The proximal centriole-like structure maintains nucleus-centriole architecture in sperm.

Proper connection between the sperm head and tail is critical for sperm motility and fertilization. Head-tail linkage is mediated by the Head-Tail Coupling Apparatus (HTCA), which secures the axoneme (tail) to the nucleus (head). However, the molecular architecture of the HTCA is poorly understood. Here, we use Drosophila to investigate formation and remodeling of the HTCA throughout spermiogenesis by visualizing key components of this complex. Using structured illumination microscopy, we demonstrate that key HTCA proteins Spag4 and Yuri form a 'Centriole Cap' that surrounds the centriole (or Basal Body) as it invaginates into the surface of the nucleus. As development progresses, the centriole is laterally displaced to the side of the nucleus while the HTCA expands under the nucleus, forming what we term the 'Nuclear Shelf.' We next show that the proximal centriole-like (PCL) structure is positioned under the Nuclear Shelf, functioning as a critical stabilizer of centriole-nuclear attachment. Together, our data indicate that the HTCA is a complex, multi-point attachment site that simultaneously engages the PCL, the centriole, and the nucleus to ensure proper head-tail connection during late-stage spermiogenesis.

The Proximal Centriole-Like Structure Anchors the Centriole to the Sperm Nucleus.

Proper connection between the sperm head and tail is critical for sperm motility and fertilization. The link between the head and tail is mediated by the Head-Tail Coupling Apparatus (HTCA), which secures the axoneme (tail) to the nucleus (head). However, the molecular architecture of the HTCA is not well understood. Here, we use Drosophila to create a high-resolution map of proteins and structures at the HTCA throughout spermiogenesis. Using structured illumination microscopy, we demonstrate that key HTCA proteins Spag4 and Yuri form a 'Centriole Cap' that surrounds the centriole (or Basal Body) as it is inserted, or embedded into the surface of the nucleus. As development progresses, the centriole is laterally displaces to the side of the nucleus, during which time the HTCA expands under the nucleus, forming what we term the 'Nuclear Shelf.' We next show that the proximal centriole-like (PCL) structure is positioned under the Nuclear Shelf and functions as a critical stabilizer of the centriole-nuclear attachment. Together, our data indicate that the HTCA is complex, multi-point attachment site that simultaneously engages the PCL, the centriole, and the nucleus to ensure proper head-tail connection during late-stage spermiogenesis.