Togaram Ensures Axial Alignment of the Sperm Neck

ABSTRACT The sperm neck must remain mechanically stable to preserve a straight head-tail axis during spermiogenesis, yet the mechanisms that maintain this alignment after head-tail attachment forms are poorly understood. Here, using Drosophila, we identify Togaram (Toga), the ortholog of mammalian TOGARAM1, as a regulator of this maintenance phase. Toga localizes to the sperm neck and to a broader perinuclear microtubule scaffold that surrounds the nucleus, which we term the Sperm Microtubule Cage (SMC). Depletion of Toga causes a striking off-axis phenotype in which the centriole usually remains attached to the nucleus but fails to maintain a straight head-tail axis, whereas complete detachment is comparatively rare. Live imaging shows that this defect arises after initial attachment has formed, indicating a maintenance defect rather than a failure of head-tail assembly. Mechanistically, Toga is dispensable for initial formation of head and neck microtubules but is required for their stabilization during Canoe-stage remodeling. Loss of Toga increases microtubule turnover, strongly reduces acetylated tubulin in the manchette, SMC, and neck region, and leaves the sperm neck vulnerable to buckling. Off-axis spermatids are depleted at later stages, consistent with selective loss of mechanically compromised cells. Finally, Cep104 and CCDC66 associate with Toga in cultured cells and are likewise required for axial alignment, consistent with a conserved module analogous to the mammalian ciliary tip module. Together, these findings support a model in which Toga stabilizes sperm head and neck microtubules to preserve a straight head-tail axis during the maintenance phase of spermiogenesis. Competing Interest Statement The authors have declared no competing interest.