A genetic screen identifies genes essential for development of myelinated axons in zebrafish

Abstract

The myelin sheath insulates axons in the vertebrate nervous system, allowing rapid propagation of action potentials via saltatory conduction. Specialized glial cells, termed Schwann cells in the PNS and oligodendrocytes in the CNS, wrap axons to form myelin, a compacted, multilayered sheath comprising specific proteins and lipids. Disruption of myelinated axons causes human diseases, including multiple sclerosis and Charcot-Marie-Tooth peripheral neuropathies. Despite the progress in identifying human disease genes and other mutations disrupting glial development and myelination, many important unanswered questions remain about the mechanisms that coordinate the development of myelinated axons. To address these questions, we began a genetic dissection of myelination in zebrafish. Here we report a genetic screen that identified 13 mutations, which define 10 genes, disrupting the development of myelinated axons. We present the initial characterization of seven of these mutations, defining six different genes, along with additional characterization of mutations that we have described previously. The different mutations affect the PNS, the CNS, or both, and phenotypic analyses indicate that the genes affect a wide range of steps in glial development, from fate specification through terminal differentiation. The analysis of these mutations will advance our understanding of myelination, and the mutants will serve as models of human diseases of myelin.

KBP is essential for axonal structure, outgrowth and maintenance in zebrafish, providing insight into the cellular basis of Goldberg-Shprintzen syndrome

“…The kbp st23 mutation was identified in an ENU-based screen for mutations that disrupted myelinated axons (Pogoda et al, 2006). Tg(Foxd3:gfp) 17 fish (Gilmour et al, 2002) were kindly provided by Darren Gilmour, and Tg(HuC:kaede) rw0130a fish (Sato et al, 2006) by Hitoshi Okamoto.…”

“…All of these steps were accelerated by a microwave stimulation regime using the PELCO 3470 Multirange Laboratory Microwave System (Pelco) and kept at 15°C in a cooled water bath using the PELCO Steady Temp throughout. Following dehydration, embryos were embedded in Epon, and stained and imaged as described previously (Pogoda et al, 2006).…”

“…In a screen for zebrafish mutants with abnormalities in myelinated axons, we uncovered a mutation, kbp st23 , in a gene that is required for the development of peripheral axons in the larva (Pogoda et al, 2006). Analyses using the transgene Tg(HuC:kaede) (Sato et al, 2006) showed that by 28 hpf, migrating growth cones of wild-type animals have reached somite 11-12 (Fig.…”

How to make a teleost adenohypophysis: Molecular pathways of pituitary development in zebrafish

“…Since then, many additional screens using more specific or sophisticated screening assays greatly contributed to today's collection of available mutants (e.g. (Muto et al, 2005, Pogoda et al, 2006a, Sun et al, 2004). At the same time, genomic tools have enormously improved, facilitating the cloning of randomly induced mutations (Dahm and Geisler, 2006, Sivasubbu et al, 2007.…”

nkx2.2apromotes specification and differentiation of a myelinating subset of oligodendrocyte lineage cells in zebrafish

“…Numerous studies have addressed the genetic mechanisms that direct development of zebrafish primary neurons (Lewis and Eisen, 2003). More recently, zebrafish have begun to be used as a model for investigation of myelination (Brosamle and Halpern, 2002;Kirby et al, 2006;Pogoda et al, 2006).…”