Sex-biased gene expression across mammalian organ development and evolution

Area of Science:

• Developmental Biology
• Genomics
• Evolutionary Biology

Background:

• Sexually dimorphic traits are prevalent in mammals, arising from sex-specific developmental programs.
• Understanding these genetic programs is crucial for comprehending developmental biology and evolutionary processes.
• Previous research has limited insight into the dynamics of sex-specific gene expression during development.

Purpose of the Study:

• To investigate the gene expression profiles in males and females across various organs and species during development.
• To identify patterns and timing of sex-biased gene expression.
• To explore the evolutionary dynamics of sex-biased gene expression at both gene and cellular levels.

Main Methods:

• Analyzed gene expression profiles from male and female individuals across five organs in five mammalian species (human, mouse, rat, rabbit, opossum) and one bird (chicken).
• Examined gene expression changes throughout development.
• Compared sex-biased gene expression patterns across different organs, species, and cell types, alongside evolutionary analyses.

Main Results:

• Sex-biased gene expression exhibited significant variation across organs and species, often being cell-type specific.
• Abrupt increases in sex differences were observed around sexual maturity, rather than gradual changes during development.
• Sex-biased gene expression demonstrated rapid evolution at the gene level, with distinct evolutionary mechanisms across organs, but slower evolution at the cellular level, maintaining conserved sexually dimorphic cell types across species.

Conclusions:

• Sex-specific genetic programs are dynamically regulated during development, with significant divergence across species and organs.
• Sexual maturity represents a critical window for the establishment of sex differences in gene expression.
• While gene-level expression evolves rapidly, conserved cell types underlie sexually dimorphic traits across diverse species, highlighting a balance between rapid adaptation and conserved developmental mechanisms.