Open AccessDIURNAL VARIATION IN THE LABELING INDEX OF MOUSE EPIDERMIS: A DOUBLE ISOTOPE AUTORADIOGRAPHIC DEMONSTRATION OF CHANGING FLOW RATES
Author(s) -
Crube D. D.,
Auerbach H.,
Brues A. M.
Publication year - 1970
Publication title -
cell proliferation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.647
H-Index - 74
eISSN - 1365-2184
pISSN - 0960-7722
DOI - 10.1111/j.1365-2184.1970.tb00344.x
Subject(s) - thymidine , hairless , chemistry , efflux , dna synthesis , tritium , diurnal temperature variation , isotope , colcemid , period (music) , biochemistry , microbiology and biotechnology , biology , dna , cell , physics , atmospheric sciences , quantum mechanics , nuclear physics , geology , acoustics
A diurnal rhythmicity in the labeling index was observed in the epidermis of hairless mice, injected with either 14 C‐ or 3 H‐thymidine, at different times during a 24 hr period. A modified autoradiographic technique, using 14 C‐ and 3 H‐thymidine and two overlying emulsion layers, makes it possible to clearly differentiate synthesizing cells which are singly labeled with either carbon‐14 or tritium, and cells labeled with both isotopes. At various times during a 24 hr period, hairless mice were injected with thymidine‐2‐ 14 C and colcemid, followed at 2 or 3 hr by a second injection of 3 H‐thymidine. The labeling indices were calculated for the 14 C‐ and 3 H‐thymidine injection times. These labeling indices were consistent with the control, single isotope, labeling indices and exhibited the same diurnal rhythm. Cells singly labeled with 3 H‐ or 14 C‐thymidine have either started or completed DNA synthesis during the interval between the two injections. Flow rates into and out of DNA synthesis, throughout the 24 hr period, can be calculated from these singly labeled cells. The flow rates varied rhythmically throughout the day and paralleled changes in the labeling indices. The influx and efflux flow rates, at all times measured, were not equal. The influx flow rate was reflected in the efflux rate at a time later equal to the duration of S. By means of these flow rates, the per cent of cells in DNA synthesis was calculated for each hour during a 24 hr period. The resulting labeling index curve matches the observed 24 hr diurnal rhythm in labeling indices. By extension of these flow rates through mitosis, the resulting mitotic index curve is comparable to the reported 24 hr diurnal rhythm in mitotic indices.