Epidermal Cell Populations Research Articles

Some old concepts and new findings on hormonal control of insect morphogenesis

By means of the artificially induced heterochronic developmental deviations represented by local prothetelies and metathetelies it has been possible to investigate the individual developmental fates of ontogenetically different tissues, such as larval, pupal, and adult epidermal cells, in one and the same body and under the identical concentration of juvenile hormone (JH) in the haemolymph. In contrast to the widely accepted hormonal theories which claim that the kind of morphogenesis is determined by large, intermediate, and low titres of JH, the heterochronic character of the tissues never developed into a uniform population of homomorphic epidermal cells. Instead, in the presence of effective amounts of JH the heterochronic pattern has been fully preserved and carried on into the next developmental instar. Moreover, in the absence of the effective JH amounts the ontogenetically different tissues, such as larval and pupal epidermal cells, simultaneously undergo their respective morphogenetic developments, i.e. larval-pupal and pupal-adult morphogenesis in the same hormonal milieu. It is concluded that the selective factor in determination of the kind of morphogenetical changes is not an altered JH titre but the extant, previously attained degree of ontogenetic structural differentiation. It has been demonstrated that JH can temporarily and reversibly inhibit the morphogenetic progress at quite different ontogenetic levels but it cannot cause a ‘reversal of metamorphosis’ at any of these levels. Under specific experimental conditions the larval epidermal cells can undergo pupal and adult morphogenesis without secreting the pupal cuticle. However, the pupal morphogenetic interstage, whether with the cuticle or without the pupal cuticle, constitutes an obligatory developmental step. Further, it appears that an absence of JH may represent an important condition but not a real cause of insect metamorphosis, as presumed in some other hormonal concepts. Thus, chromosomal duplications or cellular divisions in the absence of JH have not committed the cells to morphogenesis unless provided by an additional stimulus of endogenous prothoracic gland hormone or exogenous ecdysterone. An important factor in understanding the hormonal control of insect morphogenesis is the critical timing of the respective morphogenetic steps. This corresponds closely with the duration of the pharate phases in insect development. Possible hormonal mechanisms concerned in the regulation of morphogenesis in endopterygote insects have been outlined.

The development of skin mucous glands ofXenopus laevis during metamorphosis.

As the number of multicellular mucous glands increases in the skin ofXenopus laevis larvae during metamorphosis, the acid mucopolysaccharide (AMPS) content of the skin increases also. Purification of this skin AMPS by polyacrylamide gel electrophoresis revealed a major band characteristic of adult mucous secretion. Incorporation of14C-galactose into this band increases during metamorphosis, but there is still a substantial synthesis of this material in premetamorphic skin that lacks mature mucous glands. This raises the question of whether the epidermal cells that had been making mucus in premetamorphic skin stop this activity as mucous glands develop, or whether they are discarded and replaced by a new population of epidermal cells that do not make mucus unless they develop into a mucous gland.

Epidermal-cell population changes produced by exposure to 2,300 R.

HomeRadiologyVol. 103, No. 1 PreviousNext Radiation BiologyEpidermal-Cell Population Changes Produced by Exposure to 2,300 RJohn O. Archambeau, Anne Gerber, Rafik Ayoub, Harry J. BrenneisJohn O. Archambeau, Anne Gerber, Rafik Ayoub, Harry J. BrenneisAuthor Affiliations Department of Therapeutic Radiology Nassau County Medical CenterEast Meadow, N. Y. 11554John O. ArchambeauAnne GerberRafik AyoubHarry J. BrenneisPublished Online:Apr 1 1972https://doi.org/10.1148/103.1.191MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In AbstractThe histological changes produced by irradiation of a 10 cm (diameter) field on the shoulder of immature swine could be divided into degenerative and regenerative phases. The degenerative phase was characterized by progressive cell loss, increased nuclear volume, and a lower mitotic index. The cell loss was complete or maximal by twenty-one days. The regenerative phase was characterized by discrete islands of proliferating cells, first seen at twenty-one days. These islands increased in diameter; by twenty-eight days they had fused into a re-epithelialized surface which then became hyperplastic. The apparent doubling time of the regenerating phase was 3.3 days.Article HistoryPublished in print: Apr 1972 FiguresReferencesRelatedDetailsCited ByChanges in epidermal radiosensitivity with time associated with increased colony numbersThe British Journal of Radiology, Vol. 74, No. 881Recommended Articles RSNA Education Exhibits RSNA Case Collection Vol. 103, No. 1 Metrics Altmetric Score PDF download

Correlation of Initial Changes in the Mouse Epidermal Cell Population with Two Stage Carcinogenesis—A Quantitative Study

The behaviour of the normal epidermis of mice on the first 5 days of exposure to a single application of carcinogens and cocarcinogens has been investigated by simple quantitative measurements of cell population, size of cells and thickness of the epidermis. Irritant substances and promoting agents both produce cellular hypertrophy but the respective responses can be distinguished by the much greater incidence of degenerate cells associated with irritant treatment. Urethane treatment is characterized by induction of a transient hypoplasia which is not in agreement with the level of cellular division. This response has also been demonstrated after treatment with mild carcinogens or low doses of potent carcinogens. Higher dose levels are followed by a reduction in the mitotic index after about 27 hours. The possibility of developing a preliminary screening test for carcinogenic substances is discussed in the light of these observations.

Experimental approach to the renewal of the skin surface.

THE population of epidermal cells can be regarded as a steady state system which converts various metabolites into keratin. On this basis it can be postulated that the keratin output may not exceed the metabolic input of the epidermis. In addition, if a valid comparison can be drawn between the epidermis and other steady state cellular systems1,2, variations in the magnitude of the nutritive flux may determine not only the rate of proliferation but also the steady state size of the population. This view in no way negates the possible involvement of specific growth regulatory substances3,4, nor can an unequivocal demonstration of the presence of such hormones in normal skin violate the input–output relation.

Epidermal cell population kinetics after repeated applications of some hyperplasia-producing substances

The initial and the long term effects of repeated surface applications to the skin of hairless mice (hr/hr) of benzene, cantharidin in benzene, and 20-methylcholanthrene, respectively, have been examined. The growth parameters have been evaluated by means of the Colcemid method. The reactions of the epidermal cell population have been interpreted from cybernetic point of view and as biological phenomena. Both benzene and cantharidin provoked alterations in the dynamics of the epidermal cell population that can readily be explained in terms of cybernetics. The initial reaction after application of methylcholanthrene was also in conformity with this concept, but later on after treatment with this agent a striking prolongation of the mitotic duration was observed in spite of the fact that the mitotic rate was increased too. These findings were difficult to reconcile with the simple cybernetic system. Other mechanisms must be discovered. Some possible explanations are discussed.

Epidermal cell population kinetics in albino guinea-pig skin.

IN adult mammals the epidermal cell population is in a steady state—continuous cell loss by keratinization is balanced quantitatively by new cell production in the basal layer. We have found that the turnover time of albino guinea-pig epidermis (time required for the replacement of a number of cells equal to that present in the basal, spinous and granular layers) differed from that reported by Platt1 and also from that found for other mammals 2–5.

Epidermal cell population kinetics after a single application of some hyperplasia-producing substances

The initial and the long term effects of a single topical surface application to the skin of hairless mice (hr/hr) of benzene, cantharidin in benzene, and 21-methylcholanthrene in benzene, have been examined. The growth parameters have been evaluated by means of the Colcemid method, which is briefly discussed. The reactions of the epidermal cell population have been interpreted as biological phenomena and in terms of cybernetics. Both benzene and cantharidin provoke alterations in the dynamics of the epidermal cell population that are well compatible with a simple regenerative reaction and can readily be explained in terms of cybernetics. The initial reaction after application of methylcholanthrene was also in conformity with this concept, while the later alterations cannot well be explained as a regenerative reaction. Some other mechanisms appear to be involved. An inverse relationship between the mitotic rate and the mitotic duration could be discerned in all reactions that could be interpreted as simple regenerative reactions. The alterations in the various growth parameters indicated that the mitotic rate might be regulated by a derivative type of negative feedback control, and the mitotic duration by a proportional type.

The Ichthyosiform Dermatoses II: Autoradiographic Studies of Epidermal Proliferation

The Ichthyosiform Dermatoses II: Autoradiographic Studies of Epidermal Proliferation

A Histochemical Study of Polyphosphate Hydrolases in Epidermal Dendritic Cells

A Histochemical Study of Polyphosphate Hydrolases in Epidermal Dendritic Cells

Mitotic Rates of Rat Epidermis

Adult epidermal tissues are renewing cell populations. Mitosis continuously provides new cells replacing those that became keratinized and ultimately shed. It seems plausible to assume that in the epidermis of growing individuals mitosis supplies cells both for cell addition (growth) and renewal. During growth, more cells are presumably retained in the tissue than become lost through desquamation. It is feasible by cutaneous incision to temporarily revert adult epidermis into a growing cell population. Presumably also during healing, cell production exceeds cell loss. What is the magnitude of cell production for renewal of adult epidermis, for simultaneous cell addition and renewal during growth, as well as during epidermal regeneration? To elucidate these problems, the mitotic rates of three epidermal cell populations (ear, plantar, and abdominal epidermis) were determined in the growing, adult, and senile rat. Further, the adult ear and back skin epidermis was converted by cutaneous incision into regenerating cell populations, and the mitotic rates were determined during healing at intervals from six hours to nine days.

The re-formation of the epidermis of embryonic Rana pipiens following treatment with ultrasound

The hypothesis is tested that mitotic activity is responsible for epidermal stratification by increasing the density of cells in a cell layer and thereby promoting cell migration out of this layer. The stratification process was observed in the epidermis of Rana pipiens embryos following treatment with ultrasound which causes the shedding of the periderm; the single layer of residual cells gives rise to two cell layers by the end of the first day after this treatment. The density of epidermal cells was observed in whole mounts of tail epidermis. The epidermal cell density of sonicated animals decreased during the first day so that the cells in both layers were only half as densely packed as those in the control epidermis. Changes in the cell density, therefore, could not be responsible for peridermal re-formation. Equations for the total number of epidermal cells on one side of the tail as a function of time were derived by multiplying corresponding functions for cell density by those for the surface area of one side of the tail. The rates at which cells were added to the epidermal cell population by mitosis were calculated from the mitotic index divided by the duration of mitosis and were used to estimate the percentages of cells added by mitosis during the first day. Only one-third of the tail epidermal cells of sonicated animals divided during the first day. Since there were about as many cells in the periderm as in the basal layer at that time, at least 33% of the new peridermal cells had migrated out of the basal layer without having been replaced there by cell division. Cell division, therefore, could not be responsible for peridermal re-formation. The hypothesis is thus rejected. Epidermal cells evidently migrated into two layers from the original single layer of residual cells irrespective of the cell density and of cell division.

Deoxyribonucleic Acid Content of Basal Cells of Mouse Epidermis

STUDIES on mouse-ear and body-skin epidermis have led Gelfant1,2 to the conclusion that there are two distinct populations of epidermal cells, one with a G2 period of a few hours, the other with a G2 period as long as five days. Bullough3 has commented on the work of Gelfant and stated that his results are statistically inadequate. In view of the general uniformity in length of the G2 period in mammalian cells studied so far4 of approximately 2–4 h, the existence of a population of cells with an unusually long G2 period is of some importance. It seemed worth while, therefore, to determine the distribution of DNA levels in epidermal cells, using a densitometric method, since a pronounced peak would be found at the tetraploid level if a sizeable population of cells were in the G2 state.

Growth and deposition of resilin and chitin in locust rubber-like cuticle

Because of its simplicity, rubber-like cuticle offers good opportunities for studying problems of cuticle growth and deposition. Progress in this direction should lend impetus to subsequent studies of the more intricate solid cuticle. Although differing widely in physical and chemical properties, rubber-like and solid cuticles may nevertheless be compared with regard to their units and cycles of deposition. The growth of the protein rubber resilin and chitin has been measured quantitatively in two samples of rubber-like cuticle, and the results confirmed in sections analysed stratigraphically by means of daily growth layers. The cross-linking of the peptide chains of resilin, which establishes its three-dimensional molecular network, occurs continuously with deposition, in marked contrast to the bulk-tanning processes of solid exocuticle. Chitin deposition in rubber-like cuticle is quantal in nature, each chitin lamella representing a constant weight of chitin secreted by a constant population of epidermal cells. The deposition frequency of chitin lamellae is given as a function of age. Resilin and chitin deposition are analysed at the cellular level and a new perspective of cuticle growth is briefly outlined.

Initiation of mitosis in relation to the cell division cycle

This report examined the question of when mitosis is initiated during the cell division cycle in mouse ear epidermal cells. Mitosis was selectively initiated and controlled by cutting one ear and leaving the other ear intact. The various stages of the cell cycle, G 1 S, and G 2 were distinguished by labeling DNA with tritiated thymidine and then making autoradiographic counts of labeled interphase nuclei and of labeled and unlabeled mitoses collected by colchicine. The following points were established. 1. 1. A unique population of epidermal cells was discovered that does not pass through an automatic cycle of cell division, but rather holds up in the G 2 phase for long periods of time. These cells are ready to divide within relatively short notice and can be specifically induced to do so by cutting the ear. Thus, mitosis can be initiated from the G 2 phase of the cell division cycle. 2. 2. Cutting also stimulates another population of epidermal cells that were in the G 1 phase of the cell cycle. These cells begin to synthesize DNA within 1 hr after the cutting stimulus. 3. 3. A concept of cell renewal was proposed of a population of cells that serves as a fast-acting renewing system in tissues with a slow-acting renewal rate.