Two sexes, one genome: regulatory structure of sex-biased development without sexual chromosomes
Sexual dimorphism poses a challenge for genetically-minded scientists: How can animals with near-identical genomes be so strikingly different? Existing theories rely on selection for sex-linked genes, yet sexual dimorphism is present also in species that lack sexual chromosomes. How do these species induce and maintain different developmental trajectories?
I present the results of my research on the sexual development of the jewel wasp Nasonia vitripennis (Hymenoptera). Nasonia's sex is determined by the number of genome copies received by the zygote and does not show any sex-linked locus within its genome.
I compare the transcriptomes of developing male and female Nasonia in order to detect the mechanistic processes that induce sexual dimorphism throughout development. In particular, I test whether sex-specific differences are present at three molecular levels:
- Sub-gene, via alternative splicing
- Whole-gene, via differential expression
- Between-gene, via higher order transcript-transcript interactions
I show how splicing comprises only a minor portion of between-sex differences, whereas differential expression and sex-biased interactions complement each other and alternate in prevalence throughout development.
Finally, I reconstruct the structural organization of sex-biased developmental sub-networks and compare them to non sex-biased sub-networks. The regulatory architecture of sex-biased sub-networks shows stronger hierarchical organization and preferential integration of new genes in potentially regulatory positions.