At these stages, Isl1 expression was detected in MEK162 clinical trial abundant newly formed postmitotic cells that accumulated in the vitreal surface of the central and mid-peripheral undifferentiated retina and in sparse migrating neuroblasts in outer regions of the NbL (Figure 4(b)). We compared the Isl1 expression pattern with that of other cell differentiation markers. Thus, we used an antibody against the transmembrane synaptic vesicle glycoprotein SV2 that has been demonstrated to be a powerful tool to label the first optic axons emerging from young ganglion cells [10, 11, 46] and also to address the appearance of functional synapses [10, 11, 46�C49]. Thus, strong SV2-immunoreactive ganglion cell axons were detected in the presumptive optic fibre layer (OFL), coursing to the optic nerve exit (Figure 4(c)).

Surprisingly, strong SV2 immunoreactivity was also found in the scleralmost part of the neuroepithelium, suggesting that differentiating cells were also located in this region (Figure 4(c)). Therefore, we used a polyclonal antibody against bovine rod opsin (CERN-922) that has been described as an excellent photoreceptor marker in fish [9�C11, 50�C53], reptiles (unpublished observations), birds (unpublished observations), and mammals [54]. A similar antibody has been previously used to identify rod photoreceptors in the developing X. laevis retina [45]. Sparse morphologically immature CERN-922-immunoreactive photoreceptors were detected in the central region of the retina (Figures 4(d)�C4(f)). Therefore, in discordance with the undifferentiated morphological appearance of the X.

laevis retina, several differentiating cell populations could be observed by these stages.Figure 3Morphological features and expression patterns of Isl1 in the St29/30 ((a), (b)) and St31 ((c), that Isl1 is also expressed by undi (d)) Xenopus laevis retina. ((a), (c)) Toluidine blue-stained transverse retinal resin sections showed that the neural …Figure 4Morphological features and expression patterns of Isl1 and other cell differentiation markers in the St35/36 Xenopus laevis retina. (a) Toluidine blue-stained transverse retinal resin sections showed that neural retina remained undifferentiated during …At St 37/38, the inner plexiform layer (IPL) was formed above the GCL, which was several cells thick, along the middle third of the retina (Figures 5(a), 5(d), and 5(g)).

Furthermore, at this stage also, the first sign of the OPL could be observed, separating the outer nuclear layer (ONL) from the INL (Figures 5(a), 5(d), and 5(g)). SV2 antibody also revealed the emergence of the plexiform layers in the central and the mid-peripheral retina (Figure Anacetrapib 5(b)). By this stage, most Isl1-immunoreactive cells were confined to the newly formed GCL (Figure 5(c)). However, many Isl1-positive cells appeared at this stage in the INL.