Background
The sperm flagellum is a modified motile cilium, essential for male fertility. It provides the motility necessary for sperm to traverse the female reproductive tract and fertilise an ovum. Despite this, the molecular processes essential for its assembly remain poorly defined. Recently, the poorly characterised coiled coil domain containing protein, Testis Expressed 9, TEX9, was identified as a novel centriolar satellite protein and a ciliation factor in human RPE-1 cells (1), as well as a regulator of cilia formation and function in freshwater flatworms (Schmidtea mediterranea) (2). Its mammalian in vivo function, however, remains unknown.
Methods
Given the predominant expression of TEX9 in human and mouse male germ cells, herein, we sought to test its role in spermatogenesis and male fertility using a Tex9 knockout mouse model. Male fertility was assessed through fertility testing, immunofluorescence staining, electron microscopy, and co-immunoprecipitation experiments. For all analyses n ≥ 3 mice/genotype were assessed, and statistical differences were determined using unpaired student’s T-tests with significance defined as p < 0.05.
Results
We reveal TEX9 is essential for male fertility, wherein it is required for flagellum formation during spermiogenesis. Specifically, fertility testing revealed that Tex9 knockout male mice were completely sterile. While knockout mice produced normal numbers of sperm, only 13% of them were able to reach the epididymis, and of those that did, none exhibited progressive motility. Closer examination showed that this was due to severe defects in sperm tail development (p < 0.0001 compared to wildtype). Spermatids exhibited a range of defects including supernumerary centrioles, and failures in basal-body plasma membrane docking, ciliary lobe formation and axoneme extension.
Conclusion
Collectively our data establishes TEX9 as a key regulator of centriole to basal body transition and basal body maturation, and furthers our understanding on the processes essential for functional sperm formation.