Scanning electron microscopy of macrophages in the tail musculature of the metamorphosing anuran tadpole, Rana japonica

Abstract

Scanning electron microscopy was used to investigate the morphological changes of the tail musculature of the metamorphosing anuran tadpole, attention being focused on phagocytosis by macrophages. Muscle fibers were stained en bloc with silver and freeze-fractured during dehydration, or torn after drying. Samples were sputter-coated with gold-palladium and observed in both secondary electron- and back-scattered electron modes with a scanning electron microscope. Various cells were identified by the methods of secondary electron- and back-scattered electron images. Some macrophages lying between muscle fibers at prometamorphic stages possessed numerous finger-like projections and well-developed ruffles. During degeneration of muscle fibers macrophages collected in the degenerating region and invaded the space between the disordering myofibrils. In advanced stages the numbers of macrophages clearly increased on or around the degenerating muscle fibers. At the climactic stage fragmented muscles were entrapped and then engulfed by the macrophages. With the completion of phagocytosis, the macrophages became globular with reduction of the ridge-like ruffles. Macrophages may play a role not only in scavenging the fragmented muscle fibers, but also using their long processes in active formation of the fragments.

Cytochemical studies of hydrogen peroxide production in the tadpole tail ofRana japonica during metamorphic climax

“…One of the most dramatic morphological changes in anuran tadpoles during metamorphosis is the diSappearance of their tail, which consists of skeletal muscle, notochord, blood vessels, nerve fibre and skin (Weber, 1964;Niizima et al, 1964;Watanabe & Sasaki, 19.74;Fox, 1975;Sasaki & Watanabe, 1983;Sasaki et ~I., 1983Sasaki et ~I., , 1985Kinoshita et al, 1985Kinoshita et al, , 1986Watanabe et al, 1985). We have reported recently that during the degeneration of tail muscle fibres macrophages were collected at the sites of degeneration.…”

“…We have reported recently that during the degeneration of tail muscle fibres macrophages were collected at the sites of degeneration. The surface of muscle fibres are attached by finger-like projections of macrophages and during degeneration the spaces between disordering myofibrils are invaded by finger-like projections of macrophages (Watanabe et al, 1985). Such macrophages with their long processes may play a role not only in scavenging the cell debris, but in fragmenting the cells initially (Watanabe & Sasaki, 1974;Watanabe et al, 1985).…”

“…During the degeneration of tail muscles, hydrogen peroxide production may result in dissolution or destruction of the muscle fibre membranes thereby allowing penetration by the macrophage (Watanabe & Sasaki, 1974;Watanabe et al, 1985). However, no studies on the plasma membrane of macrophages in metamorphosing tadpole tails have been reported previously, In the present study we have investigated the occurrence of hydrogen peroxide in the tail of Rana japonica larvae during metamorphosis by means of a modified cerium-method (Ohno et al, 1982a), originally prescribed by Briggs et al (1975).…”

“…The surface of muscle fibres are attached by finger-like projections of macrophages and during degeneration the spaces between disordering myofibrils are invaded by finger-like projections of macrophages (Watanabe et al, 1985). Such macrophages with their long processes may play a role not only in scavenging the cell debris, but in fragmenting the cells initially (Watanabe & Sasaki, 1974;Watanabe et al, 1985). Human polymorphonuclear leucocytes (PMN) (Ohno et al, 1982a,b) and guineapig macrophages (Moriguchi & Hirai, 1985) stimulated to phagocytosis were reported to exhibit extensive deposits indicative of H202 production.…”

Apoptosis of larval cells during amphibian metamorphosis

“…There still remains a historical controversy as to the origin of macrophages which increase rapidly in number within the degenerating larval tissue. One explanation has been that mesenchymal cells transform into macrophages (Fox and Whitear, 1990;Watanabe et al, 1985;Weber, 1964), whereas the other stipulates that macrophages differentiate from monocytes in blood capillaries (Lehman, 1953). Recently, it has been shown in intestinal fragments isolated from Xenopus tadpoles and cultured organotypically that macrophages rapidly increase in number and phagocytose apoptotic bodies of larval cells as in spontaneous metamorphosis.…”