Fine structural observations on cell death in the epidermis of the external gills of the larval frog, Rana pipiens

Abstract

The fine structure of the epidermis of the external gills of the larval frog, Rana pipiens, was observed during the period of gill degeneration. Many of the epidermal cells underwent morbid alterations. In typical degenerating epidermal cells the nucleus became irregular in outline, chromatin formed electron-dense clumps and the nuclear envelope increased in width. Lysosomes became prevalent in the cytoplasm of these cells and progressively larger autophagic vacuoles appeared. As degeneration continued, apical epidermal cells were found embedded deeper within the epidermis. In some instances cell processes from two neighboring epidermal cells extended partially around the relocated degenerating apical epidermal cells probably contributing to their translocation; phagocytosis was completed by a single cell in other instances. The degree of participation of the phagocytic epidermal cells in the degenerative process was uncertain. The distribution of acid phosphatase activity was followed in specimens treated by the Gomori technique. Profiles of cisterna-like elements, positive for the enzyme, suggested that perhaps entire Golgi cisternae contributed to the formation of autophagic vacuoles in combination with small vesicles. Heterophils and macrophages observed in the degenerating gills were believed to participate in the removal of the dying cells.The development and degeneration of external gills of both anurans and urodeles were studied by several nineteenth century investigators (Whitney, 1867; Boas, 1882;Maurer, 1888;Naue, 1890; Clemens, 1895). Experimental embryologists of the early twentieth century found amphibian external gills useful organs for studying the interactions between the germ layers of embryos (Ekman, '13; Harrison, '21; Severinghaus, '30; Moser, '40). Physiologists have explored the relationship between the concentration of respiratory gases and the growth of external gills (Drastich, '25; Savage, '61; Boell et al., '63; Lprvtrup and Pigon, '68). However, cellular changes occurring during degeneration of the external gills of anurans have never been reported.The external gills of the larval frog, Rana pipiens, and many other species of anurans are transitory respiratory organs that arise from the third, fourth and fifth visceral arches, just prior to the heart-AM. J. ANAT., 132: 301-318.beat stage. The finger-like external gill filaments consist of an epidermis of two cell layers, connective tissue containing collagenous fibers and scattered mesenchymal cells, and one or more large capillary loops. The gills grow to a maximum length of about 1 mm. After only two or three days of function, the opercular fold begins to enclose them in the opercular chamber. Concurrently, the external gills start to degenerate resulting in their disappearance within five to seven days. The external gills are replaced by internal gills, that presumably take over the respiratory function (Rugh, '51).The external gills of the larval frog are an excellent system for investigation of developmental cell death ...

Developmental cell death: morphological diversity and multiple mechanisms

“…In fact, in most cases of cell death during ontogenesis, unbound cytoplasmic acid phosphatase activity is either not found in histochemical preparations (Scheib 1965b;Salzgeber and Weber 1966;Scharrer 1966) or is found only in a few cells at very advanced stages of cell death (Michaels et al 1971 ;Pannese et al 1976). In dying neurons during development, the stability of lysosomal membranes has also been shown by their failure to release horseradish peroxidase (Hornung et al 1989) or radioactively labeled fragments of DNA (Clarke and Hornung 1989).…”

The ultrastructure of oral (buccopharyngeal) membrane formation and rupture in the anuran embryo

“…On the other hand, phagocytosis by epithelial cells has been observed in external gills of larval frog (Michaels et al, 1971), in mouse oral mucosa during palate fusion (Farbman, 1968), in insect epidermis at meta- (Goldsmith, 1966), and in some epithelia (Schliitter, 1973;Olson and Everett, 1975;Kelley and Fallon, 1976;Garcia-Porrero et al, 1978, 1979, 1984. It is quite difficult to differentiate between a normal epithelial cell undergoing autolysis and one possessing phagocytic materials.…”

“…The cell death in epithelia involving lyso-soma1 participation and autolysis has been reported in many papers: for example, in external gills of larval frog (Michaels et al, 19711, in the chick (Salzgeber and Weber, 1966;Haffen and Salzgeber, 19771, insect salivary regression (Jurand and Pavan, 19751, in the uterus during implantation of mouse blastocyst (El-Shershaby and Hinchliffe, 19751, and Mullerian duct regression in chick embryos (Scheib, 1977). On the other hand, phagocytosis by epithelial cells has been observed in external gills of larval frog (Michaels et al, 1971), in mouse oral mucosa during palate fusion (Farbman, 1968), in insect epidermis at meta- (Goldsmith, 1966), and in some epithelia (Schliitter, 1973;Olson and Everett, 1975;Kelley and Fallon, 1976;Garcia-Porrero et al, 1978, 1979, 1984. It is quite difficult to differentiate between a normal epithelial cell undergoing autolysis and one possessing phagocytic materials.…”

Ultrastructure and development of the gills in Rana dalmatina (Amphibia, Anura)

“…The latter have a very rapid development and just as rapidly they come against the phenomenon of regression (Michaels et al 1971) which in the space of a very few days concerns the entire gill apparatus. The examination by light microscope has confirmed a structural arrangement completely analogous to that observed in the gills of Urodela and it has been possible to recognize a connective support, in this case richly vascularized, above which the epithelial cell layers are placed.…”