Gubala AM, Schmitz JF, Kearns MJ, Vinh TT, Bornberg-Bauer E, Wolfner MF, Findlay GD
The goddard and saturn genes are essential for Drosophila male fertility and may have arisen de novo
Molecular Biology and Evolution, 2017

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Abstract

Gene duplication has long been considered the major evolutionary process that gives rise to new, lineage-specific genes. However, recent research in Drosophila and other taxa suggests that de novo evolved genes are also an important source of evolutionary novelty. De novo genes arise from non-protein-coding DNA at a surprisingly high rate, and their expression is often restricted to the male germline. Previous studies have attempted to use organism-wide RNA interference to infer the function of such genes, but the interpretation of these results has been complicated by technical issues. We have characterized two putative de novo evolved genes, goddard and saturn, that we show to be essential for spermatogenesis and sperm function in D. melanogaster. Both genes likely arose at the base of the Drosophila genus, have been lost in certain lineages, and show conserved, male-specific patterns of expression. All species with goddard have a single copy of the gene, which shows signatures of purifying selection. In contrast, saturn has diversified in certain lineages through gene duplication or positive selection. Depletion of either gene by testis-specific RNAi in D. melanogaster leads to severe fertility defects: goddard knockdown males fail to produce any sperm, while saturn knockdown males produce fewer sperm that function inefficiently once transferred to females. These data suggest that de novo genes may play essential roles in shaping the evolution of male reproductive traits