Cell cycle time and life-span of cells in the mouse eye. Measurements during the postfetal period using repeated 3H-thymidine injections.

In this investigation the cell cycle time and the life-span of cells in different tissues of the mouse eye were determined during postfetal development not with single but, instead, by means of repeated 3H-thymidine injections. The potential of this method applied for the first time in the mammalian eye, is thoroughly discussed. Essentially, four groups of 19-21 mice each, aged 1, 10, 20, and 60 days at the start of the experiment, received intraperitoneal injections of 3H-thymidine at a dose of 1 microCi/g body weight every 4 h for a maximum of 14 days, i.e. a total of up to 85 injections. Further animals were sacrificed after the 13th, 19th, 25th, 31st, 37th, 49th, 61st, 73rd, and 85th injections, i.e. 2, 3, 4, 5, 6, 8, 10, 12, and 14 days after the start of the experiment. When all the injections had been given, animals from each group were sacrificed on the 1st, 4th, 8th, 16th, and sometimes the 32rd, 48th, and 64th days, respectively, after the last injection. With this experimental paradigm it was possible: (1) to determine the cell cycle time and the life-span of the cells during postfetal development up to maturity without gaps; (2) to establish the end of the development by means of cell proliferation in various tissues of the mouse eye; herewith it was possible to determine the times at which the development by cell proliferation is replaced by development by cell differentiation, and (3) to clearly prove in which mature ocular tissues cell turnover still exists and in which it does not; this appears to be especially important, since in recent years the importance of cell proliferation process following injury and stimulation was also recognized in the eye, for example, in massive periretinal proliferation in connection with retinal detachment and retinal surgery, as well as in endothelial injuries following intraocular lens implantation; only when normal conditions are known can pathological proliferative processes be recognized as such and be distinguished from normal ones. The results are cumulatively represented in tabular form, from which details are to be extracted. As expected, cell cycle times are very short and seemingly homogeneous in tissues which develop within themselves, but become longer and inhomogeneous, except in the inner and outer granular layer of the retina, in which the cell proliferation comes to a particularly abrupt end. The shortest cell cycle time occurred in the cells of the vascular walls of the retina at the time of birth and was 24 h.(ABSTRACT TRUNCATED AT 400 WORDS)

[Mitotic activity of the pigment epithelium during embryonic and postembryonic development]. / Die mitotische Aktivität des Pigmentepithels während der embryonalen und postembryonalen Entwicklung. Untersuchungen mit Colchizin und 3H-Thymidin an Kaninchen, Ratten und Mäusen.

The purpose of the present study was to examine the mitotic activity of the normal pigment epithelium of the retina (RPE), the ciliary body and the iris of different animals during gestation and after birth by blocking the metaphase with colchicine and by marking the pigment epithelial nuclei with tritium-labeled thymidine. The colchicine examinations were made on 54 albino rabbits and 56 albino rats, the 3H-thymidine studies with 78 albino mice. In the rabbit the peak of mitotic activity (respectively the end) is found in the RPE at the beginning of the 2nd third of gestation (respectively at the 9th postnatal day), but in the pigment epithelium of the ciliary body and in the iris during the last third of gestation (respectively in the 2nd month of life and the 3rd postnatal week). In the rat the highest mitotic activity is reached in the RPE at the beginning of the 2nd half of gestation (respectively at the 13th postnatal day), in the ciliary body at the 3rd day of life (respectively the 24th postnatal day) and in the iris at the end of the gestational period (respectively the 17th postnatal day). In the mouse the highest rates of mitotic activity are found in the RPE from the 16th gestational day to the 8th day of life (respectively the 20th day of life), in the ciliary body from the 1st to the 4th day of life (respectively from the 12th to the 20th postnatal day) and in the iris on the 9th day of life (respectively the 12th to the 20th postnatal day). The present observations have also demonstrated that with maturation of all areas of the pigment epithelium, the mitotic activity stops. The cells of the pigment epithelium do not have an epithelial cell turnover but they are reversible postmitotic cells. Despite the enormous proliferative properties the pigment epithelium shows no regeneration by mitosis after severe damage.