CaM I mRNA is localized to apical dendrites during postnatal development of neurons in the rat brain

In the rat, a single calmodulin (CaM) protein is encoded by three separate genes which produce five different transcripts. The significance of the multiple CaM genes is not known; however, individual CaM transcripts could be targeted to specific intracellular sites. In this report, the cellular distribution of CaM I mRNAs was analyzed in the postnatal rat brain. The 4.0-kb CaM I transcript was present in neuronal cell bodies and also localized to apical dendritic processes. In cerebral cortical neurons, the 4.0-kb CaM I mRNA was detected in apical dendrites at postnatal day (PD) 5 to 15. In hippocampal neurons, this CaM message was present in dendritic processes from PD S to 20, whereas in Purkinje neurons it was detected in dendrites at PD 15 and 20. The presence of the 4.0-kb CaM I mRNA in dendrites of the rat brain supports the notion of targeting transcripts derived from the CaM multigene family to discrete intracellular destinations.