Rcd-1 Related:a Positively Selected Retrogene With Spermatogenesis Function In Drosophila
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Gene duplication is one of the major forces in driving genome evolution. Our study focuses on a particular retrogene Rcd-1 related (Rcd-1r) that originated through retroposition of the parental gene Required for cell differentiation 1 (Rcd-1) about 5-13 million years ago. Rcd-1r is present in D. melanogaster, D. simulans, D. sechellia and D. mauritiana whereas the parental gene is present in all the Drosophila species. Rcd-1r is inserted in the 3' UTR of the gene CG13102 and it is encoded in the complementary strand. Previous studies by Castrillion et al. showed that a P element inserted in the 5' UTR of Rcd-1r (that it is also the 3' UTR of CG13102) resulted in male sterility. The aim of this study have been to find out which of the two genes CG13102 or Rcd-1r is responsible for the sterility of the P element insertion and to study Rcd-1r molecular evolution. We have studied the quality of the transcripts and quantified the expression of CG13102 and Rcd-1r in both wild type and sterile males. We show that the transcript of CG13102 in testis is not affected in the mutant flies but that Rcd-1r 5'UTR and protein level are affected in mutant males. Given these results we propose that Rcd-1r has a major role in the Drosophila male germline revealed by the P element insertion. We also studied Rcd-1r and Rcd-1 molecular evolution and reveal that the parental gene is under very strong purifying selection and the retrogene is evolving under both purifying and positive selection. McDonald-Kreitman test reveals that many amino acid substitutions have fixed not only to change function of this gene after duplication but after that in every lineage the protein keeps changing fast under positive selection. The evolutionary studies of Rcd-1r suggest that this gene may have a new function. This pattern of evolution is often seen in male germline genes that have functions that are under constant sexual selection or intersexual co-evolution. This would be different from the parental gene function.