In vivo effects of epidermal growth factor on epidermal pattern formation and hair follicle initiation in the marsupial bandicoot Isoodon macrourus.

The extrauterine development of marsupial pouch young (northern brown bandicoot Isoodon macrourus) has facilitated the study of the effects of murine epidermal growth factor (mEGF) on pattern formation in skin. Hair follicle initiation and development, which in the mouse would occur from about Days 13-14 of gestation onward, occurs postnatally. In the present study the effect in vivo of mEGF on developing skin corresponding to mouse gestational ages from Day 13 onward was examined. Subcutaneous injections of mEGF (0.5, 1.0 and 2.0 microg g[-1] body weight) or equivalent volumes of saline (0.9% w/w) were administered daily, before and during hair follicle initiation and development. Murine EGF inhibited the formation of hair follicles, hair follicle sweat glands, sebaceous glands and dermal papillae. The pattern of follicle initiation was perturbed. The characteristic trio follicle grouping was absent, and follicle rudiment densities (no. per mm2 skin surface) were significantly lower in animals treated with mEGF, whereas follicle diameters were increased. These data may reflect a role for the epidermal growth factor (EGF) receptor in epidermal pattern formation. The EGF receptor and its potential ligands (such as EGF, transforming growth factor (TGF-alpha) or other yet-to-be-discovered ligands) perhaps act as parts of a pattern-forming system in vertebrate skin.

Ultrastructural changes in epidermal Langerhans cells and melanocytes in response to ultraviolet irradiation, in Australians of Aboriginal and Celtic descent.

The effects of exposure to small doses of artificial ultraviolet radiation (UVR) on the ultrastructure of epidermal Langerhans cells (LC) and melanocytes were studied in two groups of Australian subjects, one of Aboriginal and the other of Celtic descent. UV exposure induced an apparent depletion of LC in the epidermis of both groups. However, LC depletion in the Aboriginal subjects was associated with apoptosis, whereas organelle and membrane disruption in the LC of Celtic subjects suggested a reduction by direct cellular damage. LC in Aboriginal epidermis tended to become relocated at more superficial levels following UV exposure, and their Birbeck granules became more numerous. LC in Celtic epidermis appeared to become relocated in a basal location and contained fewer Birbeck granules. The central lamina of the Birbeck granules in Aboriginal LC, which was more electron-dense than that in Celtic subjects prior to UV treatment, was temporarily lost following treatment, while the ultrastructure of Birbeck granules in Celtic LC was unchanged. LC and 'indeterminate cells' in intimate association with lymphocyte-like cells occurred in the basal layer of Celtic epidermis 5 days after exposure. These complexes were not observed in Aboriginal epidermis although isolated lymphocyte-like cells were observed in the same location. Melanocytes in Aboriginal epidermis contained greater numbers of melanosomes than those in Celtic epidermis throughout the experiment. Inactive epidermal melanocytes in Celtic subjects initially responded to UV exposure with a slight increase in melanosome content followed by a substantial further increase, whereas active melanocytes in the Aboriginal subjects showed the opposite response. The implications of the different responses of LC and melanocytes in the two groups, in relation to immunological function of the epidermis and the marked racial difference in the incidence of skin cancer, are discussed. Cancer of the skin, particularly basal and squamous cell carcinoma, occurs primarily in people with fair skin who burn easily following exposure to ultraviolet radiation (UVR). In contrast, the incidence of skin cancer in inherently dark-skinned people is low. Melanin is synthesized by melanocytes in response to UVR and is thought to protect epidermal cells against damage to their genetic material by absorbing UVR and thereby reducing its penetration into the skin. Thus darkly pigmented skin is more resistant to the effects of UVR.(ABSTRACT TRUNCATED AT 400 WORDS)

Apoptosis in wool follicles during mouse epidermal growth factor (mEGF)-induced catagen regression.

Depilatory infusions of mouse epidermal growth factor (mEGF) induced regressive involution (catagen) in the wool follicles of Merino sheep. The follicles were examined by transmission electron microscopy prior to infusion and at intervals during catagen regression in order to determine the mechanism(s) involved in follicle involution. Cell deletion by apoptosis occurred in all cell types in the proximal region of catagen follicles between 12 h and 6 days after the beginning of infusion. Apoptosis also occurred in the basal layer of involuting sebaceous glands at 2 and 3 days, following earlier mEGF-induced proliferation. This process involved nuclear chromatin condensation and margination in single, scattered cells which subsequently fragmented and were ultimately phagocytosed and degraded by adjacent unaffected cells. It was concluded that during mEGF-induced catagen, wool follicle involution was accomplished largely through cell death and deletion by apoptosis.

Effects of exposure to ultraviolet light on epidermal Langerhans cells and melanocytes in Australians of aboriginal, Asian and Celtic descent.

The effects of 3 daily, 7-min exposures to artificial ultraviolet light (UVL), designed to simulate natural sunlight, on epidermal Langerhans cells (LC) and melanocytes were studied in 17 healthy Australian volunteers of differing skin pigmentation. Six were of Celtic, 6 of Asian and 5 of Aboriginal descent. LC were visualized using the immunofluorescence method for HLA-DR and T6 antigens, and the histochemical method for ATPase. UVL induced a transient reduction in the LC population density and an increase in the number of melanocytes in all subject groups. The reduction in number of immunocompetent LC or the disruption of their surface markers was greatest in the Celtic subjects, who had the fairest skin, and least in the Aboriginal and Asian subjects, who had the darkest skin. However, neither the inherently dark skin pigmentation nor the UVL-induced increase in pigmentation were sufficient to prevent the depletion of immunocompetent epidermal LC. Non-dendritic, rounded cells and very large dendritic, non-LC, which were present in the epidermis of some subjects, were stimulated to increase in number by exposure to UVL. The identity and function of these cells is uncertain and they require further investigation.

Effects of sunlight exposure on Langerhans cells and melanocytes in human epidermis.

The effects of 12 daily, half-hour exposures to sunlight on epidermal Langerhans cells (LC), and melanocytes were studied in 31 healthy volunteers. Nineteen were of Celtic and 12 of mixed European descent. Sunlight appeared to have both a direct, transient, detrimental effect and an indirect stimulating effect on the LC, and a direct and an indirect stimulating effect on the melanocytes. The mixed Europeans had a somewhat greater increase in the melanocyte population density following exposure to sunlight than the Celts. However, the number of LC fell following sunlight exposure regardless of the melanocyte response. Thus the melanocytes did not appear to provide the LC with immediate protection from ultraviolet light.

Ultrastructural changes in the oviductal epithelium of Merino ewes during the estrous cycle.

Isthmic and ampullary oviductal epithelia sampled from Merino ewes at days -1, 1, 3, and 10 of the estrous cycle (estrus = day 0) were studied by scanning and transmission electron microscopy after fixation by vascular perfusion. Secretory cells, ciliated cells, and lymphocytelike basal cells were observed in both isthmic and ampullary epithelium at all stages of the estrous cycle studied and their ultrastructural features were analyzed. Synthesis of lamellated secretory granules occurred in the ampullary secretory cells during the follicular and early luteal phases, and their contents were released by exocytosis into the oviductal lumen during the luteal phase. Granule release was associated with nucleated apical protrusion of these cells into the oviductal lumen. No such secretory activity was displayed by isthmic secretory cells even though a few cells contained nonlamellated granules. Apocrine release of apical vesicles and accompanying cytoplasmic material from apical protrusions of ciliated cells occurred in the isthmus around estrus but not in the ampulla. This unexpected feature has not previously been reported in any other mammal. Dendritic basal cells were distinguished in the lower part of the epithelium by their heterochromatic nuclei, electron-lucent cytoplasm, and lack of attachment zones. No migration of basal cells was observed, and their ultrastructural features were similar in the ampulla and isthmus and at all stages of the estrous cycle examined. The function of these lymphocytelike cells in the epithelium is uncertain, but the presence of phagocytic bodies and lysosomes in 20% of them may indicate a phagocytic role.

Morphological changes in the skin and wool fibres of Merino sheep infused with mouse epidermal growth factor.

Intravenous infusion of 4.5-4.7 mg of mouse epidermal growth factor (mEGF) into nine castrated male Merino sheep for 26 h resulted in complete casting of the fleeces 6-8 days later. The morphological changes which occurred in the skin were studied in skin samples taken before infusion and at intervals between 1 h and 42 days after the infusion had begun. Wool fibres from the shed fleeces were examined with the scanning electron microscope. Increased cell proliferation occurred in the epidermis and sebaceous glands, whereas the wool follicles regressed. Transient dermal haemorrhages occurred during the first 3 h of infusion. The fibre and inner root sheath in the keratogenous zone of 30-40% of the follicles were partially disrupted within the first 6 h of mEGF infusion; catagen began in all follicle bulbs within 24 h. Fibre and inner root sheath production, although markedly reduced, continued in about 60% of follicles which had partially regressed, but production ceased in the remainder in which tapered ends formed on the fibres prior to shedding. Follicles began to regenerate asynchronously 4-8 days after the beginning of infusion and completed their development during the next 3 weeks. The follicle regression and fleece casting induced by mEGF infusion, and subsequent follicle regeneration were completed more rapidly than observed previously with other depilatory agents, and, except for prolonged epidermal thickening, there was no lasting cutaneous abnormality.

Observations on Graafian follicles and their oocytes during lactation and after the removal of pouch young in the marsupials Isoodon macrourus and Perameles nasuta.

Ovaries from 63 bandicoots (Isoodon macrourus and Perameles nasuta) were collected in order to obtain Graafian follicles close to ovulation for light and electron microscopy. During the first 42 days of lactation (lactation c. 60 days), the follicles were less than 1.0 mm in diameter, whereas from 43 to 52 days, some animals had follicles up to 2.0 mm in diameter, or ovulation had occurred and new corpora lutea were present. This ovulation was associated with the lactation estrus that occurred in some animals. In general, the largest Graafian follicles of the bandicoots were morphologically similar and resembled those of many other mammals. These follicles protruded from the surface of the ovary and revealed a conspicuous theca interna. The granulosa cells exhibited an unusual feature in that they contained masses of glycogen, often associated with lipid droplets and filaments. The oocytes were similar in size (diameter c. 150 microns) to those of some other marsupials and were surrounded by a zona pellucida and cumulus cells attached to the granulosa layer. The cumulus cells did not form a corona radiata as in eutherian mammals. The oocyte nuclei were somewhat flattened, peripherally located and similar in size (c. 40 x 19 microns) to those in other marsupials. These nuclei, which stained lightly with Azure A and were electron-lucent and homogeneous, were unusually irregular in contour. The nuclei were unique in that nucleoli were always absent. Small cytoplasmic bodies which may have been extruded nucleoli were found in the oocytes of I. macrourus, but not in P. nasuta. The cytoplasm in the bandicoot oocytes resembled that of other marsupials and some eutherians in that it was highly vacuolated with most of the organelles concentrated peripherally. Within the central region of the bandicoot oocytes there were crystalloids which were similar to those in oocytes of primordial follicles and in unilaminar blastocysts of I. macrourus.

Effects of experimentally induced fleece-rot on the structure of the skin of Merino sheep.

Four medium- and six strong-wool Merino sheep were exposed to continuous simulated rain (4 x 5 mm/h) for periods ranging from 3 to 9 days. In response, the sheep developed characteristics typical of fleece-rot lesions such as exudative encrustation and bacterial discoloration of the fleece. Skin samples were taken periodically for histological examination from the trunk region of the sheep prior to, during, and after wetting. An inflammatory response to wetting occurred in the upper layers of the dermis and this caused the release of cells which began invading the epidermis after only 6 h of wetting. An associated increased in vascular permeability was observed macroscopically following intravenous injection of Pontamine Blue dye. The incidence and extent of the inflammation increased during subsequent wetting while epidermal acanthosis and hyperkeratosis became increasingly evident. Epidermal thickness returned to pretreatment levels by 13 days after cessation of wetting when inflammatory regions were absent from most of the sheep. Cellular lysis occurred in the suprabulbar and keratogenous regions of a small proportion of follicles (1-13%) during wetting, resulting in the interruption of fibre growth and keratinization in these follicles and the occlusion of follicle hair canals with inner root sheath material ('plugs') which persisted after wetting ceased. These morphological changes in the epidermis, follicles and fleece are considered to occur as a consequence of the initial rapid inflammatory response to wetting during the developing of fleece-rot lesions.