Formation of sarcomeres in the embryonic heart of the lobster.
Cardiomyoblasts in the myocardium of embryonic lobsters at 3-4 weeks and 6 months of development were examined with the transmission electron microscope in order to describe the events in the formation of sarcomeres in a neurogenic cardiac system. Thick and thin myofilaments appear first in the cell periphery near the sarcolemma. They align in parallel in a sequential fashion to form consecutive sarcomeric units. Well-defined A and I bands appear before any semblance of a Z line is present. The initial sarcomere is anchored to the sarcolemma by the insertion of thin myofilaments into a region of electron dense material associated intimately with the sarcolemma. Myofibrils grow outward in several planes away from the electron-dense regions of membrane that serve as focal points for myofibril formation.
D000818:Animals; D002454:Cell Differentiation; D006321:Heart / Q000196:embryology*; D009206:Myocardium / Q000648:ultrastructure; D009210:Myofibrils / Q000648:ultrastructure*; D008121:Nephropidae / Q000196:embryology*; D012508:Sarcolemma / Q000648:ultrastructure