Sperm Head–Tail Coupling Apparatus Diversity and Common Themes Among Species

BACKGROUND: A stable connection between the sperm head (containing the nucleus and acrosome) and tail (containing the axoneme, mitochondrial sheath, and periaxonemal structures) is critical for fertility. This connection is mediated by a series of nuclear, cytoplasmic, and centriole components that make up the head-tail coupling apparatus (HTCA). Impairment of the HTCA leads to a severe type of infertility called acephalic spermatozoa syndrome, where sperm heads become detached from their tails. Acephalic spermatozoa syndrome can be found in species across the animal kingdom from flies to humans. OBJECTIVE: Here, we review the literature on HTCA establishment and final HTCA architecture in mature sperm in different species, focusing on common themes throughout. DISCUSSION: Despite a large diversity of sperm structures and HTCA linkages in different species, we propose that there are significant commonalities and underlying themes that shape the HTCA throughout the animal kingdom. In particular, we emphasize the role of centrioles in mediating linkage between the head and tail. CONCLUSION: Given that the molecular architecture of the HTCA is poorly understood, focusing on commonalities of HTCA structure and development is important for extrapolating data from model organisms to combat human infertility.