Figure 3

Patterns of expression of L1 RNA, ORF1p, and ORF2p duringspermatogenesis. Available data suggest that the synthesis of full-sizeL1 RNP consisting of FL-L1 RNA, ORF1p, and ORF2p is repressed duringspermatogenesis. No L1-related products have been found in spermatogonia.Transient expression of FL-L1 RNA and ORF1p (but not ORF2p) occurs inspermatocyte I at the onset of meiosis (leptotene through mid-pachytene stageof prophase I). These upregulated FL-L1s are implicated in chromosome pairing [145]. Transcription of L1s resumes in spermatocyte II and continues inspermatids. However, L1 RNAs are mostly short, spliced, and prematurelypolyadenylated species that translate into either ORF1p or ORF2p. Theirfunctional significance is not known. Transcription of L1s, ORF1p, and ORF2p isdownregulated by the spermatozoa stage. A small amount of FL-L1 RNA (notdetectable by Northern blotting) is available in spermatozoa. ORF2p, not foundin testicular spermatozoa [18], is detectable in the sub-acrosomal space in mature sperm [27].