General and cell-type-specific aspects of the motor neuron maturation transcriptional program

Building a nervous system is a protracted process that starts with the specification of individual neuron types and ends with the formation of mature neural circuits. The molecular mechanisms that regulate the temporal progression of maturation in individual cell types remain poorly understood. In this work, we have mapped the gene expression and chromatin accessibility changes in mouse spinal motor neurons throughout their lifetimes. We found that both motor neuron gene expression and putative regulatory elements are dynamic during the first three weeks of postnatal life, when motor circuits are maturing. Genes that are up-regulated during this time contribute to adult motor neuron diversity and function. Almost all of the chromatin regions that gain accessibility during maturation are motor neuron specific, yet a majority of the transcription factor binding motifs enriched in these regions are shared with other mature neurons. Collectively, these findings suggest that a core transcriptional program operates in a context-dependent manner to access cell-type-specific cis-regulatory systems associated with maturation genes. Discovery of general principles governing neuronal maturation might inform methods for transcriptional reprogramming of neuronal age and for improved modelling of age-related neurodegenerative diseases.