Biomedical Engineering Reference
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Fig. 6.4 Muscle-tendon interactions following the formation of the MTJ. ( a ) Formation of the
MTJ. The MTJ ( black ) is formed through
PS muscle-specific integrin association with the
tendon-secreted ECM component thrombospondin (Tsp), and its regulator Slow. Laminin (Lam)
binds the
PS tendon-specific integrin. At this stage HOW(S) is elevated in the cytoplasm of
the tendon cell promoting the formation of StripeA (SrA) essential to induce terminal differentia-
tion by inducing the expression of Shortstop (Shot), Delilah (Dei), and b1tubulin (
1Tub). ( b ) Side
view of two muscles from adjacent segments attached to a single tendon cell. Green and orange
are the tendon-specific and muscle-specific integrin receptors. The ECM proteins Tsp and Laminin
are deposited between the muscles and tendon cells and the ECM protein Tiggrin is deposited
between the two adjacent muscles
The earliest event in the construction of Drosophila MTJ is the tendon-specific
secretion of Tsp, which precedes muscle attachment and the assembly of PS
integrins on the muscle and tendon surfaces. While migrating, the muscle does
not respond to Tsp even when ectopically expressed; however, once the muscle
ends approach the tendon cell, PS2 integrin gradually accumulates at the muscle
ends, presumably as a result of inside-out integrin signaling which, following
association of its cytoplasmic tail with Talin, enhances the affinity of its ectodomain
to Tsp [ 27 , 33 ].
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