Exploring the function of CRY and its transcriptomic context in Drosophila melanogaster

The circadian clock is an essential mechanism regulating many aspects of our life, from a cellular scale to our behaviours. The fruit fly Drosophila melanogaster has been pivotal in understanding the molecular architecture of animal clocks, which share a common evolutionary origin. The first gene discovered in 1971 was period. A mutagenesis screening followed, identifying more genetic component of the clock. The success of that approach opened the gates to a flood of screenings, which in the ’90s and early 2000s resulted in the identification of the main components of the clock in flies, and, largely through homology, in mammals.

This thesis further investigates the molecular clock on a bio-informatic aspect combined with an experimental approach. The publication of a RNAseq dataset in 2017 by Abruzzi et al. set the base for the analysis of the difference in transcriptomes between three groups of clock neurons. A set of genes of interest was isolated for each group of clock neurons. Their effect on the circadian clock was then tested experimentally. A second dataset published in 2021 by Ma et al. enabled to focus the analysis on cry and its cellular context. The single-cell RNAseq technique enable the analysis of each cell individually. By comparing cry-positive and cry-negative clusters, we could study the differences in function enrichment between the two groups. We could also explore new transcription factors that could possibly regulate the expression of cry. Finally, we used point mutations on specific potential active sites of CRY in order to test their effect on CRY’s function in different groups of clock neurons. Some of the mutations induced a long period when expressed in certain groups of clock neurons. The link between the mutations and the phenotypes observed still need more testing to be fully understood.