Transcriptomic profiles of the maternal-to-zygotic transition for Drosophila embryos exposed to acute and chronic heat stress.

Heat stress challenges embryo survival, but the molecular reasons for this are unclear. We investigated how heat stress alters the maternal-to-zygotic transition (MZT) during Drosophila melanogaster development. Using RNA sequencing, we characterized the MZT under nonstress, acute, and chronic heat stress conditions. MZT genes were defined as those differentially expressed between the minor and major waves of zygotic genome activation. MZT genes were associated with multiple processes, including transcription, splicing, translation, and development. Under acute stress, the MZT deviated little from nonstressed embryos except that heat shock protein (HSP) genes were activated, and maternal transcript clearance was minimally misregulated. Under chronic stress, a core MZT persisted; but stress-related gene expression was obvious, maternal transcripts were strongly misregulated, and embryos showed poor survival. Overall, the MZT is robust, but increasingly falters with more severe stress. We present our dataset as a resource to aid molecular understanding of embryo resilience and vulnerability to environmental stressors.