Development and DNA synthesis in the retina of chick embryo observed by light and electron microscopic radioautography.

The incorporation of 3H-thymidine into DNA was examined in the chick embryo retina in early development during the period of the optic vesicle formation (day 2) before the formation of the basic layers of retina (day 7) by means of light and electron microscopic radioautography. Labeling index with 3H-thymidine reached the maximum on day 2 and declined thereafter. The patterns of localization of labelled cells and average grain counts were compared in the anterior, equatorial and posterior regions of the retina. On day 2, more labelled cells were found in the posterior region than the other two regions of the retina. Most of the labelled cells were found in the outer portion of the retinal layer throughout the retina. On day 3, most labelled cells were found in the anterior region and decreased in the posterior one. On day 4, labelled cells dominated in the anterior and equatorial regions. In these two regions, more labelled cells were present in the outer portion of the retinal layer, while in the posterior region these cells were seen in the inner portion of the retinal layer.