# Peculiarities of the e(y)2 Gene Evolution in Deuterostomes and Drosophilinae

## TL;DR

The e(y)2 gene evolved differently in Deuterostomes and Drosophilinae, with retroposition leading to functional retrogenes and tissue-specific roles.

## Contribution

The study reveals distinct evolutionary paths of the e(y)2 gene in Deuterostomes and Protostomes through retroposition and functional divergence.

## Key findings

- In Deuterostomes, e(y)2 has multiple functional retrogenes from retroposition events.
- In Drosophila, the retrocopy e(y)2 compensates for the parental gene in most tissues except testes.
- The parental e(y)2b gene in Drosophila is testis-specific and impacts male fertility when knocked out.

## Abstract

Gene duplication, a major source of new genes in evolution, often occurs via reverse transcription of mRNA, leading to the integration of a retrocopy into a new genomic locus. Here, we performed an in-depth analysis of the evolutionary history of the e(y)2 gene in Metazoa. The E(y)2 protein is a shared subunit of two highly conserved complexes involved in transcription regulation (the DUB module of the SAGA complex) and mRNA transport (TREX-2). In Deuterostomes, the e(y)2 gene has undergone multiple independent retropositions, often giving rise to functional retrogenes. In contrast, among Protostomes, duplications of e(y)2 were identified only in Drosophilinae and a member of the Lepidoptera family (Manduca sexta). In Drosophila, the retrocopy e(y)2 acquired an almost ubiquitous expression pattern and compensates for the function of the parental gene in all tissues except the testes. The parental gene, e(y)2b, evolved a testis-specific expression pattern, lost the ability to incorporate into the DUB module, but retained nuclear envelope localization and the capacity to assemble into the TREX-2 complex. Knockout of the D. melanogaster e(y)2b gene resulted in reduced male fertility. Overall, our study highlights distinct evolutionary trajectories of the e(y)2 gene in Deuterostomes and Protostomes.