Characterization of basic proteins from goldfish myelin

A Tale of Two Citrullines—Structural and Functional Aspects of Myelin Basic Protein Deimination in Health and Disease

Myelin basic protein (MBP) binds to negatively charged lipids on the cytosolic surface of oligodendrocyte membranes and is responsible for adhesion of these surfaces in the multilayered myelin sheath. The pattern of extensive post-translational modifications of MBP is dynamic during normal central nervous system (CNS) development and during myelin degeneration in multiple sclerosis (MS), affecting its interactions with the myelin membranes and with other molecules. In particular, the degree of deimination (or citrullination) of MBP is correlated with the severity of MS, and may represent a primary defect that precedes neurodegeneration due to autoimmune attack. That the degree of MBP deimination is also high in early CNS development indicates that this modification plays major physiological roles in myelin assembly. In this review, we describe the structural and functional consequences of MBP deimination in healthy and diseased myelin.

Characterization of myelination in the developing zebrafish

Myelination, the process by which glial cells ensheath and electrically insulate axons, has been investigated intensely. Nevertheless, knowledge of how myelination is regulated or how myelinating cells communicate with neurons is still incomplete. As a prelude to genetic analyses of these processes, we have identified zebrafish orthologues of genes encoding major myelin proteins and have characterized myelination in the larval zebrafish. Expression of genes corresponding to proteolipid protein (PLP/DM20), myelin protein zero (P0), and myelin basic protein (MBP) is detected at 2 days postfertilization (dpf), first in the ventral hindbrain, close to the midline. During the next 8 days, expression spreads rostrally to the midbrain and optic nerve, and caudally to the spinal cord. DM20 is expressed in the CNS only, while MBP transcripts are detected both in the CNS and in Schwann cells of the lateral line, cranial nerves, and spinal motor nerves. Unlike its closest homologue, trout IP1, zebrafish P0 transcripts were restricted to the CNS. Ultrastructurally, the expression of myelin genes correlated well with myelination, although myelination showed a temporal lag. Myelinated axons were first detected at 4 dpf in the ventral hindbrain, where they were loosely wrapped by processes of glia cells. By 7 dpf, bundles of heavily myelinated axons were observed in the same region. Axons in the lateral line and optic nerves were also surrounded by compact myelin. Conservation in gene expression patterns and the early appearance of myelinated axons, support using the zebrafish to dissect the process of myelination by a genetic approach.