Immunolocalization of keratin-associated beta-proteins (beta-keratins) in the regenerating lizard epidermis indicates a new process for the differentiation of the epidermis in lepidosaurians

The process of keratinocyte differentiation was analyzed in the regenerating epidermis of the lizard Anolis carolinensis, where the genes coding for beta-proteins (beta-keratins) are known. The regenerating epidermis forms all epidermal layers found in normal scales (Oberhäutchen-, beta-, mesos-, and alpha-layer). Three specific proteins representing the larger families of beta-proteins, glycine-rich (HgG5, 28% glycine, 3.6% cysteine), glycine-cysteine medium-rich (HgGC10, 13% glycine, 14.5% cysteine), and glycine-cysteine rich (HgGC3, 30.4% glycine, 8.7% cysteine) have been immunolocalized at the ultrastructural level. HgG5 is only present in differentiating beta-cells, a weak or no labeling is observed in Oberhäutchen and is absent in alpha-cells. The protein is located in the pale corneous material forming the compact beta-layer but is absent in mature Oberhäutchen cells. HgGC10 is present among beta-packets in Oberhäutchen and beta-cells but disappears in more compact and electron-pale corneous material. The labeling disappears in mesos-cells and is present with variable intensity in alpha-cells, whereas lacunar and clear-cells are low labeled to unlabeled. HgGC3 is sparse or absent in beta-cells but is lightly present in the darker corneous material of differentiating and mature alpha-cells, lacunar-cells, and clear-cells. The study suggests that while glycine-rich proteins (electron-pale) are specifically used for building the resistant and hydrophobic beta-layer, cysteine-glycine rich proteins (electron-denser) are used to form the pliable corneous material present in the Oberhäutchen and alpha-cells. The differential accumulation of beta-proteins on the alpha-keratin cytoskeleton scaffold and not the alternance of beta- with alpha-keratins allow the differentiation of different epidermal layers.