Transcriptional Dynamics of Motor Neuron Maturation in vivo and in vitro

Mouse spinal motor neurons are specified in the embryo on embrynic day 9.5 (E9.5), but motor function doesn't fully mature till the third week of postnatal life (P14-P21) and the degenerative disease Amyotrophic Lateral Sclerosis only affects motor neurons in adulthood (age of onset differs between models). In order to better understand motor neuron maturation, we have generated a temporal map of motor neuron transcriptional states at E10.5, E13.5, P4, P13, P21, P56, 2yr. In addition we have also profiled stem cell derived motor neurons that were co-cultured with astrocytes at DIV0, DIV7, DIV28. We performed RNA-seq and ATAC-seq on motor neurons or motor neuron nuclei at all in vivo and in vitro timepoints. In vivo mouse motor neurons were purified at E10.5 from HB9-GFP mice by dissociating and FACs sorting for GFP+ motor neuorns. At E13.5-2yr, motor neuron nuclei were purified from Chat-Cre;SUN1-gfp-myc mice. For in vitro experiments, embryonic stem cells were derived from Chat-Cre;SUN1-gfp-myc mice, differentiated into motor neurons and co-cultured with astrocytes. Nuclei were purified at DIV0 (before co-culture), DIV7, and DIV28. In addition, to understand the role of activity in controlling gene expression, motor neurons were co-cultured with astrocytes for 28 days in the presence of TTX.