Abstract
Radial glial cells (RGCs) are the first cell populations of glial nature to appear during brain ontogeny. They act as primary progenitor (stem) cells as well as a scaffold for neuronal migration. The proliferative capacity of these cells, both in development and in adulthood, has been subject of interest during past decades. In contrast with mammals where RGCs are restricted to specific ventricular areas in the adult brain, RGCs are the predominant glial element in fishes. However, developmental studies on the RGCs of cartilaginous fishes are scant. We have studied the expression patterns of RGCs markers including glial fibrillary acidic protein (GFAP), brain lipid binding protein (BLBP), and glutamine synthase (GS) in the telencephalic hemispheres of catshark (Scyliorhinus canicula) from early embryos to post-hatch juveniles. GFAP, BLBP and GS are first detected, respectively, in early, intermediate and late embryos. Expression of these glial markers was observed in cells with radial glia morphology lining the telencephalic ventricles, as well as in their radial processes and endfeet at the pial surface and their expression continue in ependymal cells (or tanycytes) in early juveniles. In addition, BLBP- and GS-immunoreactive cells morphologically resembling oligodendrocytes were observed. In late embryos, most of the GFAP- and BLBP-positive RGCs also coexpress GS and show proliferative activity. Our results indicate the existence of different proliferating subpopulations of RGCs in the embryonic ventricular zone of catshark. Further investigations are needed to determine whether these proliferative RGCs could act as neurogenic and/or gliogenic precursors.
Highlights
The telencephalon is one of the most studied areas in the entire central nervous system (CNS) since it develops into various structures that are responsible of complex functions such as cognition, memory or development of social skills
We investigated the expression pattern of glial fibrillary acidic protein (GFAP), brain lipid binding protein (BLBP) and glutamine synthase (GS) in a series of catshark embryos representative of the early (S25–S26), middle (S27–S31) and late (S32–S34) periods of telencephalic development (Ballard et al 1993)
Our results indicate that the surface of the catshark telencephalic ventricles in later embryonic stages consists of subsets of radial glial cells (RGCs); double immunofluorescence against GFAP, BLBP and GS reveals the presence of subpopulations of RGCs in the ventricular surface
Summary
The telencephalon is one of the most studied areas in the entire central nervous system (CNS) since it develops into various structures that are responsible of complex functions such as cognition, memory or development of social skills. In the embryonic mouse forebrain, with the onset of neurogenesis (E9–E10), NECs present in the neural tube give rise to radial glial cells (RGCs), the first cell type of glial nature arising in the developing central nervous system (for review see: Götz and Huttner 2005; Alvarez-Buylla and Kriegstein 2013; Götz 2013; Turrero and Harwell 2017) These cells were first described in the nineteenth century in the embryonic spinal cord and cerebral cortex by Camillo Golgi and Giussepe Magini, respectively (for review see: Bentivoglio and Mazzarello 1999; Kriegstein and Götz 2003; Farkas and Huttner 2008; Götz 2013). RGCs act as progenitor cells in the developing telencephalon of non-mammalian vertebrate groups including reptiles (Clinton et al 2014; Martínez-Cerdeño et al 2016) amphibians (D’Amico et al.2011; Moreno and González 2017) and teleosts (Lyons et al 2003; Alexandre et al 2010)
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