Chromosomal rearrangements as a source of new gene formation in Drosophila yakuba

TL;DR

This study demonstrates that chromosomal rearrangements in Drosophila yakuba can directly create new genes by combining existing gene regions with untranscribed sequences, providing a rapid mechanism for gene evolution.

Contribution

It reveals a novel mechanism of de novo gene formation through chromosomal rearrangements, bypassing intermediate non-coding stages.

Findings

52 de novo genes formed by rearrangements in 14 strains

Rearrangements frequently involve the X chromosome

Gene expression changes observed in 134 existing genes

Abstract

The origins of new genes are among the most fundamental questions in evolutionary biology. Our understanding of the ways that new genetic material appears and how that genetic material shapes population variation remains incomplete. De novo genes and duplicate genes are a key source of new genetic material on which selection acts. To better understand the origins of these new gene sequences, we explored the ways that structural variation might alter expression patterns and form novel transcripts. We provide evidence that chromosomal rearrangements are a source of novel genetic variation that facilitates the formation of de novo genes in Drosophila. We identify 52 cases of de novo gene formation created by chromosomal rearrangements in 14 strains of D. yakuba. These new genes inherit transcription start signals and open reading frames when the 5' end of existing genes are combined with previously untranscribed regions. Such new genes would appear with novel peptide sequences, without the necessity for secondary transitions from non-coding RNA to protein. This mechanism of new peptide formations contrasts with canonical theory of de novo gene progression requiring non-coding intermediaries that must acquire new mutations prior to loss via pseudogenization. Hence, these mutations offer a means to de novo gene creation and protein sequence formation in a single mutational step, answering a long standing open question concerning new gene formation. We further identify gene expression changes to 134 existing genes, indicating that these mutations can alter gene regulation. Population variability for chromosomal rearrangements is considerable, with 2368 rearrangements observed across 14 inbred lines. More rearrangements were identified on the X chromosome than any of the autosomes, suggesting the X is more susceptible to chromosome alterations.