Neuronal and glial differentiation during lizard (Gallotia galloti) visual system ontogeny

Abstract

We studied the histogenesis of the lizard visual system (E30 to adulthood) by using a selection of immunohistochemical markers that had proved relevant for other vertebrates. By E30, the Pax6(+) pseudostratified retinal epithelium shows few newborn retinal ganglion cells (RGCs) in the centrodorsal region expressing neuron- and synaptic-specific markers such as betaIII-tubulin (Tuj1), synaptic vesicle protein-2 (SV2), and vesicular glutamate transporter-1 (VGLUT1). Concurrently, pioneer RGC axons run among the Pax2(+) astroglia in the optic nerve and reach the superficial optic tectum. Between E30 and E35, the optic chiasm and optic tract remain acellular, but the latter contains radial processes with subpial endfeet expressing vimentin (Vim). From E35, neuron- and synaptic-specific stainings spread in the retina and optic tectum, whereas retinal Pax6, and Tuj1/SV2 in RGC axons decrease. Müller glia and abundant optic nerve glia express a variety of glia-specific markers until adulthood. Subpopulations of optic nerve glia are also VGLUT1(+) and cluster differentiation-44 (CD44)-positive but cytokeratin-negative, unlike the case in other regeneration-competent species. Specifically, coexpression of CD44/Vim and glutamine synthetase (GS)/VGLUT1 reflects glial specialization, insofar as most CD44(+) glia are GS(-). In the adult optic tract and tectum, radial glia and free astroglia coexist. The latter show different immunocharacterization (Pax2(-)/CD44(-) /Vim(-)) compared with that in the optic nerve. We conclude that upregulation of Tuj1 and SV2 is required for axonal outgrowth and search for appropriate targets, whereas Pax2(+) optic nerve astroglia and Vim(+) radial glia may aid in early axonal guidance. Spontaneous axonal regrowth seems to succeed despite the heterogeneous mammalian-like glial environment in the lizard optic nerve.

A comparative analysis of Müller glia-mediated regeneration in the vertebrate retina

“…The expression levels of Pax2 are increased by acute retinal damage or treatment with insulin and FGF2 (Stanke et al 2010). In addition, Pax2 is expressed by most Müller glia in central regions of the lizard retina (Romero-Aleman et al 2012), and some of the Müller glia in central regions of the zebrafish retina (Boije et al 2010). Pax2 is not expressed by Müller glia in the mammalian retina (Stanke et al 2010).…”

Comparative analysis of glucagonergic cells, glia, and the circumferential marginal zone in the reptilian retina

“…The regenerative capacity of Müller glia is remarkably robust in zebrafish while it is reduced in chicken and mammalian retina. There are few studies describing the characteristics of retinal glia in reptiles (Casanas et al, 2011; Dahl et al, 1985; Gaur et al, 1988; Romero-Aleman et al, 2012; Romero-Aleman et al, 2010). Therefore, another purpose of this study is to characterize the glial cells in the retinas of lizards, snakes, and turtles.…”

Nogo‐A does not inhibit retinal axon regeneration in the lizard Gallotia galloti

“…In the immunoblots, Tuj1 recognizes a single protein band of an apparent molecular weight of ∼47 kDa in G. galloti brain extracts (Romero‐Alemán et al, ). Tuj1 showed a neuron‐specific labeling in the developing and regenerating lizard CNS (Romero‐Alemán et al, ).…”