Microscopic and ultrastructural observations on the regenerating scales of the lizard Podarcis muralis clarify the origin of the micro-ornamentation

The present study conducted using immunofluorescence, scanning electron microscopy, and transmission electron microscopy aims to determine the origin of the lamellated pattern and of the micro-ornamentation formed in tail scales of the lacertid lizard Podarcis muralis. Regenerating scales shows the typical formation of all the epidermal layers of lizard epidermis, including clear and Oberhautchen layers. The latter initiates the accumulation of hard corneous material containing corneous beta proteins (CBPs) that determine a tension with the overlaying softer clear layer containing mainly intermediate filaments of keratins (IFKs). The two layers, initially joined by numerous desmosomes, are later displaced one from the other with the growth of regenerating scales, forming a slanted surface as observed under transmission electron microscopy (TEM). At the beginning of scale regeneration, the slanted tips form an irregular lamellated pattern on the surface of Oberhautchen cells, appearing as crests or waves under scanning electron microscopy (SEM). In the following scale differentiation, growth, and shedding of molt, the irregular crests form a more ordered and parallel microsculptured and micro-ornamentation pattern when Oberhautchen and beta-cells merge one to another and give rise to a mature beta-layer. Hard CBP-based corneous material and electron-dense materials of unknown composition together with IFKs are accumulated in the slanted surface of the differentiating Oberhautchen cells. During scale growth, the Oberhautchen surface matures into a jig-saw outline that gives rise to the lamellated pattern of mature micro-ornamentation. The study suggests that complex micro-ornamentation patterns in other lizard species can also vary during scale formation, in development, growth, or regeneration.