Title: T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases | Skeletal Muscle | Full Text
Headings: T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases
T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases
Abstract
Introduction
T-tubule plasticity
Morphological aspects of triad biogenesis
Sarcoplasmic reticulum
Transverse tubule
Molecular mechanisms involved in T-tubule biogenesis and triad formation and maintenance
Table 1 Proteins implicated in triad organization, roles and associated human diseasesa
Caveolin 3
Amphiphysin 2 (BIN1)
Dysferlin
Mitsugumins
Junctophilins
Myotubularin
The RyR-DHPR complex
Conclusion
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Content: The molecular determinants implicated in the functional and structural organization of the SR have been reviewed elsewhere [ 16 ]. The chronology of SR biogenesis was well investigated using electron microscopy (EM) during muscle differentiation in mouse [ 17 ]. These observations were also supported by studies employing chicken embryo [ 18 ]. In mouse, the SR is detected from as early as embryonic day 14 (E14) with punctate RyR clusters that are located in the periphery of the myofiber [ 17 ]. At this stage, the content of the feet (RyR) in the junctional SR is poor, and some SR elements without any feet are observed. At E16, RyR containing elements become abundant and start to be associated with the edges of A bands (A-I junctions) of the newly formed sarcomeres. This association results in a distinct banding pattern of a discrete SR network at the I-band with thin longitudinal connecting SR elements [ 17 ]. During the next days (E17 and E18), junctional SR acquires a predominant transverse distribution taking their final position by forming triad rows at each side of the Z-line (two SR sacs connecting one T-tubule in each triad) [ 17 ]. During the maturation of SR membranes, the frequency of feet increases, in particular, between E16 and E18, when all junctions become filled by feet. The width of the junctional gap is between 9 and 12 nm.