The molecular characterisation of Hook1 and its putative interacting proteins in haploid male germ cell differentiation
The murine Hook1 gene has an essential role in the differentiation process of haploid male germ cells. In homozygous azh-mice (abnormal spermatozoon head shape) Hook1 function is disrupted due to the deletion of exons 10 and 11 leading to a truncated Hook1 polypeptide. Wild type Hook1 protein consists of three putative domains: an N-terminal microtubule binding domain, a central homodimerization domain and a C-terminal organelle binding domain. In azh-males the mutated Hook1 bears only the N-terminal domain while the two other domains are deleted. The loss of Hook1 functions results in an abnormal head shape of all spermatozoa, most probably due to a disturbed structure of the microtubular manchette. Moreover, a fragile connection between the spermatid head and the flagella is often observed leading to a detachment of head and tail. Immunohistochemical localization studies of the Hook1 wild type protein to the manchette and to the spermatid head – tail implantation region suggest different putative functions of Hook1 in male germ cell differentiation. In addition, interaction of Hook1 with other male germ cell proteins can be assumed.
Therefore, we performed a yeast-two-hybrid screen using a murine testicular library and identified different polypeptides as putative Hook1 interacting proteins. In the project supported by the FWF six of these polypeptides and the corresponding genes will be analysed. In a first step the interaction of the six different polypeptides with Hook1 will be proven by immunoprecipitation assays as well as putative co-localization in male germ cells will be analysed. The molecular characterization of Hook1 and its putative interacting proteins will increase our knowledge concerning the processes during spermiogenesis and will add information concerning the role of the manchette in this differentiation process. Due to the high similarity of murine and human Hook1 proteins it can be assumed that both have a comparable function in spermatogenesis. Therefore, it can be expected that the intended project will also add substantial information to the understanding of human haploid male germ cell differentiation and will give clues to the reasons of male infertility.
Dyneins belong to the motor proteins that convert chemical energy from ATP hydrolysis into mechanical work. Axonemal dyneins are involved in the generation of ciliar and flagellar motility and consist of heavy chains, intermediate, light intermediate and light chains.
Impaired ciliary and flagellar functions resulting in male infertility, situs inversus and recurrent respiratory tract infections are found in patients suffering from primary ciliary dyskinesia (PCD, OMIM 242650). We have identified dynein genes and studied their function by generation of mouse models. Analyses of these knock out mice indicate that dynein function is essential form male fertility but is also necessary for early embryonic development.