Fig. 3

Hypothesized mechanisms for JFs formation. A Exocytosis model modified from the previous hypothesis. E18.5-P0, beneath the depression areas, numerous caveolae with coated or uncoated were found. As these caveolae fused to the post-membrane opposed sites to the active zone, incipient JFs emerged on the stage. Accompanying more new membranes were inserted at P7-P28, the post-synaptic membrane investigated deeper into the cytoplasm and formed the maturely JFs [10]. However, this hypothesis can not explain how the BL are inserted into the JFs (question mark), especially why the secondly JFs formation. B The diaphragm of mice at P1 was observed by transmission electron microscope. Although Schwann cells (green) encapsulate multiple axons (red) in a single NMJ, only a single JF was observed beneath the NMJ. The incipient JF showed apparent invagination features, and the BL (arrow) within the JF maintained continuity with the outside. The inset figure is an enlarged view. Note that the active zone (arrowhead) is not opposed to the JF. C Invagination model was proposed by this reviewer. At E18-P0, the AZs were preceded by the formation of JFs, and they were not aligned with the JFs [13]. Initiated single from the axon terminal induced cytoskeleton pulled the sarcolemma investigated into the cytoplasm. In the first week after birth, the incipient JFs aligned the active zone to the opposed site with the interaction with BL, and the VGSC integrated into the valley of JFs. In the first 4 weeks after birth, the second JFs formed, which keep this mature structure to the adult stage. S: Schwann cell, M: Muscle fiber, A: Axon. The scale bar in B is 500 nm