Muscle cell death during the development of head and neck muscles in the chick embryo

Abstract

Degenerating myofibers have been reported in the embryos and neonates of a number of birds and mammals, but neither the pervasiveness of the phenomenon nor the spatiotemporal patterns of degeneration has been examined in detail. Using transmission electron microscopy, we determined the patterns of muscle cell death in the chick biventer cervicis, a head extensor muscle. Cell death is most pronounced at incubation days 10 through 15, and occurs throughout the muscle. This is the period during which many myofiber clusters segregate into individual fibers, each with a separate basal lamina, and secondary myofibers become demarcated. Cells of largest diameter, presumably the primary myofibers, are preferentially affected. Degenerating cells exhibit a cohort of cytological features consistent with apoptosis, including the presence of dense, darkly-staining, hypercontracted myofibrils, misshapen nuclei with irregular chromatin condensations along the nuclear envelope, and scores of cytoplasmic vesicles and vacuoles. In cross section some large diameter muscle cells are characterized by sparse, flocculent cytoplasm that is devoid of myofibrils and organelles. Some show disintegrating cell membranes. In longitudinal section 200-300 pm long regions of hypercontracted myofibrils alternate with areas devoid of fibrils; this arrangement suggests that the myofibrils break into segments that are in register along one part of a muscle fiber and entirely absent from the adjacent length of fiber. We have observed similar patterns of muscle cell degeneration in the complexus, splenius cervicis, depressor mandibulae, and branchiomandibularis muscles. By day 18 of incubation most signs of degeneration are absent and by hatching (day 21) the muscle fibers all appear healthy. Many of these cytological changes in embryonic head muscle cells are characteristic of programmed cell death. We hypothesize that large-scale death of myocytes is a normal part of avian myogenesis and an important mechanism for affecting the transformation from embryonic to hatching muscle patterning. o 1995 Wiley-Liss, Inc.

Expression of tissue transglutaminase in the developing chicken limb is associated both with apoptosis and endochondral ossification

“…54 Apoptotic muscle cells have been described during skeletal muscle development. 55 We observed apoptotic myoblasts during early development of striated muscle characterized by migration and fusion of the myoblasts to form myotubes. In the day 7.5 embryonic limb apoptotic myoblasts were scattered in developing leg and thigh skeletal muscle.…”

Positive regulation of skeletal myogenesis by R-Ras

“…Though we cannot substantiate, for certain, the role of R-Ras in myogenesis in vivo at the present stage, one can assume that R-Ras may prevent cell death and stimulate locomotion on muscle dierentiation during embryogenesis and tissue regeneration. It has been reported that myogenesis is accompanied by cell death of myoblasts in vivo (McClearn et al, 1995). R-Ras thus may maintain survival of muscle precursor cells, which are more sensitive to apoptosis than terminally dierentiated myotubes, during myogenesis.…”

Developmental characteristics of pectoralis muscle in Pekin duck embryos

“…Chen et al (2006) found morphological changes of the skeletal muscle, tendon, and periosteum in senescence-accelerated mice (SAMP6) compared to age-matched normal SAMR1 mice. McClearn et al (1995) explored the pervasiveness of myofiber degeneration and spatiotemporal patterns of degeneration during the development of head and neck muscles in chick embryos by evaluating morphological characteristics of muscle cells. In duck, Li et al (2010) compared morphological characteristics of pectoral and leg muscle tissues during duck embryo stages to the neonatal stage through paraffin sections.…”