Proteasomal Gene Duplications And Recruitment Of Testis Specific Expression In Drosophila

Abstract

Proteasome is a large multisubunit complex that degrades ubiquitinated proteins in a highly regulated manner in all eukaryotes. Two subcompartments of this subunit are the 19Scap and the 20S core particle with 19S acting as regulatory subunit, it attaches at both ends of the 20Score particle harboring the catalytic domains. In D. melanogaster one third of the genes encoding for this subunit were recognized to have many male specific duplicates. In this work, we make use of the new 12 genomes sequences and show that the majority of the genes encoding for the 20S particle gave rise to at least one functional duplicate mainly through retroposition in the past 60 My. Using evolutionary data, we estimated the rate of evolution of 3 of the retrocopies and compared them to their parental genes. They all evolve faster than the parental genes which could be explained by relaxation of constraint or positive selection. Additional data is needed to discern between these alternatives. We study the expression of pros28.1A, a gene known to have testis specific expression in D. melanogaster, in D. simulans and D. yakuba. In these species we reveled that pros28.1A is transcribed in a male specific pattern using different transcription start site. In an effort to understand the motif/s that drive this testis specific expression, we experimentally study the regulatory region of pros28.1A in D. melanogaster. Originated through retroposition event via an mRNA intermediate, pros28.1A and retrogenes alike usually lack the regulatory sequences. Thus, in order to be transcribed, they must recruit new promoters. Here we show that a short region (i.e. 46bp) very close to the transcription start site of D. melanogaster drives the expression of a reporter gene in testis of transformant flies. However, this region is not likely to drive the testis specific expression of this gene in D. simulans and D. yakuba which have different transcription start site from that of D. melanogaster. This data is in agreement with the previously observed high gene turnover for testis expression in Drosophila.