. Of interest, Akt1 also associates with the Golgi complex in the supranuclear region of Sertoli cells.
In addition to the Golgi markers, flotillin-2, a novel marker for lipid rafts (Lang et al, 1998; Salzer et al, 2001) and the centrosome in peripheral blood mononuclear cells (Solomon et al, 2002), and centrin, a centrosomal marker (Manadhar, 1998), were present in the Akt1-associated perinuclear region in spermatocytes. However, the results of immunoprecipitation-Western analysis did not demonstrate a physical association between either Akt1 and flotillin-2 or Akt1 and centrin, which indicates that these proteins do not physically interact. Perhaps more noteworthy is the observation that flotillin-2 is predominately found in the lipid raft fraction of the testis, as has been observed in other cell types (Salzer et al, 2001; Nebl et al, 2002).
In summary, our results confirm that Akt1 and phosphorylated Akt1 are expressed both during spermatogenic development and in the adult rat testis. Also, the localization patterns differ, with total Akt1 exhibiting a mainly cytoplasmic localization, whereas phosphorylated Akt1 exhibits a prominent nuclear localization. Total Akt1 was found to localize to the perinuclear region of germ cells and the supranuclear region of Sertoli cells. This region appears to be associated with the Golgi complex in both germ and Sertoli cells. Taken together, it is interesting to speculate that the Golgi-associated Akt1 staining observed in the perinuclear region of spermatocytes and Sertoli cells may represent a novel trafficking pathway for Akt1 activation in the testis.
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Footnotes |
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References |
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Alessi DR, Deak M, Casamayor A, et al. 3-Phosphoinositide-dependent protein kinase-1 (PDK1): structural and functional homology with the Drosophila DSTPK61 kinase. Curr Biol. 1997; 7:776-789.[Medline]
Andersen CB, Roth R, Conti M. Protein kinase B/Akt induces
resumption of meiosis in Xenopus oocytes. J Biol Chem. 1998; 273:18705-18708.
Blume-Jensen P, Jiang G, Hyman R, Lee KF, O'Gorman S, Hunter T. Kit/stem cell factor receptor-induced activation of phosphatidylinositol 3'-kinase is essential for male fertility. Nat Genet. 2000; 24:157-162.[Medline]
Chen WS, Xu PZ, Gottlob K, et al. Growth retardation and increased
apoptosis in mice with homozygous disruption of the Akt1 gene.
Genes Dev. 2001; 15:2203-2208.
Coffer PJ, Jin J, Woodgett JR. Protein kinase B (c-Akt): a multifunctional mediator of phosphatidylinositol 3-kinase activation. Biochem J. 1998; 335:1-13.
Delcommenne M, Tan C, Gray V, Rue L, Woodgett J, Dedhar S.
Phosphoinositide-3-OH kinase-dependent regulation of glycogen synthase kinase
3 and protein kinase B/AKT by the integrin-linked kinase. Proc Natl
Acad Sci USA. 1998; 95:11211-11216.
Downward J. Mechanisms and consequences of activation of protein kinase B/Akt. Curr Opin Cell Biol. 1998; 2:262-267.
Eddy EM. Regulation of gene expression during spermatogenesis. Semin Cell Dev Biol. 1998; 9:451-457.[Medline]
Feng LX, Ravindranath N, Dym M. Stem cell factor/c-kit up-regulates
cyclin D3 and promotes cell cycle progression via the phosphoinositide
3-kinase/p70 S6 kinase pathway in spermatogonia. J Biol
Chem. 2000; 275:25572-25576.
Field KA, Holowka D, Baird B. Fc epsilon RI-mediated recruitment of
p53/56lyn to detergent-resistant membrane domains accompanies cellular
signaling. Proc Natl Acad Sci USA. 1995; 92:9201-9205.
Field KA, Holowka D, Baird B. Compartmentalized activation of the
high affinity immunoglobulin E receptor within membrane domains. J
Biol Chem. 1997; 272:4276-4280.
Griswold MD. The central role of Sertoli cells in spermatogenesis. Semin Cell Dev Biol. 1998; 9:411-416.[Medline]
Igdoura SA, Herscovics A, Lal A, Moremen KW, Morales CR, Hermo L. Alpha-mannosidases involved in N-glycan processing show cell specificity and distinct subcompartmentalization within the Golgi apparatus of cells in the testis and epididymis. Eur J Cell Biol. 1999; 78:441-452.[Medline]
Johnson KJ, Boekelheide K. Dynamic testicular adhesion junctions
are immunologically unique. I: localization of p120 catenin in rat testis.
Biol Reprod. 2002; 66:983-991.
Kandel ES, Hay N. The regulation and activities of the multifunctional serine/threonine kinase Akt/PKB. Exp Cell Res. 1999; 253:210-229.[Medline]
Khan SA, Ndjountche L, Pratchard L, Spicer LJ, Davis JS.
Follicle-stimulating hormone amplifies insulin-like growth factor I-mediated
activation of AKT/protein kinase B signaling in immature rat Sertoli cells.
Endocrinology. 2002; 143:2259-2267.
Ktistakis NT, Roth MG, Bloom GS. PtK1 cells contain a
nondiffusible, dominant factor that makes the Golgi apparatus resistant to
brefeldin A. J Cell Biol. 1991; 113:1009-1023.
Lang DM, Lommel S, Jung M, et al. Identification of reggie-1 and reggie-2 as plasma membrane-associated proteins which cocluster with activated GPI-anchored cell adhesion molecules in non-caveolar micropatches in neurons. J Neurobiol. 1998; 37:502-523.[Medline]
Linnekin, D. Early signaling pathways activated by c-Kit in hematopoietic cells. Int J Biochem Cell Biol. 1999; 31:1053-1074.[Medline]
Manandhar G, Schatten G. Centrosome reduction during rhesus spermiogenesis: gamma-tubulin, centrin, and centriole degeneration. Mol Reprod Dev. 2000; 56:502-511.[Medline]
Manandhar G, Simerly C, Salisbury JL, Schatten G. Centriole and centrin degeneration during mouse spermiogenesis. Cell Motil Cytoskeleton. 1999; 43:137-144.[Medline]
McGuinness MP, Orth JM. Gonocytes of male rats resume migratory activity postnatally. Eur J Cell Biol. 1992; 59:196-210.[Medline]
Meroni SB, Riera MF, Pellizzari EH, Cigorraga SB. Regulation of rat Sertoli cell function by FSH: possible role of phosphatidylinositol 3-kinase/protein kinase B pathway. J Endocrinol. 2002; 174:195-204.[Abstract]
Nebl T, Pestonjamasp KN, Leszyk JD, Crowley JL, Oh SW, Luna EJ.
Proteomic analysis of a detergent-resistant membrane skeleton from neutrophil
plasma membranes. J Biol Chem. 2002; 277:43399-43409.
Neri LM, Borgatti P, Capitani S, Martelli AM. The nuclear phosphoinositide 3-kinase/AKT pathway: a new second messenger system. Biochim Biophys Acta. 2002; 1584:73-80.[Medline]
Okumura E, Fukuhara T, Yoshida H, et al. Akt inhibits Myt1 in the signalling pathway that leads to meiotic G2/M-phase transition. Nat Cell Biol. 2002; 4:111-116.[Medline]
Salzer U, Prohaska R. Stomatin, flotillin-1, and flotillin-2 are
major integral proteins of erythrocyte lipid rafts.
Blood. 2001; 97:1141-1143.
Sanders MA Salisbury JL. Centrin plays an essential role in
microtubule severing during flagellar excision in Chlamydomonas
reinhardtii. J Cell Biol. 1994; 124:795-805.
Schlatt S, Meinhardt A, Nieschlag E. Paracrine regulation of cellular interactions in the testis: factors in search of a function. Eur J Endocrinol. 1997; 137:107-117.[Abstract]
Simpson L, Parsons R. PTEN: life as a tumor suppressor. Exp Cell Res. 2001; 264:29-41.[Medline]
Sinha Hikim AP, Swerdloff RS. Hormonal and genetic control of germ cell apoptosis in the testis. Rev Reprod. 1999; 4:38-47.[Abstract]
Solomon S, Masilamani M, Rajendran L, Bastmeyer M, Stuermer CA, Illges H. The lipid raft microdomain-associated protein reggie-1/flotillin-2 is expressed in human B cells and localized at the plasma membrane and centrosome in PBMCs. Immunobiology. 2002; 205:108-119.[Medline]
Volonte D, Galbiati F, Li S, Nishiyama K, Okamoto T, Lisanti MP.
Flotillins/cavatellins are differentially expressed in cells and tissues and
form a hetero-oligomeric complex with caveolins in vivo. Characterization and
epitope-mapping of a novel flotillin-1 monoclonal antibody probe. J
Biol Chem. 1999; 274:12702-12709.
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