The structure and histochemistry of proteinaceous constituents in cellular components of various layers of the epidermis of the chequered water snake, Natrix piscator, throughout the sloughing cycle have been described.
Histologically, six consecutive stages are recognized during one complete sloughing cycle. In Stage I, immediately following sloughing, the epidermis consists of an inner stratum germinativum, one or two layers of undifferentiated epidermal cells and the new outer epidermal generation represented by the Oberhautchen, β-layer, mesos layer and an α-layer which continues to differentiate and mature throughout Stage 1 and is observed even in Stage 2. The presence of several layers of undifferentiated epidermal cells over the stratum germinativum, a characteristic feature of Stage 2, results from the temporary slowing of their differentiation into the cells of various epidermal layers. Stage 3 includes differentiated lacunar tissue and the clear layer of the outer epidermal generation, and the presumptive Oberhautchen and β-layer of the inner epidermal generation. In addition to marked cytological and histochemical changes in the lacunar tissue and the maturation of various keratinized layers. Stages 4 and 5 include the presumptive mesos and α-layers, respectively. Stage 6 is characterized by total disintegration of the lacunar tissue and maturation of various keratinized layers, except the presumptive α-layer, of the inner epidermal generation, which is still incomplete. The degeneration of the lacunar tissue is discussed in relation to the cessation of the supply of nutrients and other body fluids from underlying epidermal cells.
Histochemically, the Oberhautchen resembles the mesos and α-layers in being strongly positive for -SH and -NH2 groups, bound calcium and basic proteins. However, it shows more similarity with the α-layer in its moderate reaction for tyrosine and tryptophan, which is more intense in the mesos layer; and shows more similarity with the mesos layer with its very strong reactions for -SS groups, unlike the α-layer which remains unstained.
The functional value of tyrosine- and tryptophan-rich proteins in the keratinized layers of the epidermis is not immediately apparent.
In addition to the high content of-SS groups, providing durability and mechanical strength, and protein-bound calcium, adding hardness, the vertical striations in the Oberhautchen of the scales probably reinforce the epidermal superficial layer to guard against wear and tear by abrasion.