Widespread haploid-biased gene expression enables sperm-level natural selection.

Area of Science:

• Genetics
• Reproductive Biology
• Evolutionary Biology

Background:

• Sperm are haploid cells requiring functional equivalence for equal allele distribution.
• Gene products are typically shared via spermatid cytoplasmic bridges to equalize sperm phenotypes.
• Unequal distribution of genetic material can disrupt Mendelian inheritance.

Purpose of the Study:

• To investigate the sharing patterns of gene products across mammalian spermatid cytoplasmic bridges.
• To identify genes that are not completely shared and characterize their behavior.
• To explore the evolutionary implications of unequal gene sharing in sperm.

Main Methods:

• Analysis of gene product distribution in mammalian sperm.
• Identification and classification of "genoinformative markers" (GIMs).
• Population genetics analysis to assess allele spread of GIMs in murine, bovine, and human populations.

Main Results:

• A significant class of mammalian genes are not fully shared across spermatid cytoplasmic bridges.
• A subset of these "genoinformative markers" (GIMs) function as selfish genetic elements, promoting uneven allele transmission.
• GIMs are enriched for testis-specific expression, paralogs, and isoforms, suggesting evolutionary pressure related to sperm-somatic function conflict.

Conclusions:

• Genoinformative markers (GIMs) represent a novel class of genes with implications for inheritance.
• Sperm-level selection acting on GIMs may explain unique gene expression patterns observed in testes.
• The discovery of GIMs provides new insights into the evolution of reproductive systems and genetic transmission.