Involvement of an uncharacterised microtubule-severing enzyme, KATNAL2, in spermatogenesis (#32)
The regulation of microtubule dynamics is essential for many processes required for male fertility, including cell division, determination of cell shape and flagellum formation. Katanin is a microtubule-severing enzyme complex consisting of a p60 microtubule-severing enzyme subunit (Katna1), and a p80 regulatory subunit (Katnb1) thought to modulate p60 enzyme targeting and activity. We recently showed that a mutation in p80 katanin causes sterility in male mice due to abnormalities in microtubule-based structures involved in meiotic division, sperm head shaping and flagellum development1. We showed p80 katanin is important for the regulation of microtubule dynamics in the meiotic spindle, the spermatid manchette and the axoneme, supporting the premise that the p80-p60 complex is required for microtubule-severing in germ cells. Two additional p60 protein homologs are also expressed in the testis. A mutation in one homolog, Katnal1, causes male sterility and disturbed microtubule dynamics in Sertoli cells2. The current study aimed to examine the function and testicular localisation of an uncharacterised p60-like protein (KATNAL2). Sequence analysis indicated KATNAL2 differs from p60 in both sequence and domain organisation. They possess 63% homology in the ATPase enzyme domain but <20% homology in other domains, raising the possibility of distinct mechanisms of action. To determine whether KATNAL2 severs microtubules, HEK293 cells stably expressing tetracycline-inducible constructs of KATNAL2 and p60 were generated. Overexpression of p60 or KATNAL2 resulted in microtubule destruction, providing the first evidence that KATNAL2 can sever microtubules. Katnal2 mRNA was predominantly expressed in testis, and increased during the first appearance of spermatocytes and spermatids, suggesting germ cell expression. Immunohistochemistry revealed KATNAL2 localised to discrete sites within spermatocyte and spermatid cytoplasm and within the sperm flagellum. In conclusion, a third katanin enzyme subunit is present within the testis, has microtubule severing activity and likely modulates microtubule dynamics during male gamete development.
- O’Donnell L, Rhodes D, Smith SJ, Merriner DJ, Clark BJ, Borg C, Whittle B, O’Connor AE, Smith LB, McNally F, de Kretser DM, Goodnow CC, Ormandy CJ, Jamsai D, O’Bryan MK 2012 An essential role for p80 katanin and microtubule severing in male gamete production. PLOS Genetics. 8(5): e1002698.
- Smith LB, Milne L, Nelson N, Eddie S, Brown P, Atanassova N, O’Bryan MK, O’Donnell L, Rhodes D, Wells S, Napper D, Nolan P, Lalanne Z, Cheeseman M, Peters J. 2012 KATNAL1 regulation of Sertoli cell microtubule dynamics is essential for spermiogenesis and male fertility. PLOS Genetics. 8(5): e1002697.