According to a worldwide survey in 2010 infertility affects 48.5 million of couples. In roughly half of the cases infertility is provoked by the male mate. Thus, a significant percentage of young men are infertile but the underlying causes are mostly unknown. Male fertility and reproduction success critically depends on proper formation of the mature sperm. Transmission of the genetic information, harboured in the sperm head, is achieved by tail propelled directed movement. Since impaired sperm motility is a frequent cause of male infertility, the sperm tail cytoskeleton has come into focus in male infertility diagnostics and as a prognostic factor in assisted conception in human. For directed movement of the sperm and fertilization, the sperm tail has to be tightly connected to the sperm head. A sophisticated structure, known as the head-to-tail coupling apparatus, or shortened HTCA, is the morphological equivalent of head to tail anchorage. The mature HTCA is well described at its ultra-structural level but information about its development during sperm formation, the precursors from which it originated, and its molecular composition is scarce. We have previously shown that the major sperm tail protein ODF1 is essential for the tight linkage of sperm head to tail. Absence of ODF1 in mice caused sperm decapitation and male infertility whereas haplo-deficiency of ODF1 provoked weakening of head-to-tail linkage and severe subfertility in male mice. We have also generated mice deficient for an interaction partner of ODF1that suffer from male infertility. We are currently investigating haplo-deficient and knock out mice at the molecular and cytological level. Our intention is to figure out the formation of the HTCA during spermiogenesis at its molecular and ultra-structural level taking advantage of our knock out model systems.
Materials and methods
We first generated and analysed knock out mice and investigated the phenotypic effects at the molecular and cytological level.
We have generated Odf1-deficient mice on C57BL/6J genetic background and found that homozygous males are infertile. However, spermatogenesis proceeded almost normally based on histological inspection and expression analysis of marker genes by RT-PCR Ultra-structural inspection of spermatozoa demonstrated that loss of ODF1 caused disturbance of the mitochondrial sheath, and affected the tight association of the outer dense fibers to their corresponding microtubule doublets. The most striking phenotype, however, was complete detachment of sperm heads resulting in acephalic sperm and male infertility. In contrast, haplo-deficient spermatozoa were ultra-structurally normal. However, we found that haplo-deficiency of ODF1 provoked weakening of head-to-tail linkage and severe subfertility in incipient congenic male mice. Additionally, we identified an interaction partner of ODF1 situated in the nuclear membrane that itself caused weakening of the head-to-tail linkage in the haplo-deficient condition similar to ODF1 haplo-deficiency.
We have identified the first molecular components of the head-to-tail linkage apparatus. Characterization of the molecular components of the HTCA as well as a precise analysis of HTCA formation and its disturbances will eventually be instrumental for infertility diagnostics, assisted reproduction and development of male contraceptives.