Epidermal Cell Production Research Articles

The decrease in growth of phosphorus‐deficient maize leaves is related to a lower cell production

ABSTRACTThe spatial distribution of leaf elongation and adaxial epidermal cell production in leaf 6 of maize (Zea mays L. cv. Cecilia) plants grown in a growth chamber under two contrasting availabilities of P in the soil was investigated. Lower displacement velocities from 32.5 mm from leaf base and a shorter growth zone were found in low P (LP) leaves compared with control leaves. P deficiency significantly diminished maximum relative elemental growth rate and shifted its location closer to the leaf base. Cells were significantly longer in LP than in control leaves for all positions from the leaf base except at the end of the growth zone. For both treatments it took a similar time for a cell situated at the leaf base to reach the limit of the growth zone. The average length of the cell division zone was decreased by 21% in LP leaves. Significant differences were found in cell production and cell division rates from 12.5 mm from the leaf base although maximum values were similar between P treatments. A shorter zone of cell division with lower cell production rates along most of its length was the regulatory event that decreased cell production, and ultimately leaf elongation rates, in P‐deficient maize plants.

Corneocyte desquamation.

Corneocyte desquamation at the skin surface is a complex biologic event which is normally regulated for providing an inconspicuous shedding of single corneocytes. When altered, the process gives rise to xerotic and ichthyotic conditions. The present review focusses on important biologic and molecular aspects responsible for normal and altered corneocyte desquamation. There is a complex relationship between epidermal cell production, maturation and desquamative loss. Corneocyte hydration, stratum corneum barrier function and enzymatic corneodesmolysis are involved in a dynamic interrelationship. Many physiological and environmental factors acting in a different time frame influence desquamation.

Low Cell‐Wall Extensibility Can Limit Maximum Leaf Growth Rates in Rice

The aim of this research was to clarify physiological mechanisms underlying slower leaf growth rates in rice(Oryza sativa L.) as compared with maize (Zea mays L.) and barley (Hordeum vulgare L). Seedlings were grown under controlled‐environment conditions with adequate supplies of water and mineral nutrients. The growth rates of emerging first leaves in both paddy and upland rice were low by comparison with maize and barley genotypes. The possibility that differences in mature cell size, comparative cell production rates, osmotic potentials, or extensibility characteristics of growing cell walls were involved in regulating these species differences were investigated. The lower growth rate of the rice leaves was not associated with comparatively lower rates of epidermal cell production but was associated with the production of smaller mature cells. The smaller size of the rice leaf cells was not associated with less negative osmotic potentials in the cell‐expansion zone. However, the comparative extensibilities of the growing leaf tissues and cell walls decreased in the order barley > maize > rice and gave good linear correlations with leaf relative‐growth rates (r = 0.87** and 0.97**, respectively). The data suggest that exceptionally low cell‐wall extensibility is involved in limiting maximum leaf growth rates in rice. Future introduction of increased wall extensibility in paddy rice might lead to increases in leaf growth potential and conceivably to improved yields.

Differential Regulation of Epidermal Cell Tumor-Antigen Presentation by IL-1α and IL-1β

IL-1 exists in two forms, termed IL-1alpha and IL-1beta, which exert similar effects in a number of biologic models. Recently, there have been reports of some differences in the activities of these two species in some systems. To address this issue with regard to Langerhans cells, Langerhans cell-enriched preparations of epidermal cells were treated with either IL-1alpha or IL-1beta before pulsing with S1509a tumor-associated antigens and subsequent use for immunization of naive mice to S1509a. While epidermal cells treated with 100 U IL-1beta per ml were able to induce protective tumor immunity (as indicated by the rejection of a subsequent tumor challenge with viable S1509a tumor cells), epidermal cells treated with 100 U IL-1alpha per ml failed to confer protective immunity. At 1000 U per ml, IL-1beta also inhibited the ability of epidermal cells to induce tumor immunity. To investigate the effects of the two IL-1 forms on elicitation of tumor immunity, naive mice were immunized against the S1509a tumor by s.c. injection of dead S1509a cells. Epidermal cells enriched for Langerhans cells were treated with either 100 U IL-1alpha or IL-1beta per ml before tumor-associated antigens-pulsing. Epidermal cells were then washed and injected into a hind footpad of tumor immune mice and 24 h footpad swelling was assessed as a measure of delayed-type hypersensitivity. Exposure to IL-1alpha led to suppressed elicitation of delayed-type hypersensitivity, whereas IL-1beta treated epidermal cells elicited a normal (100 U per ml) or enhanced (1000 U per ml) level of delayed-type hypersensitivity. Previous experiments indicated that the suppressive effects of IL-1alpha on induction of immunity may be mediated by TNF alpha. Therefore, the ability of IL-1alpha or IL-1beta to induce epidermal cell production of TNF alpha was assessed. IL-1alpha induced epidermal cells to secrete significantly higher amounts of TNF alpha protein compared with stimulation with IL-1beta. IL-1alpha and IL-1beta appear to differentially regulate epidermal cell antigen presenting capability.

Studies on the effects of topical retinoic acid on photoageing

Tretinoin has been previously shown in animal and clinical studies to stimulate epidermal cell production and to be effective in the treatment of solar keratoses. A double-blind, placebo-controlled study confirmed that topical tretinoin produced an overall improvement in photoaged skin and decreased solar keratoses. There is no evidence that tretinoin has an irritative effect, nor is there any evidence that the improvement in appearance is due to oedema.

Techniques for assessing the activity of topically applied retinoids

The retinoid drugs have profound effects on many aspects of skin biology. The exact activity profile depends on the particular analog and its route of administration. The topical retinoids used at present have marked therapeutic effects on epidermal cell production and desquamation. All- trans-retinoic acid (tretinoin) also acts on dermal connective tissue and microvasculature in a way that is less well established but may also be of therapeutic benefit. We investigated both tretinoin and motretinide in normal subjects and in patients with ichthyosis. The quantitative dansyl chloride test has been particularly useful in monitoring the desquamatory action of these topically applied retinoids. Both compounds resulted in enhanced rates of epidermopoiesis and desquamation. Marked changes in the cytochemical profile of the epidermis were also detected, changes that differed somewhat from the alterations induced by the systemic administration of etretinate. Changes in dermal structure and vascularization were monitored by A-scan ultrasound and laser Doppler flowmetry. However, only minor changes were recorded, probably because of the comparatively short application time. These newer techniques for investigating skin structure and function offer considerable opportunities for delineating the action of retinoids.

The epidermal engine: a commentary on epidermopoiesis, desquamation and their interrelationships

Synopsis The physiology and methods for study of epidermal cell production are reviewed. The importance of desquamation to any consideration of epidermal cell population size is stressed. Techniques for the measurement of the rate of desquamation are described with particular emphasis on quantitative dansyl chloride clearance time methods. Although the rates of cell production and cell loss must be related, the possibility of aberrations from a strict equivalence are discussed. Finally, the questions of the control of epidermopoiesis and the changes that occur with ageing are discussed. La fonction épidermique.

The effects of an aromatic retinoid (etretinate) on epidermal cell production and metabolism in normal and ichthyotic patients.

Normal subjects and ichthyotic patients were biopsied before and after etretinate (Tigason) therapy. Histometric and cell kinetic measurements showed minimal changes following treatment. The metabolic activity across the epidermis was measured by a novel approach using the Quantimet 720 image analyser, and was significantly increased in the normal subjects as demonstrated by glucose-6-phosphate dehydrogenase (G6PDH), succinic dehydrogenase (SDH) and non-specific esterase (NSE) activities. In the ichthyotics studied the levels of G6PDH and SDH activity were significantly lowered following etretinate therapy, to levels similar to those demonstrated in normal subjects. In contrast, the activity of NSE was increased in the ichthyotics after etretinate therapy. It is suggested that the effect of retinoids is to 'normalize' the process of epidermal differentiation when it is abnormal.

Plantar Hyperkeratosis: A Study of Callosities and Normal Plantar Skin

Although callosities of the plantar skin are common and often disabling, little is known of their pathology or the reasons for their persistence. In this study plantar epidermal structure and cell renewal were investigated in patients with callosities and normal, age-, sex- and site-matched control subjects. Tritiated thymidine autoradiographic labeling indices were increased in the calluses but the dansyl chloride fluorescence clearance time was prolonged, reflecting the increased thickness of the stratum corneum. The number of corneocytes that could be removed from the surface of callosities by a standardized stimulus was considerably increased compared to controls but after adhesive tape stripping no such increase was observed. The density of corneocytes as measured on Percoll gradients was decreased in corneocytes from callus compared to normal plantar skin, and their volume was increased. These observations suggest that there are differences in epidermal differentiation due to an increased rate of epidermal cell production in plantar skin affected by callosity.

Pityriasis rubra pilaris: epidermal cell kinetics

Epidermal proliferative kinetics were studied in a patient with pityriasis rubra pilaris. Elevated proliferative indices (flash labelling and mitotic indices) were apparent compared with normal epidermis and measurements of the birth rate indicate that the rate of epidermal cell production was similar to that found in psoriasis, and equalled 11.8 cells/1000 germinative cells/h; this suggests a cell cycle time of 60 h. Contemporaneous measurements of the rate of entry into DNA synthesis showed values similar to the rate of entry into mitosis; hence there is no G2 cell loss as appears to occur in the hyperproliferative psoriatic epidermis.

Epidermal abnormalities in Refsum's disease

A female patient with severe Refsum's disease is described. She had striking ichthyosis and detailed investigations into the structure of the epidermis were performed. Light microscopy and transmission electron microscopy revealed lipid-containing vacuoles in the epidermis. Scanning electron microscopy of the stratum corneum showed disruption and the presence of microvilli on individual horn cells consistent with a high output state of epidermal cell production.

Hair follicle kinetics in psoriasis.

The rate of epidermal cell production has been measured in the various parts of scalp hair follicles in patients with psoriasis of the scalp, and in controls with normal scalp skin. An in vitro technique was used in which thin tissue slices were exposed to tritiated thymidine enabling cells about to divide to become autoradiographically labelled. Biopsies from thirteen patients with psoriasis and nine controls were examined in this way. The labelling indices of the interfollicular epidermis was 27-5% in the psoriatics and 9-5% in the controls. The upper part of the external root sheath had a labelling index of 28% in the psoriatic group compared to 13-9% for the controls. The labelling indices of the sebaceous glands, matrices and external root sheaths were very similar in the two groups. The findings support the hypothesis for a dermal stimulating influence causing the increased epidermopoiesis seen in psoriasis.