The Prmt5-Vasa module is essential for spermatogenesis in Bombyx mori

Area of Science:

• Developmental Biology
• Genetics
• Insect Reproduction

Background:

• Lepidopteran insects produce two sperm types: eupyrene (nucleated) and apyrene (anucleated).
• Eupyrene sperm fertilize eggs, while apyrene sperm aid eupyrene sperm migration.
• The role of Prmt5 and Vasa in lepidopteran spermatogenesis, particularly in Bombyx mori, remains understudied.

Purpose of the Study:

• To investigate the functional roles of BmPrmt5 and BmVasa in Bombyx mori spermatogenesis.
• To elucidate the regulatory mechanisms underlying dichotomous spermatogenesis in this model organism.

Main Methods:

• CRISPR/Cas9 gene editing to create BmPrmt5 and BmVasa loss-of-function mutants.
• Immunofluorescence staining to analyze sperm morphology.
• Mass spectrometry to identify protein modifications.
• RNA-sequencing (RNA-seq) to analyze gene expression.

Main Results:

• Loss-of-function mutations in BmPrmt5 and BmVasa resulted in male and female sterility.
• Mutants exhibited severe defects in sperm morphology.
• BmPrmt5 regulates the symmetrical dimethylation of BmVasa at specific arginine residues (R35, R54, R56).
• Mutations led to reduced expression of spermatogenesis-related genes, including BmSxl, suggesting a downstream regulatory role.

Conclusions:

• BmPrmt5 and BmVasa are essential and functionally integrated components of the regulatory module controlling spermatogenesis in Bombyx mori.
• BmSxl acts downstream of BmPrmt5 and BmVasa, playing a role in apyrene sperm development.
• These findings provide critical insights into the genetic regulation of sperm dimorphism in insects.