The satellite cell bud and myoblast in denervated mammalian muscle fibers

Abstract

AbstractSatellite cells, rarely seen on normal muscle fibers, are located between the sarcolemma and the basement membrane of a muscle fiber. Limb muscles and the extraocular muscles of adult guinea pigs were denervated and studied from two to seven days after operation. Satellite cells are now frequently seen. A nucleus surrounded by a small amount of cytoplasm separates from a denervated muscle fiber and forms a satellite cell. A series of clefts and membranes forms in the periphery of the muscle fiber to make separation channels and pinch off the muscle cell nucleus and its cytoplasm from the parent fiber. This cell, now called a satellite cell bud, can be seen in the process of splitting off from the parent muscle fiber, with portions of the same cell separated from and still part of the muscle fiber. The sacs of endoplasmic reticulum in the satellite cell bud dilate markedly. Centrioles and a cilium form in the satellite cell bud. The bud elongates, and concentrations of ribosomes and polyribosomes appear in its cytoplasm. Small points of contact, with membrane thickenings, between bud and parent fiber allow the elongating bud to be kept longitudinally oriented under the basement membrane of its parent fiber. Muscle filaments form in the elongating bud, which is now a myoblast. Hence, satellite cells arise from portions of denervated muscle fibers themselves, elongate, and become myoblasts.