Dendritic and postsynaptic protein synthetic machinery

There is a growing body of evidence that local protein synthesis beneath sy napses may provide a novel mechanism underlying plastic phenomena. In vivo and in vitro biochemical data show that dendrites can perform translation a nd glycosylation. Using antibodies directed against the eukaryotic protein synthetic machinery, we sought to identify the structures implicated in non perinuclear translation, namely dendritic and postsynaptic protein synthesi s. We performed a morphological and immunocytochemical analysis of ventromedia l horn rat spinal cord neurons using both light and electron microscopy, We show at the cellular level that, in vivo, protein synthesis macrocomplexes (ribosomes and elF-2) as well as the endomembranous system implicated in c otranslational and posttranslational modifications (endoplasmic reticulum a nd Golgi cisternae) penetrated some dendrites. Membrane-limited organelles of different shape and size are present close to the postsynaptic different iations of most synapses, independently of their localization on the neuron al surface. We demonstrate (1) that some cisternae are immunoreactive for a ntibodies against ribosomal proteins and elF-2, and (2) that markers of end oplasmic reticulum (BiP), intermediate compartment, and Golgi complex (rab1 , CTR433, TGN38) label subsets of these subsynaptic organelles. Therefore, these findings indicate that synapses are equipped with the esse ntial elements required for the synthesis and insertion of a well folded an d glycosylated transmembrane protein.