A Conserved Requirement for Fbxo7 During Male Germ Cell Cytoplasmic Remodeling

Area of Science:

• Reproductive Biology
• Cell Biology
• Molecular Genetics

Background:

• Fbxo7 is crucial for mitophagy, proteasome activity, and cell cycle regulation.
• Known Fbxo7 roles include Parkinsonian and hematopoietic phenotypes.
• Fbxo7 is a substrate-recognition subunit of an SCF-type ubiquitin E3 ligase complex.

Purpose of the Study:

• To investigate the role of Fbxo7 in male fertility.
• To characterize the cellular mechanisms underlying sterility in Fbxo7-deficient male mice.
• To explore the conservation of Fbxo7 function in spermiogenesis across species.

Main Methods:

• Generation and analysis of male mice with reduced Fbxo7 expression.
• Histological examination of testicular tissues during spermiogenesis.
• Comparison with the Drosophila Fbxo7 ortholog (nutcracker) model.
• Analysis of PI31 levels and proteasome activity in testes.

Main Results:

• Male mice with reduced Fbxo7 expression are sterile.
• Developing spermatids are phagocytosed by Sertoli cells during late spermiogenesis.
• No symplast formation or cell sloughing observed, suggesting novel cell death/disposal mechanisms.
• Reduced PI31 levels observed in mutant mice, but overall proteasome activity in testes remains unaltered.
• Fbxo7 deficiency leads to sterility in Drosophila, linked to decreased DmPI31 and proteasome activity.

Conclusions:

• Fbxo7 is essential for male fertility, specifically during late spermiogenesis.
• The sterility phenotype in Fbxo7 mutant mice involves spermatid phagocytosis and potentially novel cell death pathways.
• Fbxo7 regulates PI31 protein levels, and defects in proteasome dynamics during spermiogenesis may cause infertility.
• The requirement for Fbxo7 in spermiogenesis is conserved between mice and Drosophila.