MOUSE ODF2 CDNAS CONSIST OF EVOLUTIONARY CONSERVED AS WELL AS HIGHLY VARIABLE SEQUENCES AND ENCODE OUTER DENSE FIBER PROTEINS OF THE SPERM TAIL

The outer dense fibers (ODF) of the mammalian sperm tail comprise a un ique, specialized, and very prominent structure, consisting of nine fi bers surrounding the axoneme. The ODF may play an important but as yet undefined role in sperm morphology, integrity and function. Study of the ODF is hampered by insufficient knowledge of their protein composi tion and the genetic regulation of their synthesis. We report here on the characterization of cDNAs encoding the Odf2 proteins of outer dens e fibers of mouse sperm. We isolated two cDNA clones with variable 5' regions. Variability in sequence is restricted to specific regions in the N-terminal part of the encoded proteins, whereas the C-terminal pa rt is highly conserved in Odf2 proteins both between species and withi n a species. This variability is confirmed at the protein level. The o uter dense fibers could be detected immunologically in total sperm tai ls allowing a direct comparison of their length in relation to the len gth of the sperm tail. Odf2 transcripts could be demonstrated in testi cular RNA and are restricted to germ cells. The start of transcription is in step 5 spermatids of tubular stage V and the RNA could be detec ted in the cytoplasm of differentiating spermatids in all subsequent t ubular stages. (C) 1998 Wiley-Liss, Inc.