Biogenesis of transverse tubules: immunocytochemical localization of a transverse tubular protein (TS28) and a sarcolemmal protein (SL50) in rabbit skeletal muscle developing in situ

To study the biogenesis of transverse tubules, the temporal appearance and distribution of TS28 (a specific marker of transverse tubules absent from the sarcolemma in adult skeletal muscle; 28,000 Mr) and SL50 (specifically associated with the sarcolemma and absent from the region of the transverse tubules in adult rabbit skeletal muscle) (Jorgensen, A.O., W. Arnold, A. C.-Y. Shen, S. Yuan, M. Gaver, and K.P. Campbell. 1990. J. Cell Biol. 110:1173-1185) were determined in rabbit skeletal muscle developing in situ (day 17 of gestation to day 15 newborn) by indirect immunofluorescence labeling. The results presented show that the temporal appearance and subcellular distribution of TS28 is distinct from that of SL50 at the developmental stages examined. TS28 was first detected in some, but not all, multinucleated myotubes on day 17 of gestation. At this stage of development, SL50 and the Ca2(+)-ATPase of the sarcoplasmic reticulum were already present in all myotubes. TS28 first appeared in discrete foci mostly confined to the cell periphery of the myotubes. At subsequent stages of development (days 19-24 of gestation), TS28 was also found in shoft finger-like structures extending obliquely and transversely from the cell periphery towards the center of the myotubes. 1-2 d after birth, TS28 was observed in an anastomosing network composed of transversely oriented chickenwire-like networks extending throughout the cytoplasm and interconnected by longitudinally oriented fiber-like structures. As development proceeded, the transversely oriented network became increasingly dominant. By day 10 of postnatal development, the longitudinally oriented component of the tubular network was not regularly observed. At none of the developmental stages examined was TS28 observed to be uniformly distributed at the cell periphery. SL50, like TS28, first appeared in discrete foci at the cell periphery. However, shortly after its first appearance it appeared to be distributed along the entire cell periphery. Although the intensity of SL50 labeling increased with development, it remained confined to the sarcolemma and was absent from the interior regions of the myofibers, where transverse tubules were present at all subsequent developmental stages examined. Immunoblotting of cell extracts from skeletal muscle tissue at various stages of development showed that SL50 was first detected on day 24 of gestation, while TS28 was not detected until days 1-2 after birth. Comparison of these results with previous ultrastructural studies of the formation of transverse tubules supports the idea that the temporal appearance and subcellular distribution of TS28 correspond very closely to that of the distribution of forming transverse tubules in rabbit skeletal muscle developing in situ.(ABSTRACT TRUNCATED AT 400 WORDS)