Sperm motility and hence male fertility strictly depends on proper development of the sperm tail and its tight anchorage to the head. The main protein of sperm tail outer dense fibers, ODF1/HSPB10, belongs to the family of small heat shock proteins that function as molecular chaperones. However, the impact of ODF1 on sperm tail formation and motility and on male fecundity is unknown. We therefore generated mutant mice in which the Odf1 gene was disrupted. Heterozygous mutant male mice are fertile while sperm motility is reduced, but Odf1-deficient male mice are infertile due to the detachment of the sperm head. Although headless tails are somehow motile, transmission electron microscopy revealed disturbed organization of the mitochondrial sheath, as well as of the outer dense fibers. Our results thus suggest that ODF1, besides being involved in the correct arrangement of mitochondrial sheath and outer dense fibers, is essential for rigid junction of sperm head and tail. Loss of function of ODF1, therefore, might account for some of the cases of human infertility with decapitated sperm heads. In addition, since sperm motility is already affected in heterozygous mice, impairment of ODF1 might even account for some cases of reduced fertility in male patients.

A main structure of the mammalian sperm tail is a structure known as the outer dense fibers whose molecular composition as well as their function are still mostly unknown. We report here the isolation and characterization of new cDNAs (odf2) that identifies a highly variable gene locus encoding outer dense fiber proteins. Transcription of odf2 is restricted to testis and more specifically to round spermatids. Transcription starts in step 6 spermatids, which coincides with transcription of the major outer dense fiber protein gene odf1 (Burmester, S., and Hoyer-Fender, S. (1996) Mol. Reprod. Dev. 45, 10-20) and with the formation of the sperm tail. Affinity-purified anti-Odf2 antibodies identified isolated outer dense fibers immunocytochemically and detected at least three protein bands in the molecular mass range of 65,000 to 70,000 Da in total Odf protein preparations. Presence of several protein bands correlates with the presence of several transcripts and the isolation of slightly different cDNA clones, whereas Southern blot hybridization does not indicate the presence of multiple genes. Computer analyses of the structure of the encoded Odf2 protein revealed an overall alpha-helical structure with two regions identical to the dimerization region of the leucine zipper motif.

The outer dense fibres (ODF) are a main cytoskeletal structure of the sperm tail. Despite their importance in the morphology and function of the sperm tail, their constituents are poorly described. Here we investigate the protein composition of human outer dense fibres. Our results suggest that human ODF consist of about 10 major and of at least 15 minor proteins, where all major proteins are ODF1, ODF2 or ODF2-related proteins. From a human testis cDNA library, we isolated two slightly different cDNAs encoding ODF2 proteins of approximately 70 kDa. Human ODF2 cDNAs and their encoded proteins are very similar to those isolated from rat and mouse pointing to a high evolutionary pressure residing on these proteins. Transcription of ODF2 is restricted to testis tissue and more specifically to round spermatids as was demonstrated by a non-radioactive in-situ hybridization. ODF2 proteins were detected in the sperm tail. Their distribution along the length of the sperm tail shows that the ODF normally extend to about half the principal piece of the sperm tail. The former result opens the possibility for a screening regarding the distribution of sperm tail proteins related to motility disorders.

No abstract

CHARGE syndrome is an autosomal dominant disorder caused in about two-third of cases by mutations in the CHD7 gene. For other genetic diseases e.g. hereditary spastic paraplegia, it was shown that interacting partners are involved in the underlying cause of the disease. These data encouraged us to search for CHD7 binding partners by a yeast two-hybrid library screen and CHD8 was identified as an interacting partner. The result was confirmed by a direct yeast two-hybrid analysis, co-immunoprecipitation studies and by a bimolecular fluorescence complementation assay. To investigate the function of CHD7 missense mutations in the CHD7-CHD8 interacting area on the binding capacity of both proteins, we included three known missense mutations (p.His2096Arg, p.Val2102Ile and p.Gly2108Arg) and one newly identified missense mutation (p.Trp2091Arg) in the CHD7 gene and performed both direct yeast two-hybrid and co-immunoprecipitation studies. In the direct yeast two-hybrid system, the CHD7-CHD8 interaction was disrupted by the missense mutations p.Trp2091Arg, p.His2096Arg and p.Gly2108Arg, whereas in the co-immunoprecipitation studies disruption of the CHD7-CHD8 interaction by the mutations could not be observed. The results lead to the hypothesis that CHD7 and CHD8 proteins are interacting directly and indirectly via additional linker proteins. Disruption of the direct CHD7-CHD8 interaction might change the conformation of a putative large CHD7-CHD8 complex and could be a disease mechanism in CHARGE syndrome.