Elucidating the role of DLC1 Isoform 1 in Human Motor Neuron Development and Spinal Muscular Atrophy

Abstract

Spinal muscular atrophy (SMA) is a motor neuron (MN) disease caused by loss of the ubiquitously expressed Survival Motor Neuron (SMN) spliceosome protein, resulting in selective degeneration of spinal MNs but the mechanisms underlying the specific loss of MNs remain unknown. A previous report showed that Deleted in Liver Cancer 1 (DLC1) is the most down-regulated gene in MNs derived from a SMA patient but its roles in MN development and SMA pathogenesis remain to be elucidated. Here, we detected a gradually increasing of endogenous DLC1 isoform 1 (DLC1-i1) expression level as human embryonic stem cells differentiated into MN lineage. Knockdown (KD) of DLC1-i1 led to a reduction in MN formation, axonal outgrowth and increase apoptosis, whereas overexpression of DLC1-i1 promoted MN differentiation with extensive axonal outgrowth. Importantly, SMN KD not only caused MN loss but also intron retention of DLC1-i1, resulting in downregulation of DLC1-i1 expression. We also confirmed decreased levels of DLC1-i1 in spinal MNs derived from SMA patients’ urine derived induced pluripotent stem cells compared to healthy individuals, as well as in spinal cord of SMA postnatal mice carrying SMN-/- compared to SMN+/- mice. Altogether, our results indicate that DLC1-i1 plays an important role in MN differentiation especially axonal extension and deficiency of SMN causes selective loss of MN partly through disruption of DLC1-i1 splicing.