Revealing the transcriptional control of patterned cell death within developing neural networks

Nervous systems are the most extraordinarily complex structures we know of. During development neural stems cells divide to give rise to a myriad of different neuron types that wire together generating functional, interconnected neural networks. The insect central nervous system is largely built from a segmentally repeated, stereotyped array of neuronal stem cells, called neuroblasts, that make distinct families or ‘lineages’ of neurons. Neuroblasts divide repeatedly, generating pairs of A and B neurons, that form two ‘hemilineages’. Soon after neurons are born these hemilineage modules show distinct patterns of gene expression that define key characteristics, such as, the neurotransmitter it uses, how it grows and critically whether that neuron lives or dies. Programmed cell death appears to be a universal mechanism deployed during the development of nervous systems. In our previous work we discovered that death is a common fate within hemilineages, of the ventral nerve cord, dictating the type and number of neurons available for building circuits later in development. Insect models provide a great opportunity to gain deep insights into the molecular mechanisms controlling early fate decisions, like death. Our conjecture is that the control of this precisely patterned hemilineage-specific death by the ‘pro-death’ genes, reaper and grim is governed by two aspects of regulation. Firstly, that there are specific combinations of transcription factors (TFs), that bind DNA and control transcription of genes, in distinct doomed hemilineages. Secondly, that lineage-based differences in chromatin accessibility allow transcription factors to bind when open or not bind when closed. Our specific objectives are: Identify hemilineage-specific TFs and chromatin accessibility landscapes within doomed thoracic hemilineages using single cell multi-omics. Test the requirement of cis-regulatory elements within the reaper/grim locus and the contribution of individual TFs for hemilineage-specific patterns of Reaper and Grim transcription using CRISPR As frontier bioscience this project will explore the ‘rules of life’. The knowledge generated will give valuable insights into how complex patterns of gene expression are orchestrated at these early stages of development, when many properties of a neurons ‘character’ are set in place. The questions and state-of-the-art approaches will provide excellent training for the next generation of bench scientists. Revealing these rules of ‘hemilineage development’ will complement recent advances that have been made in decoding the thoracic circuits of Drosophila using EM-based connectomics. Furthermore, our work will generate a suite of tools and reagents during this project that will be immensely useful for researchers studying questions of gene regulation, programmed cell death and neurodevelopment. More broadly, insects represent a significant threat to global health and food security, deepening our understanding of their development and physiology remains an important goal in the biosciences. Our hope is that uncovering this fundamental biology in Drosophila will provide insights into the way all nervous systems are built and how some mechanisms can become disrupted in developmental disorders.