Testis-specific fascin component FSCN3 is dispensable for mouse spermatogenesis and fertility.

BACKGROUND: Fascins belong to a family of actin-bundling proteins that are involved in a wide range of biological functions. FSCN3, a newly identified testis-specific actin-bundling protein, is specifically expressed in elongated spermatids. However, its in vivo function in mouse spermiogenesis remains unknown. METHODS AND RESULTS: We generated Fscn3 knockout mice through CRISPR/Cas9 gene-editing technology. Fscn3-/- mice displayed normal testis morphology and testis to bodyweight ratio, and sperm concentrations did not differ significantly between Fscn3+/+ and Fscn3-/- mice. Fertility assays consistently revealed that Fscn3-/- mice are completely fertile and their reproductive status does not differ from that of wild-type. Moreover, hematoxylin and eosin staining of the testis sections of Fscn3-/- mice detected various germ cells, ranging from spermatogonia to mature spermatozoa. Furthermore, the swimming velocity of the sperm of Fscn3-/- mice was comparable to that of their wild-type littermates. Both Fscn3+/+ and Fscn3-/-mice had normal sperm morphology, indicating that the disruption of Fscn3 does not affect sperm morphology. The analysis of meiotic prophase I progression demonstrated normal prophase-I phases (leptonema to diplonema) in both Fscn3+/+ and Fscn3-/- mice, suggesting that Fscn3 is not essential for meiosis I. CONCLUSION: Our study provides the first evidence that FSCN3 is a testis-specific actin-bundling protein that is not required for mouse spermatogenesis. Our results will help reproductive biologists focus their efforts on genes that are crucial for fertility and avoid research duplication.