Identification of a cis-acting dendritic targeting element in the mRNA encoding the alpha subunit of Ca2+/calmodulin-dependent protein kinase II

In mammalian neurons a selected group of mRNAs, including the transcript en coding the alpha subunit of Ca2+/calmodulin-dependent protein kinase II, is found in dendrites. The molecular mechanisms underlying extrasomatic RNA t rafficking are not well described. It is thought that dendritic transcripts contain cis-acting elements that direct their selective subcellular sortin g. Here we report the identification of an extrasomatic targeting element i n the 3' untranslated region of the mRNA encoding the alpha subunit of Ca2/calmodulin-dependent protein kinase II. In primary hippocampal neurons, th is 1200-nucleotide-spanning, cis-acting element is sufficient to mediate de ndritic localization of chimeric reporter transcripts. The trafficking sign al does not share any striking sequence similarity with a previously charac terized dendritic targeting element in transcripts encoding the microtubule -associated protein 2. In dendrites of transfected primary neurons, recombi nant RNAs form granules with an average diameter of 0.45 mum that may repre sent preferential RNA docking sites or multimolecular transport units. Thes e findings imply that extrasomatic sorting of individual dendritic mRNAs in volves at least partially distinct molecular mechanisms, as well as large t rafficking complexes.