# Adaptive Evolution and Functional Differentiation of Testis-Expressed Genes in Theria

## TL;DR

This study explores how testis-expressed genes evolved differently in marsupials and placental mammals, identifying genes unique to each group and highlighting adaptive changes in placental mammals.

## Contribution

The study identifies marsupial- and eutherian-specific testis-expressed genes and reveals adaptive evolution in eutherians, particularly in ARHGAP28.

## Key findings

- 22 testis-expressed genes are marsupial-specific, suggesting acquisition after divergence from eutherians.
- 15 testis-expressed genes are therian-specific, with three evolving faster in eutherians.
- ARHGAP28 shows adaptive evolution in eutherians, linked to expression pattern differentiation.

## Abstract

A transcriptome landscape of therian mammals is known, but it remains unclear how transcriptomic patterns have evolved in a marsupial- or eutherian-specific way. It is important to understand marsupial- or eutherian-specific transcriptomic patterns since their fitness and sex differentiation are different. This study examines therian testis transcriptomes to elucidate marsupial and eutherian uniqueness in male differentiation. Using the massive transcriptomic data, we show the evolutionary tempo and mode of testis-expressed genes in Theria and identify candidate genes involved in the specificity of marsupial or eutherian testes.

Gene expression patterns differ in different tissues, and the expression pattern of genes in the mammalian testis is known to be extremely variable in different species. To clarify how the testis transcriptomic pattern has evolved in particular species, we examined the evolution of the adult testis transcriptome in Theria using 10 species: two marsupials (opossum and Tasmanian devil), six eutherian (placental) mammals (human, chimpanzee, bonobo, gorilla, rhesus macaque, and mouse), and two outgroup species (platypus and chicken). We show that 22 testis-expressed genes are marsupial-specific, suggesting their acquisition in the stem lineage of marsupials after the divergence from eutherians. Despite the time length of the eutherian stem lineage being similar to that of the marsupial lineage, acquisition of testis-expressed genes was not found in the stem lineage of eutherians; rather, their expression patterns differed by species, suggesting rapid gene evolution in the eutherian ancestors. Fifteen testis-expressed genes are therian-specific, and for three of these genes, the evolutionary tempo is markedly faster in eutherians than in marsupials. Our phylogenetic analysis of Rho GTPase-activating protein 28 (ARHGAP28) suggests the adaptive evolution of this gene in the eutherians, probably together with the expression pattern differentiation.