Autolysis and heterolysis of the epidermal cells in anuran tadpole tail regression

Abstract

Autolysis and heterolysis of the degenerating epidermis of the tail fin of Rana japonica tadpoles during spontaneous metamorphosis were observed by transmission and scanning electron microscopy. In the early climactic stages of metamorphosis (st. 19-20), the outermost epidermal cells developed vacuoles that were acid phosphatase positive and showed apparent breakdown of the cell membrane. The cells shrunk, perhaps due to the rupture of the cell membrane, and sloughed off without typical cornification. As tail resorption proceeded, autolysis of the epidermal cells spread towards the inner layers, in which some epidermal cells lost desmosomal junctions. They also displayed atrophic figures with condensed cytoplasm, breakdown of the cell membrane, and pycnotic nuclei. Lymphocytes, neutrophils and macrophages were already present in the basal layers of the premetamorphic epidermis (st. 10). Based on ultrastructural observation, blood cells could be distinguished from autolysing epidermal cells. Only a few blood cells were found in the early climactic stages of metamorphosis (st. 19-20), but the number of the blood cells, especially macrophages, greatly increased during the final stages of metamorphosis (st. 23-24). During the final stages, many macrophages were observed to phagocytose the autolysing epidermal cells by projecting slender pseudopodia into the inner epidermis. Macrophages also were observed to pass through the degraded basal lamella. These results suggest that not only autophagy but also heterophagy of the epidermal cells by the macrophages is a major process in the regression of the tail fin epidermis.

Thyroid hormone regulation of apoptotic tissue remodeling during anuran metamorphosis

“…They found that the two major cell types, epidermal and muscle cells, of the tail undergo a series of well defined, sequential morphological changes of apoptosis, including the condensation of the cytoplasm and the nuclear chromatin and the subsequent formation of the apoptotic bodies. Similar findings have also been reported for Rana japonica [6] and Xenopus laevis [7].…”

The thyroid hormone-induced tail resorption program during Xenopus laevis metamorphosis.

“…A possible role for these proteins in tail resorption might be their participation in the recognition by macrophages of cells or matrix fragments that they will engulf (45). Macrophages are reported to play a major role in cleaning up cellular debris during tail resorption (46). Role of Proteinases: Remodeling, Metastasis, and Apoptosis.…”

Tadpole skin dies autonomously in response to thyroid hormone at metamorphosis

“…At the climax of metamorphosis larval skin cells become keratinized (6) and their nuclei become pycnotic (3,4), suggestive of apoptosis. We have used active caspase-3 immunocytology to assay for apoptosis of larval epidermal cells (Figs.…”

“…The premetamorphic dermis consists of the collagen lamella, an adjacent single layer of subepithelial fibroblasts, and melanophores (2). As thyroid hormone (TH) concentration rises in the tadpole during metamorphic climax the outer two cell layers of the epidermis are thought to die by apoptosis (3)(4)(5)(6). The basal cells of the tadpole epidermis are progenitors for the adult frog epidermis (7)(8)(9).…”