Fig. 4.

A putative role for FMRP in synaptic protein synthesis. (A) FMRP binds to its target mRNAs in the nucleus and helps export them to somatic cytoplasm (7, 42). (B) FMRP and its target mRNA are packaged into transport assemblies and travel, likely by way of microtubules, down dendrites toward synapses (15). (C) FMRP–mRNA transport assemblies may take the form of nontranslating granules near synapses where they await some synaptic signal (43, 44). (D) In response to activation of group 1 mGluRs (stimulated here with DHPG), phosphatidylinositol is cleaved into diacyl glycerol (DAG) and inositol triphosphate (IP₃), initiating the release of intracellular calcium (Ca²⁺ⁱ) and activation of PKC (26). (E) PKC activation triggers an enzyme cascade that, by means of many intermediates (broken arrow), signals nontranslating granules to release FMRP-bound target mRNA for translation.