Mitotic Variations in the Lens Epithelium of the Frog

Abstract

When frogs were exposed to cold temperature (4°C) the number of mitotic figures in the lens epithelium was reduced by 80–100%. However, mitotic activity does not vary directly with temperature. It is likely that other factors, such as hormones, also regulate proliferation in the germinative zone. Light-dark influences and diurnal changes have, on the other hand, not been observed to produce obvious effects. Implants of pituitary glands or lyophilized pituitaries stimulate cell division as do LH, TSH, T₃ and T₄. No steroids have yet been found effective in this regard. Somatotrophin and adrenaline are likewise ineffective. The stimulation by LH is not the result of a nonspecific immunological response, for bovine serum albumin injections exerted no detectable influence upon proliferation in the lens. When animals were transferred from 4 to 24 °C the MI increased substantially. This increase occurred on the first day of the transfer in summer frogs but took 8 days in winter frogs. Radioimmunoassay demonstrated a correlation between the number of mitosis and LH. In the transfer studies no correlation was found between serum concentrations of FSH, T₃ or T₄ and mitotic activity. A thermoendocrine hypothesis was presented to help explain the results obtained to date as well as to aid in the formulation of suitable experiments.

Unscheduled Dna Synthesis in Frog Lens at 5°c

“…Thus, unscheduled DNA labeling occurs in the frog even at very low temperatures. Since cold normally depresses mitotic activity in such animals (Rothstein and Worgul, 1973), it is unlikely that the diffuse labeling observed following UV irradiation was due to stimulation of replicative synthesis, particularly since virtually all cells were labeled. We conclude, tentatively, that the UV induced labeling observed in these cold incubated lenses represents repair synthesis of DNA.…”

“…Bullfrogs were maintained for 48 h in a cold room at 5°C in order to suppress their mitotic activity (Rothstein and Worgul, 1973). Following this they were decapitated and the lenses removed and placed epithelial cell side up in ice cold phosphate buffer.…”