Evidence for de novo evolution of testis-expressed genes in the Drosophila yakuba/Drosophila erecta clade

Abstract

The mutational origin and subsequent evolution of de novo genes, which are hypothesized to be genes of recent origin that are not obviously related to ancestral coding sequence, are poorly understood. However, accumulating evidence suggests that such genes may often function in male reproduction. Here we use testis-derived expressed sequence tags (ESTs) from Drosophila yakuba to identify genes that have likely arisen either in D. yakuba or in the D. yakuba/D. erecta ancestor. We found several such genes, which show testis-biased expression and are often X-linked. Comparative data indicate that three of these genes have very short open reading frames, which suggests the possibility that a significant number of testis-biased de novo genes in the D. yakuba/D. erecta clade may be noncoding RNA genes. These data, along with previously published data from D. melanogaster, support the idea that many de novo Drosophila genes function in male reproduction and that a small region of the X chromosome in the melanogaster subgroup may be a hotspot for the evolution of novel testis-biased genes.

Figure 1.—

Gene organization. Exons and introns are indicated by black boxes and horizontal lines, respectively. Putative start and stop codons are indicated by vertical tick marks on exons. Two potential start and stop codons are indicated for gene 52b02.

Figure 2.—

RT–PCR results from various tissues of D. yakuba line Tai18E2. a, accessory gland; b, testis; c, reproductive tract remainder; d, male carcass; e, whole female; f, genomic DNA. Ladder, 1 kb ladder.