Phylogenetic Differences in Mouse and Human Motor Neuron Development

About This Grant

Human induced pluripotent stem cell (hiPSC) differentiation offers a unique perspective on species- specific aspects of neuronal development. We employed high-temporal resolution single-cell expression analysis to investigate the mechanisms underlying prolonged and enhanced neurogenesis in the human spinal cord compared to mice. Canonical correlation analysis revealed "human-specific" progenitor clusters marked by early co-expression of NKX2-2 and OLIG2. Lineage tracing revealed that these cells are bone fide motor neuron progenitors. Unlike classical motor neuron progenitors (pMNs), these more ventral motor neuron progenitors (vpMNs) exhibit increased NOTCH and WNT activity, generating motor neurons in a delayed and protracted manner. Furthermore, vpMNs undergo more rounds of cell division, yielding approximately five times more motor neurons that are enriched in motor neuron subtype innervating limbs. Evolution of a new progenitor domain is a novel mechanism through which human CNS increases its size and complexity, distinct from transit amplifying progenitors described in the developing human neocortex. Our proposed research aims to answer four outstanding questions: 1) Is NKX2-2 expression both necessary and sufficient to activate the vpMN program, leading to extended motor neuron genesis? 2) What evolutionary changes in the OLIG2 regulatory system allow human-specific co-expression of OLIG2 and NKX2-2? 3) Does increased NOTCH signaling observed in vpMNs contribute to their specification and delayed neurogenesis? 4) Do vpMNs and pMNs generate different subtypes of motor neurons during human neurogenesis? Addressing these questions will provide valuable insights into the molecular and cellular mechanisms that contribute to the increased number and complexity of motor neurons produced during the human spinal cord development. These insights might lead to improved motor neuron disease models that recapitulate more faithfully human pathology.