GSE138028
Chromatin environment and cellular context specify compensatory activity of paralogous MEF2 transcription factors
Compensation among paralogous transcription factors (TFs) confers genetic robustness of cellular processes. Despite the prevalence of this phenomenon, an in vivo genome-scale understanding of how TFs dynamically respond to paralog depletion is still needed. We explore this question in the mammalian brain by studying the highly conserved MEF2 family of TFs, which confer phenotypic robustness in multiple brain regions. Employing single and double conditional knockout of MEF2A and MEF2D in granule neurons of the mouse cerebellum, we find MEF2A and MEF2D play functionally redundant roles in cerebellar-dependent motor learning. To explore the molecular basis underlying this phenomenon, we systematically characterize in vivo genome-wide occupancy of MEF2A and MEF2D in the presence or absence of one another. Although highly co-expressed in granule neurons, MEF2D is the predominant genomic regulator of gene expression. Strikingly, upon depletion of MEF2D, the occupancy of MEF2A robustly increases at a subset of sites normally bound to MEF2D. Epigenome and transcriptome analyses reveal that sites experiencing compensatory MEF2A occupancy undergo functional compensation for genomic activation and gene expression. In contrast, a distinct population of sites without compensatory MEF2A activity undergo significant dysregulation upon loss of MEF2D. The two populations of MEF2 target sites are further stratified by relative chromatin accessibility, with compensatory MEF2A activity concentrated within more open chromatin. Finally, we reveal that motor activity-induced changes in neuronal state induce a dynamic switch from non-compensatory to compensatory MEF2-dependent gene regulation, demonstrating the context-dependent nature of paralogous TF interdependency. Collectively, these studies define the first in vivo genome-wide characterization of functional interdependency between paralogous TFs. Overall design: Examination of interdependency of MEF2A and MEF2D via transcriptomic and epigenomic characterization in control and conditional knockout mammalian cells.