Figure 6. Potential DNA regulatory elements for spermatid-specific expression. (A) Gene promoters that target spermatid-specific expression, including size of the promoter fragment studied and transcription factor motifs present within the promoter fragment. (B) Alignment of 5'-flanking sequences of mouse, rat, and human Cres (cystatin-related epididymal spermatogenic) genes. Sequence similarity between the proximal promoters of mouse and rat, 83%; mouse and human, 50%; and rat and human, 53%. Boxes indicate regions of high identity between the promoters of all 3 species, which could be important for germ cell-specific expression.