Spermatogenesis revisited. V. Spermiogenesis in mice homozygous for two different male-sterile mutations (ps and hpy)

Area of Science:

• Reproductive Biology
• Developmental Biology
• Genetics

Background:

• Male infertility is a significant concern, often stemming from defects in sperm production (spermiogenesis).
• Understanding the genetic basis of spermiogenesis is crucial for diagnosing and treating male infertility.
• Pleiotropic mutations can affect multiple developmental processes, complicating the analysis of gene function.

Purpose of the Study:

• To investigate the combined effects of two recessive mutations, ps (pink-eyed sterile) and hpy (high-penetrance, yellow), on male mouse spermiogenesis.
• To determine if these mutations act independently or interactively during spermatid development.
• To characterize the specific ultrastructural defects caused by each mutation and their combined presence.

Main Methods:

• Generation and analysis of male mice homozygous for both ps and hpy mutations.
• Light and electron microscopy to examine spermatogenesis stages, focusing on spermiogenesis.
• Ultrastructural analysis of sperm components, including centrioles, axonemes, and head morphology.

Main Results:

• Gametogenesis proceeded normally through meiosis, but no functional spermatozoa were formed in double homozygotes.
• Spermiogenesis abnormalities were observed from the Golgi phase onwards.
• Early and mid-stage defects resembled those of the ps mutation, while later-stage defects (axoneme and head abnormalities) were characteristic of the hpy mutation.
• Centriolar ultrastructure was normal, but axonemal structures were rare, and flagella were not recognizable in late spermatids.
• Late spermatids exhibited head abnormalities consistent with either ps or hpy mutations, with no novel phenotypes observed.

Conclusions:

• Each mutation (ps and hpy) appears to act autonomously during spermiogenesis, even when present simultaneously.
• The study supports the independent action of these mutations on distinct sub-processes of spermiogenesis.
• These findings provide insights into the genetic control of sperm development and the lack of interaction between these specific mutations.