PgmNr P2154: Functional divergence of two young duplicate genes in Drosophila.

Authors:
I. M. Ventura 1,2 ; M. Long 1


Institutes
1) Ecology and Evolution, University of Chicago, Chicago, IL; 2) CAPES Foundation, Ministry of Education, Brazil.


Abstract:

New duplicate genes can rapidly diverge from their parental copies in sequence and expression, and acquire novel or specialized functions. Understanding their divergence can shed light on the molecular mechanisms leading to evolutionary innovations. Here, we explore the functional evolution of Zeus and Poseidon (CG2053), two young genes that duplicated from the same parental gene, Caf40, in Drosophila. Caf40 encodes a broadly expressed and highly conserved nucleic acid binding protein in eukaryotes, which is part of a regulatory complex that plays a prominent role in many aspects of transcriptional and translational regulation of many genes. Previous works have shown that Zeus affects the expression of a different set of genes from those regulated by Caf40, and acquired an important role in male fertility. Curiously, we recently found an older Caf40 duplicate, which we call Poseidon, whose evolutionary trajectory resembles Zeus’: both originated through retrotransposition of Caf40, are only expressed in testis and larval imaginal discs, and rapidly diverged in amino acid sequence, exhibiting signals of positive selection. In addition, both duplicates underwent a burst of amino acid replacements shortly after duplication, whereas more recent branches have rates consistent with purifying selection.

Strikingly, we found that many crucial residues that are invariable among Caf40 proteins from distantly related eukaryotes were substituted in Zeus and Poseidon (for instance, respectively 22% and 51% of the totally conserved sites in the Caf40 alignment were replaced in the duplicates), which suggests that fundamental properties of the original protein may have been altered in the young copies. Using RNAi knockdown in D. melanogaster, we also found that silencing Zeus results in a 30% decrease in egg to adult survival compared to controls. The impact on both viability and fertility suggests that the young gene was coopted in different tissues and developmental contexts. We will further test the hypothesis that the duplicate paralogs enrolled in new cellular processes by recruiting new protein partners. In addition, the independent evolution of duplicates of the same parental gene suggests that some molecular properties, such as the ability of engaging in protein interactions, may increase the probability of young genes being retained and evolving new functions.