Asymmetric interactions between doublesex and tissue- and sex-specific target genes mediate sexual dimorphism in beetles

C C Ledón-Rettig,E E Zattara,A P Moczek

doi:10.1038/ncomms14593

Abstract

Sexual dimorphisms fuel significant intraspecific variation and evolutionary diversification. Yet the developmental-genetic mechanisms underlying sex-specific development remain poorly understood. Here, we focus on the conserved sex-determination gene doublesex (dsx) and the mechanisms by which it mediates sex-specific development in a horned beetle species by combining systemic dsx knockdown, high-throughput sequencing of diverse tissues and a genome-wide analysis of Dsx-binding sites. We find that Dsx regulates sex-biased expression predominantly in males, that Dsx's target repertoires are highly sex- and tissue-specific and that Dsx can exercise its regulatory role via two distinct mechanisms: as a sex-specific modulator by regulating strictly sex-specific targets, or as a switch by regulating the same genes in males and females in opposite directions. More generally, our results suggest Dsx can rapidly acquire new target gene repertoires to accommodate evolutionarily novel traits, evidenced by the large and unique repertoire identified in head horns, a recent morphological innovation.

Highlights

Sexual dimorphisms fuel significant intraspecific variation and evolutionary diversification
The majority of genes exhibiting sex-biased expression were found in genital tissue (85% and 67% of genes with female- and male-biased expression, respectively), with the largest proportion of sexbiased gene expression occurring uniquely in head horn tissue (8% and 26% of genes with female- and male-biased expression, respectively)
We found that (i) Dsx has a central role in generating sex-biased gene expression by both activation and suppression of gene expression; (ii) whereas Dsx modulates sex-biased gene expression across several male tissues, its role in homologous female tissues is mostly restricted to head horn tissue; and (iii) the target repertoire of Dsx in head horns is unique in that it is both exceptionally large relative to the other tissues assessed, and because some of these targets are shared between males and females—albeit modulated in opposite directions—whereas targets among other tissues are largely sex-specific

Summary

Introduction

Sexual dimorphisms fuel significant intraspecific variation and evolutionary diversification. We characterize the target repertoire of Dsx across four different tissues of males and females of the bull-headed dung beetle Onthophagus taurus, a species whose body regions express various degrees of morphological sexual dimorphism, and which is amenable to both genome-wide transcriptomic profiling and gene function analysis. Our approach in this study employed the functional knockdown of O. taurus male and female dsx mRNA isoforms[14] by injection of a double stranded (dsRNA) construct (OtdsxC) targeting a region common to all isoforms, followed by genomewide analyses of gene expression across brains, genitalia, thoracic horns and head horns, and paralleled by an analysis of predicted Dsx-binding sites across the O. taurus genome This approach allowed us to characterize putative Dsx target repertoires in an unbiased fashion, across diverse tissues, and at a genome-wide level. We discuss our results in the light of the different evolutionary histories of male and female Dsx isoforms and the evolutionary lability of sexual dimorphisms across lineages

Methods

Results

Conclusion