Microtubule structures and dynamics drive many key processes during spermatogenesis, however, their regulation during spermatogenesis remains poorly understood. Here, we sought to investigate the role of spastin, a microtubule-severing enzyme that is yet to be explored during spermatogenesis but was preliminarily reported to be essential for male fertility in mice.
Using a SpastKO/KO mouse model, we reveal that spastin loss resulted in complete absence of functional sperm. We show spastin plays a critical role in the assembly and function of the meiotic spindle, and in its absence, spermatocytes frequently stalled at metaphase and anaphase and germ cell apoptosis was significantly increased. Spastin has previously been identified as essential for the poleward movement of chromosomes during mitosis. Consistent with an essential role for spastin in chromosome segregation, of the round spermatids that were produced in SpastKO/KO mice their nuclei were frequently abnormally large. During spermiogenesis, our data reveals essential roles for spastin in regulating acrosome development. In SpastKO/KOmice we observed the mis-trafficking of pro-acrosomal vesicles resulting in the formation of supernumerary acrosomes. Additionally, we observed extreme abnormalities in manchette structure, characterised by abnormally long and dense manchettes that failed to shape the nucleus. This indicates an essential role spastin in pruning the microtubules of the manchette. Finally, we found that loss of nuclear integrity occurred, leading to increased DNA damage and the vast majority of spermatids becoming pyknotic and dying. The loss of nuclear integrity is likely due to failure to remove microtubules that cross the nuclear envelope as it reforms following meiosis, a role that requires interactions with the ESCRT-III machinery.
Our results demonstrate multiple novel and essential roles for spastin in spermatogenesis and together with our previous data, reveals that the testis requires a ‘toolbox’ of different microtubule severing enzymes each of which have unique subspecialised roles.