Differentiation of the epidermis of neck, tail and limbs in the embryo of the turtle Emydura macquarii (Gray, 1830)

The development of the skin in turtles and the differentiation of the first keratinized layers are largely unknown processes. The histology and ultrastructure of the developing skin of neck, tail and limbs of the embryo of the turtle Emydura macquarii were studied. This study showed that three to four embryonic layers are initially formed from the basal layer. They contain scarce bundles of 8-12 nm-thick intermediate filaments of keratin, and many coarse 28-35 nm-thick filaments of unknown nature. The coarse filaments form reticulate bodies similar to those of lepidosaurian reptiles and birds, and form large aggregations within corneocytes of the embryonic epidermis. Embryonic layers also contain mucus and vesicular bodies, the latter associated with lipid droplets. Lipids and mucus are partly discharged into the amniotic fluid. Shortly before hatching, typical alpha-keratinocytes, containing keratin filaments and no coarse filaments, replace the embryonic epidermis. Mucus and lipids are, however, retained among alpha-keratinocytes after hatching. The loose dermis of early embryonic stages rapidly turns into a dense connective tissue that strengthens the delicate epidermis. Large collagen fibrils contact the basement membrane of the epidermis of the tail. Lipidic material is also stored in dermal fibroblasts.