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Biomedical subjects

C S Potten

Publications and source records attributed to C S Potten.

At least 235 records · Page 13Linked to original sources
PubMed1983

Cell cycle kinetics of cultured human epidermal keratinocytes.

When stratified epithelia maintained in culture are used for autoradiographic studies of labeling index, the emulsion is usually placed over the uppermost strata of the culture. In many cases the distance from the basal cell nucleus to the emulsion exceeds the average pathlength of beta-particle emissions from 14C or 3H. We describe a technique for inverting the cultures so that the emulsion can be brought into close association with the basal cells. Attempts to label cultured human epidermal keratinocytes using a pulse of [3H]- or [14C]-thymidine produced labeling only at the periphery of the colonies. This was noted when emulsion was laid on top of the colonies but also when the emulsion was in close contact with the "basal cells" adhering to the plastic culture vessel. Continuous labeling of the cultures produced nearly 100% labeling of all the basal layer, i.e., central and peripheral, indicating that the central cells were also in rapid cell cycle. The results are interpreted as indicating the presence of an efficient barrier to free diffusion over the center of the colonies, presumably due to the presence of several layers of corneocytes. Percent labeled mitoses (PLM) studies produced an unusual PLM curve with a well-defined third peak which showed a higher PLM than the second peak. These results may indicate that the cultures contain discrete cell populations with different cell kinetic phase durations.

Autoradiography↗
PubMed1983

The gastrointestinal syndrome and mucosal clonogenic cells: relationships between target cell sensitivities, LD50 and cell survival, and their modification by antibiotics.

The sensitivity of the target cells responsible for the gastrointestinal syndrome in mice was deduced from the steepness of the dose-survival curve for mice assessed on Day 7 after irradiation. The D0 value was 1.25 +/- 0.22 Gy, virtually identical to the value of 1.23 +/- 0.08 measured for microcolony-forming cells (clonogens) over about the same range of dose in concurrent experiments. The survival of clonogens was similar when assayed in mice surviving to Days 3, 4, or 5, but clonogenic sensitivity was lower when assessed on Day 7. This was shown at one dose to be due largely to a selection of mice with high colony counts with only a small contribution from crypt budding. The LD50 for mice corresponded to a surviving fraction of crypts of about 0.35. An injection of 5 mg streptomycin sulphate ip daily for 5 days after irradiation increased the latent period by about 1 day, increased the LD50 by about 1.4 Gy, but did not significantly change the survival of clonogens. These studies are the first to test and satisfy the interpretation of a dose-response curve for animal survival in terms of "target cell" survival, where measurements of both are made over a similar range of dose in concurrent experiments.

Animals↗
PubMed1982

Sensitivity of follicular melanoblasts in newborn mouse skin to tritiated thymidine: Evidence for a long term retention of label.

Injection of tritiated thymidine into newborn mice results in a progressive greying of hair that does not begin until after the first hair coat is grown. After a year the depigmentation is appreciable (about 60% of the hair are white). The effect cannot be simulated by external irradiation of newborn mice or by the administration of radioactive uridine or methionine. The effect can best be explained by a long-term retention of radioactivity in the DNA of melanocyte stem cells (melanoblasts) in spite of several rounds of cell division. This could be achieved by labelling the strands of DNA destined to act as templates throughout life by being selectively retained in the stem line as described in Cairns' hypothesis.

Animals↗
PubMed1982

Cell death (apoptosis) in the mouse small intestine after low doses: effects of dose-rate, 14.7 MeV neutrons, and 600 MeV (maximum energy) neutrons.

The production of dead (apoptotic) cells by low doses of gamma-rays was independent of dose-rate between 0.27 and 450 cGy per min. The r.b.e. for doses of 14.7 MeV neutrons between 1 and 15 cGy was about 4, and for neutrons generated by bombarding a beryllium target with 600 MeV protons the r.b.e. was about 2.7. The dose-incidence curves for all three radiation types reached a plateau at about 3-4 dead cells per crypt section, and this occurred at about 20-40 cGy of gamma-rays. These curves are compatible with exponential survival of the cell population at risk (D0 of 24 cGy for gamma-rays, 6 cGy for 14.7 MeV neutrons and 9 cGy for 600 MeV neutrons). Since the dose-response is exponential there is no indication of much higher r.b.e. values at very low doses, a point of concern in radiation protection. The spatial distribution of dead cells in the crypt was similar after doses of gamma-rays or neutrons, indicating that the same population of target cells was affected in both cases.

Animals↗
PubMed1982

Intestinal cell radiosensitivity: a comparison for cell death assayed by apoptosis or by a loss of clonogenicity.

Apoptotic and reproductive cell death have been assayed in the crypt of the small intestine. These two approaches result in survival curves with mean lethal doses (D0) that differ by a factor of 10. Widely differing doses and times of assay post-irradiation were used for the assays employing apoptosis in one case and clonogenicity in the other. The results obtained by the two approaches are compared. It is concluded that the cells that die via apoptosis represent a very sensitive subpopulation of the crypt (about 6 cells per crypt) that may or may not be clonogenic. Most clonogenic cells die at a later time by some other mechanism. If the apoptoses represent dead clonogenic cells they must be either a very sensitive subpopulation or, as deduced here, a subpopulation which is part of a uniformly resistant population of cells when clonogenicity is considered, but which is very sensitive to an early form of death.

Cell Survival↗
PubMed1982

A long-lived thymidine pool in epithelial stem cells.

The labelling index (LI) of the individual basal cell positions of the anterior column of mouse tongue filiform papillae was assessed with time after an injection of [3H]TdR at 12.00 hours (the minimum point in the circadian LI rhythm). An initial doubling of the LI in the stem cell zone due to cell division was followed by a second rise of 14-16% 16 hr after injection and this occurred even in the presence of vincristine. Although the uptake of [3H]TdR and the initial LI doubling were largely prevented by a preceding injection of hydroxyurea, the 14-16% LI rise was still observed. The possible explanations are discussed, the favoured one being that an average of one of the six or seven cells (the stem cell) in each stem cell zone can store [3H]TdR in a long-lived precursor pool for at least 16 hr before being utilized for DNA synthesis. This complements previously published work which suggested that one cell in each stem cell zone may selectively segregate DNA at mitosis.

Animals↗
PubMed1982

Evidence for discrete cell kinetic subpopulations in mouse epidermis based on mathematical analysis.

Continuous (repeated) labelling studies in mouse epidermis indicate that nearly all cells are labelled after about 100 hr. Percentage labelled mitoses studies ([3H]TdR at 15.00 and 03.00 hours) have a first peak that does not reach 100% and has a half-width of about 10 hr. Small second and third peaks can be detected at about 90 and 180 hr. respectively. The changes with time in the number of labelled cells show a difference dependent on the time of day of [3H]TdR administration. Both curves show an early doubling in labelled cells which then decline, forming a peak of labelled cells. A second peak occurs at about 120 hr. This is followed by a progressive decline with no further peak until values of about 1% labelling are obtained at 340 hr. These experiments have been investigated mathematically. A computer programme has been devized that permits all three types of experiments to be analyzed simultaneously. More importantly, it can analyse situations with a heterogeneity in cell cycle parameters in all proliferative subpopulations. Various models for epidermal cell replacement have been considered. The data as a whole can best be explained if the basal layer contains at least two distinct subpopulations of cells and an exponentially decaying post-mitotic population with a half-life of about 30 hr. The proliferative sub-populations must be characterized by near integer differences in the length of cycle, the precursor (stem) compartment having the longer cycle. An inverse relationship is required for the length of S, i.e. the shortest time for the stem cells. A full range of cell kinetic parameters can be calculated and are tabulated for the most appropriate model system which is one involving three transit proliferating subpopulations.

Animals↗
PubMed1982

The spatial organization of the hierarchical proliferative cells of the crypts of the small intestine into clusters of 'synchronized' cells.

A statistical analysis of the distribution of [3H]TdR-labelled cells in longitudinal and transverse sections of crypts from the ileum of the mouse, indicated that there was a strong tendency for labelled or unlabelled cells to be associated in short vertical runs and lateral clumps, suggesting the presence of clusters of labelled cells on the sides of the crypts. A model is discussed for the cellular spatial organization of the crypt that proposes a vertical alignment of the cells within branches of the proliferative cell lineage. The model would predict vertical alignment of partially synchronized cells as well as some lateral clumping. In the present studies mitoses were not observed at higher levels in the crypt than labelled (S phase) cells. This observation would be predicted by the non-random spatial organization suggested by the model. The model would also make certain predictions concerning cell migration. These are discussed in relation to cell migration studies which include evidence that migration continues in the absence of mitotic activity.

Animals↗
PubMed1981

Effect of low dose ionizing radiation on the murine pericryptal fibroblast sheath: radiation damage in a mesenchymal system in vivo.

The effect of low dose ionizing radiation from a variety of sources on the murine small intestinal and colonic pericryptal fibroblast sheath (PCFS) has been investigated. Ultrastructural and light microscopic changes seen within 3 hours after radiation resembles the mode of cell death known as apoptosis. The apoptotic index (AI) was shown to rise steadily for 4 hours after irradiation, and then to return to control levels by 10 hours. 137Cs gamma-irradiation over a range of doses from 0-803 cGy caused an increase in AI from control values of 1-2 per cent to a plateau level of approximately 8.5 per cent for doses above 40 cGy. Investigation of the response of the PCFS to doses of 137Cs and 60Co gamma-irradiation and X-irradiation below 40 cGy demonstrated a steady increase with dose in AI. The survival curve for the radiosensitive subpopulation susceptible to death through apoptosis as a consequence of exposure to non-acute doses of radiation has a D0 of 10.6 cGy and an extrapolation number of 2.3.

Animals↗
PubMed1981

Polyploidy in the murine colonic pericryptal fibroblast sheath.

The cause of the apparently paradoxical occurrence of relatively high levels of labelling and low levels of mitotic activity in the pericryptal fibroblast sheath (PCFS) was investigated. Analysis of the distribution of grain densities over epithelial cells and the PCFS in the colon demonstrated that, although the former had a unimodal peak, the PCFS had a multi-peak distribution. The PCFS nuclei with the higher grain densities gradually disappeared with time, due not to proliferation but to lateral migration into the lamina propria. Photodensitometric analysis confirmed the existence of polyploid cells in the colonic PCFS, but not in the epithelium.

Animals↗