Activation of DNA replication in the iris epithelium by lens removal

Abstract

The pattern of DNA replication during the initial stages of Wolffian lens regeneration has been examined by an autoradiographic study of tritiated thymidine uptake in zero to five-day regenerates (Triturus viridescens). Scanning of complete sets of serial sections for each iris revealed the absence of labeled cells in normal, one-, and two-day iris epithelia, and a very infrequent occurrence of labeled iris epithelial cells in some three-day regenerates. After this stage, cell labeling is seen in all iris epithelia. Cell labeling frequency increases markedly by four days, and is at a very high level in five-day regenerates.Further data indicate that labeling begins in the dorsal sector of the iris epithelium.By five days after lens removal, however, it reaches siinilar levels in dorsal, lateral, and ventral sectors. Thus, DNA replication is induced throughout the iris epithelium after lens removal, even though the lateral and ventral sectors of the iris epithelium do not participate in actual lens formation.Comparison between the outer and inner laminae of the iris epithelium shows that during all stages studied the great majority of labeled cells are in the inner lamina.Earlier autoradiographic studies of generation and are not sufficient for anWolffian lens regeneration demonstrated swering these specific questions. The that the cells of adult newt iris epithelium autoradiographic study reported and disare activated to replicate DNA soon after cussed here was undertaken in hopes of lens removal, and maintain the activated providing such answers. condition until they start fiber differentiation (unpublished work of R. W. Rever. '64) indicate that another prominent cellular change at the initial stages of regeneration is the activation of ribosomal RNA synthesis. The relationship between induced ribosomal RNA synthesis and induced DNA replication has become an important issue in understanding the control mechanism of this system. For elucidating this issue we need to know whether or not DNA replication is completely repressed in the normal adult iris epithelium, and how long after lens removal the normal condition is maintained before DNA replication begins. We must also know the distribution pattern of the DNA-replicating cells within the iris epithelium in the early stages of regeneration. The autoradiographic studies cited above were focused on the overall pattern of DNA replication during the whole course of re- J. EXP. ZOOL., 171: 425-432Lens removal Lentectomy, either unilateral or bilateral, was performed on 35 adult newts, Triturus viridescens, by the method of Eisenberg and Yamada ('66). In the unilateral lentectomy, the left lens was routinely removed. The right unoperated ins could then serve as a contralateral control. A few entirely normal animals were also included in the experiment.Injection of labeled precursor Regeneration was allowed to proceed for one, two, three, four or five days. At each of these times, some animals were anaesthetized with tricaine (Sigma) and injected intraperiton...

Simultaneous demonstration of lens regeneration from dorsal iris and tumour production from ventral iris in the same newt eye after carcinogen administration

“…It is known that normal iris epithelium of the newt lacks cell replicative ability, but this begins on day 4 after lentectomy [21][22][23][24]. The percentages of the number of labeled cells and mitotic cells per iris epithelium increase from day 4 to 7.…”

In vivo study of lens regeneration in Rana cyanophlyctis under influence of vitamin A and ascorbic acid

“…However, recently it has been observed that the capability of retinal iris PECs to transdifferentiate into lens is not restricted to urodeles amphibians only but is widely conserved in almost all vertebrates (Okada, 2000;Jangir et al, 2000Jangir et al, , 2001Jangir et al, , 2005Acharya et al, 2003;Shekhawat et al, 2001). It is well studied that lentectomy stimulates the iris epithelial cells of the newt's eye to undergo DNA synthesis and proliferate (Eisenberg and Yamada, 1966;Yamada and Roesel, 1969;Reyer, 1971). Concomitantly, with these processes, melanosomes disappear from the pigmented epithelial cells of iris and thus undergo dedifferentiation.…”

Macrophage mobilization and morphology during lens regeneration from the iris epithelium in newts: Studies with correlated scanning and transmission electron microscopy

“…Following intraperitoneal injection of 3H-thymidine into Notophthalmus (Triturus) viridescens, Yamada and Roesel (1969) and Reyer (1971) observed a n occasional cell with labeled nucleus in the iris stroma of normal eyes, or of eyes in animals which were injected 1 or 2 days after lens removal before DNA synthesis is initiated in the iris epithelium. These labeled cells were believed to be connective tissue fibroblasts or macrophages.…”