RNAseq and a fused neo-Z chromosome yields insight into dosage compensation and sex chromosome evolution in Lepidoptera

In diploid species, there are primarily two types of sex determination systems. The heterogametic sex is male in XX/XY systems and female in ZZ/ZW systems. Since the Y chromosome of XY males and the W chromosome of ZW females are usually degenerate, the dosage of functional sex linked genes is different between two sexes. Dosage compensation is a mechanism to equalize the expression of sex linked genes, thereby ensuring the health of the individuals. Observations and mechanisms of dosage compensation differ between the two systems, and at present most studies have focused on XX/XY system, leaving the ZZ/ZW world poorly understood. Among insects, the sibling orders of Lepidoptera and Trichoptera stand out as the only orders having the ZZ/ZW system.  In this presentation, I will describe investigations of dosage compensation in the codling moth, Cydia pomonella, a species belonging to a phylogenetically basal group, Tortricidae, with an unusual neo-Z sex chromosome that originated from translocation of an autosome to the ancestral Z chromosome. Using Illumina RNAseq and bioinformatics tools I have analyzed the relative levels of expression of sex-linked and autosomal genes in gonadal tissues of C. pomonella males and females, shedding light on dosage compensation, sex-specific gene expression, and chromosome evolution in the Lepidoptera.