In vivo time-lapse imaging shows dynamic oligodendrocyte progenitor behavior during zebrafish development

Abstract

Myelinating oligodendrocytes arise from migratory and proliferative oligodendrocyte progenitor cells (OPCs). Complete myelination requires that oligodendrocytes be uniformly distributed and form numerous, periodically spaced membrane sheaths along the entire length of target axons. Mechanisms that determine spacing of oligodendrocytes and their myelinating processes are not known. Using in vivo time-lapse confocal microscopy, we show that zebrafish OPCs continuously extend and retract numerous filopodium-like processes as they migrate and settle into their final positions. Process remodeling and migration paths are highly variable and seem to be influenced by contact with neighboring OPCs. After laser ablation of oligodendrocyte-lineage cells, nearby OPCs divide more frequently, orient processes toward the ablated cells and migrate to fill the unoccupied space. Thus, process activity before axon wrapping might serve as a surveillance mechanism by which OPCs determine the presence or absence of nearby oligodendrocyte-lineage cells, facilitating uniform spacing of oligodendrocytes and complete myelination.

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

“…We next labeled sections of double transgenic embryos and larvae with an antibody specific to zebrafish Sox10 (Park et al, 2005), which is the earliest known marker for OPCs. From 48 hpf, at the onset of OPC migration, through 96 hpf, when OPCs wrap axons and differentiate into mature oligodendrocytes (Kirby et al, 2006), we found two classes of Sox10 + cells: nkx2.2a + olig2 + Sox10 + cells and nkx2.2a − olig2 + Sox10 + cells (Fig. 2C-E).…”

“…Whereas in chick OPCs appear to arise from Nkx2.2 + spinal cord precursors (Soula et al, 2001), mouse OPCs express Nkx2.2 only after they initiate migration from their ventral spinal cord origin (Qi et al, 2001;Zhou et al, 2001;Fu et al, 2002). Zebrafish express two nkx2.2 paralogs, nkx2.2a and nkx2.2b (Barth and Wilson, 1995;Schafer et al, 2005) and our previous work showed that at least some OPCs express an nkx2.2a transgene (Kirby et al, 2006). Furthermore, zebrafish Nkx2.2a has greater amino acid identity with mammalian Nkx2.2 than Nkx2.2b.…”

“…Zebrafish strains used in this study included AB,Tg(nkx2.2a:megfp) vu17 (Kirby et al, 2006;Kucenas et al, 2008), Tg(olig2:dsred2) vu19 (Kucenas et al, 2008) and Tg (sox10(7.2):mrfp) vu234 (Kucenas et al, 2008). Embryos were produced by pair-wise matings, raised at 28.5°C in egg water or embryo medium and staged according to hours postfertilization (hpf).…”

“…To investigate the relationship between gene expression and OPC formation more directly, we examined transverse sections of Tg(nkx2.2a:megfp);Tg(olig2:dsred2) embryos, which express membrane-tethered EGFP under control of nkx2.2a regulatory DNA (Kirby et al, 2006;Kucenas et al, 2008) and DsRed2 under control of olig2 (Kucenas et al, 2008), respectively. At 24 hpf, EGFP + and DsRed2 + spinal cord cells occupied distinct, but contiguous domains ( Fig.…”

“…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).…”