The manchette is a transient microtubule structure in elongating spermatids that function in shaping the sperm head and delivering proteins for tail elongation. The precise details of how these critical roles remain largely unknown.
Materials and Methods
A random N-ethyl-N-nitrosourea (ENU) mouse mutagenesis screen identified and isolated several novel mouse strains with abnormal spermatogenesis. Mapping and sequencing identified mutations on specific protein coding genes. Yeast two Hybrid assay revealed the new possible binding partners, which were confirmed by immunoprecipitation and immunochemistry.
Results and discussion
One of the mouse models with abnormal phenotype in spermatogenesis was named Kaos mice, which carry the mutation of R528stop in a previously uncharacterized gene, Lrguk1 (leucine-rich repeats and guanylate kinase domain contain). They showed intriguing abnormalities in acrosome attachment, sperm head shaping and the initiation of the axoneme growth, indicating LRGUK1 is critical for manchette functions, such as nuclear shaping and intra-manchette transportation (IMT) i.e. the transport of proteins and vesicles along the microtubules of the manchette. We found that LRGUK1 can binds to all Hook family proteins, RIMBP3, and Kinesin light chain3 (Klc3), all of which are associated with intracellular protein transport as cargo adaptor proteins or motor protein, and are localized to the manchette. They form a multiprotein complex in the manchette of spermatids. LRUGK1 consists of 3 domains, one of which guanylate kinase domain at C terminal is critical for binding to HOOK2 and RIMBP3. These findings suggest the requirement of LRGUK1 for manchette function, especially in intracellular protein transportation and the initiation of sperm tail grown. These data raise the possibility that LRGUK1 dysfunction contributes to the most common male infertility phenotype, oligoasthenoteratozoospermia.