Oral Virtual Presentation (Virtual only) ESA-SRB-ANZBMS 2021

Katanin microtubule-severing enzymes are key microtubule regulators. Previously, we showed a hypomorphic mutation in the katanin regulatory B-subunit Katnb1 disrupts germ cell microtubule dynamics resulting in production of abnormal sperm. Herein, we sought to define the full range of KATNB1 spermatogenesis functions using a graded series of KATNB1 loss-of-function (LOF) mouse models. This consisted of Katnb1 hypomorphic (Katnb1^Taily/Taily), compound heterozygous Katnb1^Taily/KO, and Katnb1 germ cell specific KO (Katnb1^GCKO/GCKO) mice.

Spermatogenesis was abnormal in all KATNB1 LOF models. In the new Katnb1^Taily/KO and Katnb1^GCKO/GCKO models however, more severe and additional phenotypes emerged. Reductions in spermatogenic output scaled with KATNB1 expression, with complete KATNB1 LOF being incompatible with germ cell survival and sperm production (59.9% reduction in Katnb1^Taily/Taily daily sperm output, 83.6% in Katnb1^Taily/KO, and 91.9% in Katnb1^GCKO/GCKO). The reduced Katnb1^Taily/Taily spermatogenic output was due to spermatocytes stalling in anaphase and cytokinesis, resulting in fewer spermatids. In Katnb1^Taily/KO and Katnb1^GCKO/GCKO however the points of germ cell loss were multi-fold and included loss due to catastrophic defects in meiosis and spermatid remodelling, and premature germ cell sloughing from the disordered seminiferous epithelium. Notably, Katnb1^Taily/KO and Katnb1^GCKO/GCKO meiosis frequently failed in metaphase, as well is in anaphase and cytokinesis, due to defects in spindle architecture and dynamics. During haploid germ cell development, more severe loss of KATNB1 function resulted in defects in acrosome biogenesis principally due to abnormal vesicle trafficking. Concomitantly, ectopic vesicles accumulated within the sperm tails of all KATNB1 LOF models, suggestive of intraflagellar transport defects. All KATNB1 LOF models also exhibited abnormal sperm head shaping due to dysregulation of the manchette and, in Katnb1^Taily/KO, the Sertoli cell cytoskeleton. Collectively, this study establishes KATNB1 as a master microtubule-severing regulator during spermatogenesis, required for the regulation of almost all microtubule-based structures.