Gliogenesis in lampreys shares gene regulatory interactions with oligodendrocyte development in jawed vertebrates

Glial cells in the nervous system regulate and support many functions related to neuronal activity. Understanding how the vertebrate nervous system has evolved demands a greater understanding of the mechanisms controlling evolution and development of glial cells in basal vertebrates. Among vertebrate glia, oligodendrocytes form an insulating myelin layer surrounding axons of the central nervous system (CNS) in jawed vertebrates. Jawless vertebrates lack myelinated axons but it is unclear when oligodendrocytes or the regulatory mechanisms controlling their development evolved. To begin to investigate the evolution of mechanisms controlling glial development, we identified key genes required for the differentiation of oligodendrocytes in gnathostomes, including Nkx2.2, SoxE genes, and PDGFR, analyzed their expression, and used CRISPR/Cas9 genome editing to perturb their functions in a primitively jawless vertebrate, the sea lamprey. We show in lamprey that orthologs required for oligodendrocyte development in jawed vertebrates are expressed in the lamprey ventral neural tube, in similar locations where gnathostome oligodendrocyte precursor cells (OPC) originate. In addition, they appear to be under the control of conserved mechanisms that regulate OPC development in jawed vertebrates and may also function in gliogenesis. Our results suggest that although oligodendrocytes first emerged in jawed vertebrates, regulatory mechanisms required for their development predate the divergence of jawless and jawed vertebrates.