Models suggesting possible roles for Syt IX in controlling composition of SGs. (A) According to the “Retrieval” model, Syt IX regulates the transport of carriers destined to exit the ERC and the retrieval of recycling cargo from the MVBs/ISGs to the ERC. (B) According to the “Gatekeeper” model, Syt IX regulates export from the ERC and prevents ERC to MVBs/ISGs transport. N indicates nucleus; G, Golgi apparatus; L, lysosome; ERC, endocytic recycling compartment; ISG, immature secretory granule; EE, early endosome; LE, late endosome; MVB, multivesicular body.