[Effect of actinomycin D on the formation of the photoreceptor ultrastructure of the retina in the chick embryo].

The influence of actinomycin D on the ultrastructure of retina photoreceptors in 10, 11 and 12 day old chick embryos was studied. Actinomycin D was shown to provoke certain changes in the ultrastructure of differentiating retina visual cells as soon as 1 hour after injection. These changes involve segregation and diffusion of nucleoli, changes in mitochondrial matrix, destruction of their external membranes and cristae, changes in the diameter and length of canals of endoplasmic reticulum, disintegration of polysomes. The noted changes do not prevent a further differentiation of the internal segments - ellipsoid and paraboloid of visual cells, but considerably affect parametres of these organelles. The formation of membrane disks of photoreceptors is inhibited after a 24 hours incubation with the inhibitor, when actinomycin D was injected to 11 day old embryos. Injection of actinomycin D into 12 day old chick embryos, after a 24 hours incubation with the inhibitor, does not inhibit a formation of membrane disks of photoreceptors, but somewhat retards their differentiation. This effect may be associated with the transcription o mRNA for protein synthesis of the membrane disks, which presumably takes place on the 11th day of the chick embryo incubation.