The distribution of intercellular gap junctions in the developing retina and pigment epithelium of Xenopus laevis

Calcium binding in pigmented and albino eyes

The localization of calcium binding sites in eyes was determined autoradiographically after extracting endogenous Ca from tissue sections and replacing it with 45Ca. The strongest labeling was associated with pigmented tissues due to the high concentration of melanin, which was shown to bind Ca effectively and in a pH-dependent fashion. The second strongest binding was over the tapetum lucidum of the cat eye, and moderate labeling was associated with eye muscles and epithelium and endothelium of the cornea. The neural retina was generally more lightly labeled than the surrounding tissue of the eye; here the plexiform layers stood out in comparison to the nuclear layers, as did a band located internal to the photoreceptor outer segments. The possibility that the Ca buffering capacity of melanin may represent the common denominator for the various neurological defects found in hypopigmentation mutants is discussed.

Effects of colchicine on gap junction formation during retinal neurogenesis

Colchicine, injected into the amniotic cavity of 3 to 10 day-old chick embryos, has the following effects on the developing retina: 1. Cells in arrested metaphase accumulate in the ventricular portion of the matrix region. If colchicine is applied at the end of the first week of incubation, the kinetic migration of the cell nuclei is inhibited. 2. The cells lose their typical slender, bipolar shape to become ovoid to spherical. These morphological changes are more obvious when colchicine acts during the first week of incubation. 3. The formation of temporary gap junctions between the matrix cells of the retina occurs during the first week of development. When colchicine is administered around the 3rd day of incubation, the assembly of intramembranous particles (IMPs) during gap junctions formation is incomplete. These results suggest that an intact microtubular system within the submembranous cytoskeleton is essential for the assembly of these intercellular contacts.