Murray W. Hill

Connective tissue influences on patterns of epithelial architecture and keratinization in skin and oral mucosa of the adult mouse

SummaryEpithelial-mesenchymal interactions play an important role during embryogenesis but it is uncertain whether such interactions influence the maintenance of epithelial structure in the adult. To examine this problem, separated epithelial and connective tissue components of skin and mucosae from various regions of adult mice were homoor heterotypically recombined and transplanted to histocompatible hosts. The patterns of tissue architecture and keratinization of the resultant epithelia were examined for changes indicative of mesenchymal influences on the epithelial phenotype. Each type of epithelium, in some recombinations, fully conserved its normal pattern of phenotypic expression indicating that subepithelial connective tissue from all regions is permissive and that regionally-specific connective tissue influences are not necessary for conservation of epithelial specificity. In other recombinations, however, the epithelium acquired features of tissue architecture or keratinization typical of the epithelium normally associated with the connective tissue component, indicating directive influ ences from the connective tissue. The patterns of epithelial response observed suggest that there may be separate connective tissue influences on epithelial architecture and cytodifferentiation and that there is a regionally-related variation in the competence of epithelia to respond to these influences.

Maintenance of regionally specific patterns of cell proliferation and differentiation in transplanted skin and oral mucosa

SummarySpecimens of mouse ear, footpad and tail skin and palatal, buccal and lingual mucosae were transplanted to protected sites prepared in histocompatible hosts either as intact tissues or recombined after separation of epithelial and connective tissue components using EDTA. Despite maintenance in a protected ectopic site for up to 9 weeks, transplants maintained regionally specific differences in histological appearance and rates of mitotic activity. A diurnal variation in mitotic activity comparable to host control tissues was reestablished.

The influence of differing connective tissue substrates on the maintenance of adult stratified squamous epithelia

SummaryThe interaction between adult stratified squamous epithelium and its supporting connective tissue possibly involves both permissive and directive influences. To examine the effect of vitality and specificity of connective tissue on the maintenance of epithelial structure and histo-differentiation, specimens of skin and oral mucosa from various regions of adult mice were separated using either EDTA or trypsin. Prior to transplantation, the epithelium was recombined with either inverted homologous connective tissue or with connective tissue that had been killed either by heating or repeated freeze-thawing. Epithelial sheets were also transplanted onto the graft bed alone or in combination with striated muscle or tendon.Normal patterns of cytodifferentiation were maintained when the epithelium was recombined with inverted or frozen-thawed subepithelial connective tissue but there was a loss of spatial organization on the frozen-thawed connective tissue. In contrast, heat-killed or trypsin-treated frozen-thawed subepithelial connective tissue and non-dermal connective tissue failed to maintain a viable epithelium. These observations suggest that subepithelial connective tissues (dermis, lamina propria) but not deep connective tissues facilitate epithelial proliferation and histodifferentiation.

Age-associated changes in Langerhans cells of murine oral epithelium and epidermis

Oral mucosa and skin of older individuals are immunologically less responsive to a range of allergens, but it is not known whether this is due to changes in the number of Langerhans cells or to impaired cell function. EDTA-separated epithelial sheets from the cheek and palate mucosa, and from ear aN< footpad skin of three-month-old and 24-month-old C57BL/6NNia mice were stained for ATPase, beta-glucuronidase activity and Iab-surface antigen to demonstrate Langerhans cells. The general distribution of such cells was unchanged with age, but those in epithelia from the old mice were more varied in shape, with irregular celL bodies and more elongated dendritic processes. The numerical density of Langerhans cells in old mice was reduced by 30-59 per cent compared with that in young mice.

Influence of age on the morphology and transit time of murine stratified squamous epithelia

To determine whether stratified squamous epithelia from aged animals differ from those of young animals, specimens of skin from the pinna of the ear, the back and footpad and mucosa from the palate, cheek and ventral surface of the tongue were excised from 10 young (3-4 month-old) and 10 old (23-24 month-old) C57B1/6NNia mice and prepared for light microscopy. Tracings were prepared of the nucleated cell compartment and epithelial thickness, the number of nucleated cells/mm2 surface, the basement membrane: surface ratio, cell density and the number of basal cells/mm basement membrane were determined. To evaluate the epithelial labelling index and tissue renewal, a further group of young and old mice were injected with 1 microCi/g [3H]-thymidine and killed after 1 h or 2, 4, 5, 6 or 8 days and sections were prepared for autoradiography. Whereas the epidermis from the ear and footpad showed a statistically-significant increase in thickness, the epithelium from the palate was thinner in the old animals. The other tissues examined showed no change. Cell density decreased with age in the palate; cell size increased with age in the ear and footpad. No statistically-significant differences in labelling index or minimum transit time were observed between young and old animals in any of the tissues. Thus, there is no single age-associated change in epithelial structure or renewal common to all epithelia.

The influence of subepithelial connective tissues on epithelial proliferation in the adult mouse

SummarySubepithelial connective tissue is capable of modulating the pattern of histodifferentiation of stratified epithelia from adult animals, but it is not known whether the supporting connective tissue also influences epithelial proliferative activity. Epithelial and connective tissues of murine skin and oral mucosa, differing in their morphology and proliferative activity, were separated and heterotypically recombined prior to grafting to histocompatible hosts. After 3 or 8 weeks in situ, mitotic activity was determined following the administration of vinblastine sulfate. Although the mitotic activity in each of the epithelia could be modulated by some connective tissues, there was no distinct pattern of behavior. In combination with connective tissues from tongue or palate, the ear epidermis acquired a significantly increased mitotic activity. In contrast, when oral epithelia with high mitotic activity were recombined with dermal connective tissue, there was usually a significant reduction in proliferative activity. As there was no apparent association between mitotic activity and the induced changes in either organization or histodifferentiation, it is suggested that subepithelial connective tissue is capable of directly influencing the mitotic activity in the overlying epithelium.

Quantitative evaluation of regional differences between epithelia in the adult mouse

The composition and proliferation of skin from the ear, tail and footpad oral mucosa form the palate, cheek and tongue of adult mice were examined. The thickness of the nucleated cell layer of skin showed an approximately two-fold variation; a similar range was found between that of oral mucosae but that was considerably thicker than skin. No direct correlation between epithelial thickness and the number of nucleated cells was observed. Proliferative activity, assessed following the administration of vinblastine sulphate, and turnover of the epithelium showed a broad range of activities but more rapid in the oral epithelia than in the epidermis, suggesting a relationship between functional stress and proliferative activity. The criteria used clearly distinguish between morphologically different epithelia and should prove useful examining experimentally produced changes in epithelial histodifferentiation.

A quantitative ultrastructural analysis of changes in hamster cheek-pouch epithelium treated with vitamin A

SummaryThe ultrastructural changes induced by the topical application of retinol acetate on hamster cheek pouch epithelium were evaluated using stereological analysis. Electron micrographs were prepared of the basal and superficial regions of the nucleated cell layer of the epithelium obtained from 3 treated and 3 control animals and examined at two levels of magnification. A total of 528 micrographs were analyzed using a coherent double lattice test system. Although the mean thickness of the nucleated cell layer did not change significantly after 10 days of treatment with retinol acetate the formation of keratinized squames was completely inhibited. This was paralleled by significant changes in the volume density of a number of organelles in both the basal and superficial strata. Rough endoplasmic reticulum increased significantly whereas filaments, which maintained a constant diameter of approximately 9 nm, keratohyalin granules and membrane-coating granules decreased in both strata. Desmosomes also showed a significant decrease in numerical area density in the treated tissues. In contrast, no changes were observed in the volume density of the Golgi apparatus, free ribosomes or mitochondria in the treated epithelium. It is concluded that this treatment provides an epithelium lacking all features of keratinization and may be a useful model for examining metabolic activities specifically associated with keratinization.

Glycolytic activity of neonatal rat palatal mucosa maintained in organ culture

Abstract The glycolytic activity of neonatal rat palatal mucosa was determined after maintenance in a chemically defined medium for periods up to 28 days. Glycolytic specific activity progressively fell over the culture period but the protein content per expiant progressively increased. When expressed per expiant, the glycolytic activity was increased after 2 days of maintenance in vitro but then slowly returned to control values by 28 days. It is suggested that these changes are the result of altered rates of cell proliferation and maturation rather than a disturbance of cellular metabolism resulting from sub-optimal culture conditions.