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

Abstract

Retinal progenitors in the circumferential margin zone (CMZ) and Müller glia-derived progenitors have been well-described in the eyes of fish, amphibians and birds. However, there is no information regarding a CMZ and the nature of retinal glia in species phylogenetically bridging amphibians and birds. Thus, the purpose of this study was to examine the retinal glia and investigate whether a CMZ is present in the eyes of reptilian species. We used immuno-histochemical analyses to study retinal glia, neurons that could influence CMZ-progenitors, the retinal margin, and non-pigmented epithelium (NPE) of ciliary body of garter snakes, queen snakes, anole lizards, snapping turtles, and painted turtles. We compare our observations in reptile eyes to the CMZ and glia of fish, amphibians and birds. In all species, Sox9, Pax6 and the glucocorticoid receptor are expressed by Müller glia and cells at the retinal margin. However, proliferating cells were found only in the CMZ of turtles, but not in the eyes of anoles and snakes. Similar to eyes of chickens, the retinal margin in turtles contains accumulations of GLP1/glucagonergic neurites. We find that filamentous proteins, vimentin and GFAP, are expressed by Müller glia, but have different patterns of sub-cellular localization in the different species of reptiles. We provide evidence that the reptile retina may contain Non-astrocytic Inner Retinal Glial (NIRG) cells, similar to those described in the avian retina. We conclude that the retinal glia, glucagonergic neurons and CMZ of turtles appears to be the most similar to that of fish, amphibians and birds.

Variations in the proliferative activity of the peripheral retina correlate with postnatal ocular growth in squamate reptiles

“…Squamate reptiles, similar to fish and amphibians, grow throughout their lifespan and thus represent another important model to study postembryonic neurogenesis. Previous studies, however, have so far failed to identify proliferating CMZ or RM progenitors in the few tested adult squamates (Beazley et al, ; Casañas et al, ; Dunlop et al, ; Todd et al, ). We first assessed the presence of a proliferating peripheral retina in a larger and more representative panel of lizards and snakes, including 24 different species covering all major groups of squamates (Figure a): Gekkota ( n = 4), Scincoidea ( n = 3), Lacertoidea ( n = 1), Anguimorpha ( n = 1), Iguania ( n = 10), and Serpentes ( n = 5).…”

“…The general consensus arising from these studies is a progressive reduction of the CMZ over the course of vertebrate evolution from fish to mammals (Kubota et al, ). However, one of the most specious groups of terrestrial vertebrates—squamate reptiles—has remained largely unexplored except for a recent comparative study investigating a few individuals from three different species (Todd et al, ). Here, we demonstrate for the first time that both lizards and snakes contain a source of postnatal proliferating progenitors in a newly identified pseudostratified RCJ region between the retina and the CB.…”

“…However, little is yet known about retinogenesis and morphogenesis of retinal tissues in the squamate group of reptiles (i.e., lizards and snakes), which occupies a key phylogenetic position within amniotes. In particular, whereas the precise anatomy of the reptilian eye has been well described over the past decades, only one recent study directly compared the activity of the peripheral retina in squamates, by using a limited taxon sampling (two snakes and one lizard) at an uncertain adult stage (Todd et al, ). Interestingly, the absence of proliferating CMZ or RM progenitors in squamates reported in the latter study is in line with older scattered studies focusing on optic nerve regeneration in several adult lizard species (Beazley, Tennant, Stewart, & Anstee, ; Casañas et al, ; Dunlop et al, ).…”

BMP‐ and TGFβ‐signaling regulate the formation of Müller glia‐derived progenitor cells in the avian retina

“…The identity of BrdU‐labeled cells was determined based on previous findings that 100% of the proliferating cells in the chick retina are comprised of Sox2/9 + Müller glia in the INL/ONL, Sox2/9/Nkx2.2 + Non‐Astrocytic Inner Retinal Glia (NIRG) cells in the IPL, GCL, and NFL (the NIRG cells do not migrate distally into the retina), and CD45 + (Sox2/9 – ) microglia (Fischer, Scott, Zelinka, & Sherwood, ; Zelinka, Scott, Volkov, & Fischer, ). NIRG cells are a unique type of glial cell that has been described in the chick retina (Fischer et al, ; Rompani and Cepko, ), and possibly the retinas of reptiles (Todd et al, ), that migrate into the retina from the optic nerve (Rompani and Cepko, ). Sox2 + nuclei in the INL were identified as Müller glia based on their large size and fusiform shape, which was distinctly different from the Sox2 + nuclei of cholinergic amacrine cells, which are small and round (Fischer et al, ).…”

Heparin-binding EGF-like growth factor (HB-EGF) stimulates the proliferation of Müller glia-derived progenitor cells in avian and murine retinas

“…Non-astrocytic Inner Retinal Glial (NIRG) cells are a distinct type of glial cell found in the inner layers of chick retinas (Fischer et al 2010) and possibly the retinas of reptiles (Todd et al 2015). Sox2 + nuclei in the INL were identified as Müller glia based on their large size and fusiform shape which are distinctly different from the Sox2+ nuclei of cholinergic amacrine cells which are small and round (Fischer et al 2010).…”