Fig 11. A proposed model for the formation of cargoes.

A) Shown in the cytoplasm is the place of birth of granules that derive from stalled polyribosomes, in a close compacted structure. Alternatively (shown by an interrogation mark), polyribosomes might interact with yet unknown repressors (non coding RNA or proteins) to form granules that are transported to dendrites along microtubules, using motor proteins. Also, shown is a ZBP1-associated repressed RNP emerging from the nucleus. On their way, granules merge to form large cargoes. B) As large cargoes are too voluminous to cross the spine neck, individual small granules, in this instance the ZBP1-RNP devoid of ribosomes, emerge from cargoes and penetrate the narrow spine neck to join free ribosomes present in the post-synaptic area. C) A small granule containing the whole translation apparatus is translocated to the spine. In each instances, the close structure unfolds upon stimuli after releasing repressor molecules, either protein or RNA, to allow translation of its carried mRNA. Red lines with arrows indicate movements of the structures.