Gene regulatory landscape of cerebral cortex folding

Our brains accommodate a largely folded cerebral cortex that associates to our advanced brain functions. Several theories have been proposed to explain the cortical folding process, reasoning the mechanical forces as neuronal tension in underlying layers, cellular expansion and glial progenitor's diversity in the OSVZ; but the mechanistic insights and underlying genomics changes causing the appearance of cortical folds is still illusive. Importantly, no studies have attempted to comprehensively characterize the gene regulatory networks underlying cortical folding during development. Here, by using ferret as a model system, we have compared the transcriptomes of germinal layers between sulci and gyri, of different cortical areas and across two developmental stages (E30 & E34), to achieve a comprehensive understanding of the spatio-temporal dynamics of gene expression of cortical progenitors. Furthermore, we have also characterized the epigenetic landscape of germinal layers at E30 and E34, a critical period for their development, to correlate changes in chromatin at promoter and enhancer regions with the observed changes in gene expression. Our preliminary results indicate towards a clear transformational axis of gene regulation between germinal layers. By performing motif analysis of differentially expressed gene (DEGs), we reveal transcription factors which might have a critical role in determining cortical folding. The genes targeted by these factors belong to important pathways implicated in proliferation and neurogenesis. We highlight potential candidates in cortical folding through functional validation studies and acetylation (H3K27ac) levels for these genes correlate with their expression state. Importantly, these are critical for cell adhesion, migration and proliferation processes in-line with previous studies stating that proliferative divisions cause neocortical expansions. Our findings will have strong impact on the clinical interventions for neurological disorders relating to cortical malformation, while at the same time enhancing our understanding of molecular circuitry underlying gyrencephalic brain development and folding. Overall design: 1. RNA-seq was performed at embryonic day 30 (E30), 34 (E34) in microdissected ferret cortex for gyrus and sulcus regions; 2. H3K27ac (abcam, ab4729) ChIP-seq was performed at embryonic day 30 and 34 in microdissected ferret cortex for gyrus and sulcus regions; 3. E37 ferret embryos previously electroporated at E34 were obtained for scRNAseq library preparation from microdissected ferret cortex.