Characterizing the Maternal-Zygotic Transition in the Haplodiploid Wasp Nasonia

The onset of the maternal-to-zygotic transition (MZT) in animals is dependent upon multiple and variable factors, including maternally deposited transcription factors, DNA methylation, and the nucleocytoplasmic ratio (N/C ratio). While the MZT has been characterized extensively in several model systems, it is unclear how universal the features in those systems are or how the MZT adapts to different genetic systems. To expand the phylogenetic sampling of MZT systems, we have been using the jewel wasp Nasonia. Unlike other models, Nasonia uses a haplodiploid genetic system, where fertilized eggs develop as diploid females and unfertilized develop as haploid males. Also, in contrast to the well-characterized MZT model Drosophila, but similar to most other metazoans, Nasonia has a complete functional DNA methylation toolkit. In this thesis, I functionally characterized the unusual features of the Nasonia MZT. Firstly, the N/C ratio does not appear to play an important role in determining the timing of early embryonic events during the Nasonia MZT. Despite this, key players of the Drosophila MZT, such as Smaug and Zelda, are functionally conserved in Nasonia. Second, I found that a DNA methyltransferase paralog (Nv-dnmt1a) is required for both MZT and global gene body methylation during the MZT Nasonia. Genes that lost DNA methylation in their gene bodies as a result of Nv-dnmt1a knockdown have reduced transcriptional output, suggesting that gene body methylation is required for robust transcription during zygotic genome activation. Previous work in Nasonia showed that sex determination is largely regulated by the MZT. Using previously generated transcriptome datasets; I identified several candidates that may play a role in establishing female fate in Nasonia. Additionally, I performed a parental RNAi screen looking at the function of over 30 sex-specific transcripts and identified several that were either dispensable for embryogenesis or required for oogenesis. I also performed chromatin accessibility assays to identify regulatory regions for important for embryonic patterning and sex determination to be used for putative enhancer studies. This work represents the first set of functional studies that reveal how the MZT has adapted to different genetic systems in insects outside of Drosophila.