Observations on the histochemistry and ultrastructure of regenerating caudal epidermis of the @entity38187 XXXX (Sphenodontida, Lepidosauria, Reptilia).

@entity4890 @entity4576 @entity7944 @entity38353 @entity38187
Study of the histology, histochemistry, and fine structure of caudal epidermal regeneration in @entity38187 through restoration of a scaled form reveals that the processes involved resemble those known in lizards. Following establishment of a @entity7944 ( @entity7944 ), subjacent scale neogenesis involves epidermal downgrowths into the dermis. Although the process is extremely slow, and most new scales do not overlap, their epidermal coverings reestablish epidermal generation (EG) formation. As in lizards, the flat, alpha-keratogenic, @entity7944 cells contain lipids as revealed by their affinity for @entity38353 . A few mucous cells that store large PAS-positive mucus-like granules also occur in @entity7944 . During differentiation of @entity7944 cells, among the bundles of 70-nm tonofilaments are many lamellar bodies (LBs) and mucous granules (MGs) that discharge their contents into the cytoplasm and extracellular spaces producing a strongly PAS-positive keratinized tissue. @entity4890 with mucus is a primitive characteristic for amniote vertebrates, probably related to functions as a barrier to cutaneous water loss (CWL). As scale neogenesis begins, beneath the superficial @entity7944 appear 3-5 layers of irregularly shaped cells. These contain tonofilament bundles surrounded by small, round keratohyalin-like granules (KHLGs) and a keratinized matrix with beta-keratin packets and a 3-5-nm thick keratin granulation. This mixture of alpha- and beta-keratogenic capacities resembles that seen in the innermost cells of a normal @entity38187 epidermal generation. As in the latter, but in contrast to both normal and regenerating lizard epidermis, no definable shedding complex with interdigitating clear layer and oberhautchen cells occurs (Alibardi and Maderson, 2003). The tortuous boundaries, and merging beta-keratin packets, identify subjacent keratinizing cells as precursors of the typical stratified, squamous beta-layer seen in long-term regenerated caudal skin wherein the entire vertical sequence of epidermal layers resembles that of normal scales. The sequence of events in caudal epidermal regeneration in @entity4576 resembles that documented for lizards. Observed differences between posttrauma scale neogenesis and scale embryogenesis are responses to functional problems involved in, respectively, restoring, or forming, a barrier to CWL while accommodating rapid somatic growth.
