Three-dimensional appearance of bovine epidermal keratinocytes in different stages of differentiation revealed by cell maceration and scanning electron microscopic investigation

The epidermis of the modified skin of the bovine hoof is a highly mechanical loaded tissue. Consequently, all cell connections have to withstand high mechanical forces. As an adaptation to this stress, the epidermal keratinocytes show characteristic surface modifications. Furthermore, the tissue displays a complex three-dimensional architecture which is difficult to appreciate from histological sections. SEM-observation of macerated tissue samples is a fast, easy to use and reliable tool to receive three-dimensional information about the appearance and spatial relationship of cells within a tissue. Using cell maceration, the aim of this study was to separate individual as well as smaller groups of keratinocytes in order to reveal the formations of the cell surface, the appearance of individual cells and the spatial relationship of cells within the tissue. A NaOH maceration method described in literature was modified and applied to tissue samples from the wall and bulbar segment of the hooves of six cows. This method facilitated separation between the epidermal cells. Single cells as well as cell groups were available for SEM observation which revealed a three dimensional appearance characteristic for different stages of differentiation of the keratinocytes. The observed findings suggest that throughout the process of differentiation the surface modifications provide the basis for a stable cell to cell adhesion which is established by desmosomes and the intercellular cementing substance. Additionally, the broadened cellular surface area is related to the supply of the highly metabolic active living epidermal cells with nutrients and oxygen. Longer cell processes typically found in the central surface area of the keratinocytes may carry gap junctions and may be involved in cell communication. This, however, has to be clarified by further electron microscopic studies. The demonstrated appearance of individual cells and the complex architecture enable the hoof epidermis to fulfil its unique biomechanical functions.