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DNA synthesis and the incorporation of labeled iris cells into the lens during lens regeneration in adult newts

1971; Elsevier BV; Volume: 24; Issue: 4 Linguagem: Inglês

10.1016/0012-1606(71)90063-7

1095-564X

Randall W. Reyer,

Intraocular Surgery and Lenses

When the lens was removed from the eye of adultNotophthalmus viridescens and the specific DNA precursor, thymidine-3H, was injected intraperitoneally, the initiation of DNA synthesis was indicated by the appearance of labeled nuclei in the pigmented iris epithelium 4 days after lentectomy. As the cells near the mid-dorsal pupillary margin then undergo depigmentation to form a lens vesicle, DNA replication and mitotic cell division continue in this tissue. Cells which were labeled in the dorsal iris epithelium could be traced into all parts of the young, regenerating lens, including both the lens epithelium and the lens fibers. This radioautographic evidence, together with the histological evidence for continuity of the iris epithelium and the regenerating lens, provides support for the concept that dorsal iris cells transform into lens cells. As soon as the cells in the inner lamina of the lens vesicle begin to elongate to differentiate into primary lens fibers, DNA synthesis ceases in these cells but continues in the cells of the outer part of the lens vesicle and in the stalk connecting the lens vesicle with the rest of the iris epithelium. Cells in the latter areas continue to synthesize DNA and to divide, the daughter cells moving toward the primary lens fibers. In the equatorial zone, these cells begin to elongate, stop dividing and enclose the primary lens fibers with a shell of secondary lens fibers. As the lens grows in size, it detaches from the iris epithelium but the lens epithelium remains as a germinal epithelium providing a continuous supply of new secondary lens fibers. Although DNA synthesis is initiated in the iris epithelium by 7 days after extirpation of both lens and neural retina, the other phases of lens regeneration are delayed until a layer of depigmented cells has been formed by the regenerating neural retina. Unlabeled iris and lens vesicles were implanted into lentectomized eyes at different times after administration of thymidine-3H to the host in order to test for the availability time of the isotope. Conspicuous labeling of the implant nuclei occurred up to two hours after injection and then dropped off so that no label was found from 3.5 hours to 14 days after injection. There was one exception where a light label appeared in a lens vesicle exposed to the host eye environment 2–3 days after isotope injection. It was concluded that the thymidine-3H is available for only 2–3 hours in most instances.