Cell-to-cell communication and myogenesis.

Abstract

Cell-to-cell communication was characterized in prefusion chick embryo myoblast cultures, and it was determined that the prefusion myoblasts can interact via gap junctions, ionic coupling, and metabolic coupling. The biological relevance of this communication was supported by the detection of gap junctions between myoblasts in embryonic muscle. Communication was also examined in fusionarrested cultures to determine its potential relationship to fusion competency. In cultures that were fusion arrested by treatment with either 1.8 mM ethyleneglycolbis-(fl-aminoethyl ether)N,N'-tetraacetic acid (EGTA), 3.3 x 10 -6 M 5-bromodeoxyuridine (BUdR), or 1 /~g/ml cycloheximide (CHX), both gap junctions and ionic coupling were present. Therefore, it is possible to conclude that cell communication is not a sufficient property by itself, to generate fusion between myoblasts. The potential role of communication in myogenesis is discussed with respect to these observations. KEY WORDS cell-to-cell communication junctions 9 ionic coupling metabolic coupling myoblast fusion myogenesis gapThe differentiation of skeletal muscle in vivo and in vitro (in culture) is accompanied by the fusion of mononucleated muscle cells (myoblasts) into multinucleated mature muscle fibers (58). This fusion event, in culture, is preceded by a period of cell multiplication and cellular interaction. During this time, the cells are closely apposed and aligned in multicellular strings; this stage of differentiation has been referred to as the "prefusion lag period" (61). Under standard culture conditions this lag period is quite constant, and only cells which have completed their prefusion changes participate in the formation of muitinucleated fibers (59). The fusion process that follows the lag period has been previously regarded as a critical event in myogenesis. However, at present, it appears that it is just one of the important events that contribute to the formation of a differentiated muscle fiber (1, 12. 16, 19, 26, 31, 34, 36, 41, 54, 55, 56, 57, 62). The actual fusion process requires a direct physical interaction of the plasma membranes from adjacent cells, and this had led to a series of investigations of the cell surface elements that may be involved in regulating fusion (5,14,20). Other studies have suggested that fusion is not necessarily regulated by cell surface components; it may, in fact, be under the direct control of intracellular elements (62). Recently, it has been reported that a specific type of cell contact, the gap junction (30), and low-resistance pathways (6) are present between muscle cells during amphibian myotome development in vivo. In both studies, it was suggested that gap junctional communication between the muscle cells is related to the efficient transfer of excitatory stimuli from somite to somite, and not to cell fusion. Data from studies on embryonic rat and chick skeletal muscle cells in culture indicate the possible existence of ionic coupling (measured indirectly) and gap junctionlike structures betwee...

Functional interaction between TRPC1 channel and connexin-43 protein: a novel pathway underlying S1P action on skeletal myogenesis

“…In the present study, we contributed to shed some light on this issue, by showing that TRPC1 channel activity is required for the up-regulation of Cx43 expression elicited by S1P in skeletal myoblasts. The physiological significance of this interaction in skeletal myogenesis is consistent with the well-known role of Cx43 in synchronizing cell differentiation among contacting myoblasts [6,25,48], and in making them competent for syncytial fusion [6,25,49,50]. In particular, we have shown that the functional link between TRPC1 and Cx43 protein in S1P-differentiating myoblasts involves the activation of m-calpain/classical PKCs axis, thus contributing to extend our knowledge on the molecular mechanisms by which S1P exerts its pro-myogenic action.…”

Reorganization of membrane cholesterol during membrane fusion in myogenesis in vitro: A study using the filipin-cholesterol complex.

“…There are various reports of ultrastructural alterations during myogenesis that have been described from thin section (8,13,14,17,22,29) and freeze-fracture (8,14,23) electron microscopies. Our results show that apposed myoblast membranes fuse at several points and that their cytoplasms are continuous through pores that exist between the long vesicles seen in thin section preparations.…”

“…Ultrastructural studies of developing skeletal muscle have provided the basis for the current interest in localized membrane events that are associated with myoblast fusion (8,13,14,17,22,29). An initial event in the overt development of muscle tissue in culture is the fusion of the plasma membranes of neighboring mononucleated myoblasts to form multinucleated myotuves.…”

Differences in the histogenesis of EDL and diaphragm in rat

“…In the differentiation of segmental myotomes, unsegmented mesodermal cells communicate with each other, then separate during morphogenetic movements (Hayes, 1975;Blackshaw and Warner, 1976). Myoblasts at pre-fusion stages are also capable of forming gap junctions, if given the opportunity for close association in vitro (Chow and Young, 1987;Kalderon et al, 1977). At later stages myotubes containing fully differentiated myofibrils are again connected, but become fully distinct functional units in coincidence with innervation and in a manner dependent on activity (Keeter et al, 1975;Dennis, 1981;Dennis et al, 1981;Armstrong et al, 1983).…”

“…Even though some association was found between gap junction presence and cell fusion (Rash and Staehelin, 1974;Rash an Fambrough, 19731, it is clear that in most cases the two are not causally related (Kalderon et al, 1977;KaYderon andGilula, 1979, see Cavaney, 1985).…”