Oligodendrocyte origin and development in the zebrafish visual system

Abstract

Oligodendrocytes are the myelinating cells in the central nervous system. In birds and mammals, the oligodendrocyte progenitor cells (OPCs) originate in the preoptic area (POA) of the hypothalamus. However, it remains unclear in other vertebrates such as fish. Thus, we have studied the early progression of OPCs during zebrafish visual morphogenesis from 2 days post fertilization (dpf) until 11 dpf using the olig2:EGFP transgenic line; and we have analyzed the differential expression of transcription factors involved in oligodendrocyte differentiation: Sox2 (using immunohistochemistry) and Sox10 (using the transgenic line sox10:tagRFP). The first OPCs (olig2:EGFP/Sox2) were found at 2 dpf in the POA. From 3 dpf onwards, these olig2:EGFP/Sox2 cells migrate to the optic chiasm, where they invade the optic nerve (ON), extending toward the retina. At 5 dpf, olig2:EGFP/Sox2 cells in the ON also colocalize with sox10:tagRFP. When olig2:EGFP cells differentiate and present more projections, they become positive only for sox10:tagRFP. olig2:EGFP/sox10: tagRFP cells ensheath the ON by 5 dpf when they also become positive for a myelin marker, based on the mbpa:tagRFPt transgenic line. We also found olig2:EGFP cells in other regions of the visual system. In the central retina at 2 dpf, they are positive for Sox2 but later become restricted to the proliferative germinal zone without this marker. In the ventricular areas of the optic tectum, olig2:EGFP cells present Sox2 but arborized ones sox10:tagRFP instead. Our data matches with other models, where OPCs are specified in the POA and migrate to the ON through the optic chiasm.

Zebrafish embryonically exposed to valproic acid present impaired retinal development and sleep behavior

“…(g-l) Staining for Sox2 transcription factor showed positive cells in the layered retina in embryos (g, h) larvae (i, j) and juveniles (k, l). Sox2 positive cells in the PGZ and in different layers of differentiated retina has been previous described(DeOliveira-Mello et al, 2019;Santos-Ledo et al, 2022) and was similar in VPA-exposed zebrafish and controls. (g, h) Cones showed a delay in embryos (2-dpf) exposed to VPA (white arrow; magnification in h').…”

“…We analyzed expression of developmental ( sox2, notch1a and neurod1 ), glial ( pax2a, sox10 and apoeb ), aminergic ( sertb and th1 ), and apoptosis related ( casp3a ) genes. The expression of these genes in the zebrafish retina and/or optic nerve has been previously reported (Chen et al, 2012; Hutchinson et al, 2012; Otis et al, 2015; Priyadarshini et al, 2013; Rauch et al, 2003; Santos‐Ledo et al, 2022; Wang et al, 2006). Notch1a, neurod1 , pax2a , sox10 , apoeb , sertb , and casp3a mRNA expression of VPA‐exposure zebrafish at 5‐dpf (Figure 4) was similar in VPA‐exposed and control larvae.…”

Age-related dysregulation of the retinal transcriptome in African turquoise killifish

“…The resident immune cells, marked by csf1r , lined the IPL (Figure 3L), as expected for resting microglia/macrophages (Murenu et al, 2022). Notably, in contrast to mammals, we identified oligodendrocytes ( plp1b, cldn19 ), highly abundant in the optic nerve head (Figure S5I) and sparsely distributed throughout the retina in the GCL (Figure 3M, Figure S5I) and the INL (Figure S5I, arrowhead) (Nakazawa et al, 1993; Santos-Ledo et al, 2023).…”

“…Single-cell transcriptomics were used to delineate the cellular landscape of the killifish retina. The killifish retina contains all major cell classes, as well as oligodendrocytes, previously reported to be present in fish and avian retinas (Nakazawa et al, 1993; Santos-Ledo et al, 2023). Additionally, age-related changes in gene expression across the cell types were determined by combining the single-cell with the bulk RNA-seq datasets.…”

Retinal ganglion cell topography and spatial resolving power in the pajama cardinalfish Sphaeramia nematoptera (Bleeker, 1856)

“…performs a variety of functions in the fish retina, including defense against various harmful agents, scavenging cell debris, and regulation of nerve tissue homeostasis, growth, and regeneration(Huang et al, 2012;Salvador-Silva et al, 2000). Oligodendroglia's main function is forming the myelin sheath around axons(Santos-Ledo et al, 2023).…”