Meeting Abstract
The evolution of large body size in animals required the ability to propagate electrical signals rapidly along neurons for long distances. One solution was to increase the diameter of axons thereby increasing conduction velocity. Vertebrates have solved this problem by forming an insulating myelin sheath that surrounds axons and is formed from glial cells. By insulating small diameter axons, the vertebrate brain can accommodate a larger number of neurons, facilitating the complex connections of the vertebrate nervous system. To study the origin of vertebrate myelin, we are investigating gliogenesis in the sea lamprey, Petromyzon marinus. Sea lampreys are basal jawless vertebrates that lack myelinated axons yet they possess supporting glial cells in both the central and peripheral nervous systems (CNS, PNS), making them ideal for investigating the origin of myelin. Our preliminary data show SoxE2 (Sox10) is expressed in the PNS. However, other genes required for myelination in jawed vertebrates (Krox20, POU3) were not detected in the PNS of sea lamprey. On the other hand, NKX2.2, a gene required for oligodendrocyte differentiation in the CNS of jawed vertebrates is also expressed in the ventral ventricular zone, and later in the marginal layer of the lamprey neural tube. In the CNS of jawed vertebrates, Sox8 and Sox10 are specific to oligodendrocytes. Lamprey SoxE2 (Sox10) is also expressed in the CNS. A lamprey specific SoxE gene, SoxE1, is expressed at motor exit points along the trunk neural tube. To determine the function of SoxE genes and NKX2.2 in lamprey gliogenesis, Morpholino and CRISPR-Cas were used to eliminate SoxE and Nkx2.2 function. By analyzing the regulatory network of lamprey gliogenesis, we expect to determine the ancestral cell type of vertebrate myelinated glia that existed in early vertebrates.
