# NSUN7 Regulates Sperm Flagella Formation at All Stages of Spermiogenesis

## TL;DR

This study shows that NSUN7 is crucial for sperm flagella formation during spermiogenesis and its absence leads to male infertility.

## Contribution

The study reveals NSUN7's role in stabilizing protein complexes and coordinating flagellar assembly during all stages of spermiogenesis.

## Key findings

- NSUN7 is most abundant in round spermatids during flagellum and fibrous sheath formation.
- Loss of NSUN7 disrupts proteins involved in dynein arm assembly, intraflagellar transport, and fibrous sheath organization.
- Plectin accumulation may cause impaired cytoplasm retention in elongated spermatids.

## Abstract

Spermiogenesis requires extensive molecular and structural remodeling to produce motile sperm. Mutations in the testis-specific RNA methyltransferase NSUN7 are associated with defective fibrous sheath, impaired sperm motility, and male infertility. However, the underlying molecular mechanisms remain poorly understood. Here, we performed proteomic profiling of sorted, elongated, and round spermatids, as well as mature spermatozoa from Nsun7 knockout mice. We showed that NSUN7 is present at all stages of spermiogenesis and is most abundant in round spermatids, which corresponds to the formation of the flagellum and fibrous sheath assembly. Loss of NSUN7 altered the abundance of proteins essential for dynein arm assembly (PIH1D3, CCDC103, CCDC40), intraflagellar transport (IFT122), and fibrous sheath organization (AKAP3, AKAP4, ROPN1L). We also showed that the previously detected impaired retention of cytoplasm in elongated spermatids may be caused by plectin accumulation. Interestingly, no statistically significant changes were found in mature sperm proteomes upon Nsun7 inactivation. Our findings support a model in which NSUN7 primarily stabilizes protein complexes and coordinates flagellar assembly. This indicates that NSUN7 is a critical regulator of spermiogenesis, and its malfunction is a contributing factor to male infertility.