Morphology of ventral epidermis of Rana catesbeiana during metamorphosis

Abstract

A detailed morphological examination of the bullfrog tadpole ventral epidermis and changes in structure that occur during metamorphosis has not been done. Knowledge of this is crucial to interpretation of physiological studies such as those dealing with development of transepithelial Na+ transport. Examination of tadpole epidermis with light microscopy reveals the presence of three different cell types: apical, basal, and skein. This epidermal morphology is constant until Taylor and Kollros (Anat. Rec. 94:7-23, 1946) stage 19 when degeneration of apical cells is noted. Stages 20 and 21 are characterized by rapid proliferation of basal cells and development of a true stratum germinativum together with the disappearance of other tadpole cell types. By stage 22, epidermal morphology is similar to that of the adult frog. Studies with the electron microscope reveal that as the proliferation proceeds during metamorphosis, the skein cells, at stage 20, differentiate to form the apical border of the skin. The development of the adult frog cell phenotype appears to mimic the cellular differentiation that occurs in the adult epidermis with the cells first developing into progranular cells in the intermediate stratum of the skin and then progressing to granular cells in the outermost living cell layer. The granular cells then undergo cornification to form the stratum corneum. Mitochondria rich cells are not seen in the developing epidermis until stage 21. These observations, when considered with previous results from Na+ transport studies (Hillyard et al.: Biochim. Biophys. Acta 692:455-461, 1982), suggest that both the physiological differentiation and morphological differentiation are simultaneous events.

Glycoconjugate localization in larval and adult skin of the bullfrog, Rana catesbeiana: A lectin histochemical study

“…The histological characteristics of larval and adult Rana catesbeiana skin have been well established (e.g., Robinson and Heintzelman, 1987;Yoshizato, 1989Yoshizato, , 1996Izutsu et al, 1993). However, other than our preliminary reports in which lectins were used as histochemical probes (Kaltenbach et al, 1991;Kaltenbach and Faszewski, 2002), we have found no reference to the localization of glycoconjugates in the skin of this semiaquatic species.…”

Tadpole skin dies autonomously in response to thyroid hormone at metamorphosis

“…At metamorphosis the subepithelial fibroblasts secrete proteolytic enzymes such as collagenase-3 and invade the collagen lamella, the dermis thickens, and adult skin glands form (2,10). A major difference between the tadpole and frog skin is that all cells in the tadpole epidermis replicate whereas only the basal cells replicate in frog skin (11). This latter ''germinative'' replication is characteristic of the epidermis of all adult vertebrate species whereas the self-replicating tadpole epidermis resembles the mammalian fetal skin called the periderm (12).…”

Different sensitivity to amiloride of body and tail skins of Rana catesbeiana tadpoles during metamorphosis

“…The types and relative numbers of specific cells differ between body and tail skin and change during stages XX-XXV (Robinson and Heintzelman 1987;Nishikawa et al 1989). Body skin at stage XX is composed of three types of larval epidermal cell; apical, skein and basal cells.…”

“…Therefore, the characteristics of body and tail skin appear to be different. Robinson and Heintzelman (1987) reported that the ratio of types of epidermal cell differs between body skin and tail skin. Accordingly, it can be expected that the system for active Na + transport also differentiates differently between the body and tail skins.…”