Isl1 and CERN-922 immunoreactivities progressed in parallel following a central-to-peripheral gradient, but Isl1 immunoreactivity extended to more peripheral regions (Figures 5(d)�C5(g)).Figure 5Morphological features and expression patterns of Isl1 and other cell differentiation markers in the St37/38 Xenopus laevis retina. (a) Toluidine blue-stained transverse both retinal resin sections showed that the plexiform layers were observed across the …At St40, the typical multilayered structure of the retina was clearly distinguishable. However, the GCL was many cells thick, and the plexiform layers were poorly developed (Figure 6(a)). A proliferative population of undifferentiated cells remained at the ciliary margin zone (CMZ), providing a source of new cells for the growing retina (Figure 6(a)).
At this stage, the expression patterns for Isl1 (Figures 6(b), 6(e), and 6(f)), SV2 (Figure 6(c)), and CERN-922 (Figures 6(d) and 6(f)) followed a central-to-peripheral gradient. The number of Isl1 immunoreactive elements and the immunostaining intensity increased markedly in the INL and began to resemble those observed in the St53 retina (Figure 2). The patterns of distribution of Isl1 positive cells during X. laevis retinal development are summarized in Figure 7.Figure 6Morphological features and expression patterns of Isl1 and other cell differentiation markers in the St40 Xenopus laevis retina. (a) Toluidine blue-stained transverse retinal resin sections revealed that the typical multilayered structure was clearly …Figure 7Schematic drawings of the Isl1 positive cells in the developing retina of Xenopus laevis.
Black nuclei represent Isl1-immunostained cells. (a) Isl1 immunoreactivity during St29�C31 was restricted to nuclei located near the vitreal surface of the …4. DiscussionRecent studies conducted in our laboratory confirmed the presence of the LIM-domain transcription factor Isl1 in differentiating and mature ganglion, amacrine, bipolar, and horizontal cells in the retina of mammals , birds , reptiles , and fish [9�C11]. In the present study, we extend our observations to the retina of the anuran Xenopus laevis, an amphibian model extensively used in studies of retinal cell organization [44, 55�C57]. We first established the precise cell types that showed immunoreactivity for Isl1 in the differentiated retina, and subsequently analyzed the Isl1 immunoreactivity in the corresponding cells in the retina throughout development.
The Isl1 spatiotemporal expression pattern spans the differentiation of four neuronal classes��ganglion, amacrine, bipolar, and horizontal cells��in the developing X. laevis retina.4.1. Isl1 Expression in the Nonlayered Retina of X. laevis Dacomitinib Between St29 and 30, the first detectable Isl1 expression, and St 35-36, the plexiform layers were not recognizable in the developing X.