By Northern blot analysis with the digoxigenin-labeled antisense RNA probes of the noncoding regions, the transcripts of three calmodulin (CaM) genes, CaMI, CaMII, and CaMIII, were separately detected in 12 different tissues of adult Wistar albino rats, without any cross-hybridization. The mRNAs of all three CaM genes were abundant in the central nervous system (CNS) as well as in the testis, although ubiquitous expression was detected at low levels in the other tissues. There were subtle but significant differences in the tissue-specific distribution of the three CaM gene RNAs. By in situ hybridization, strong hybridization of the three CaM gene probes was observed in common in large projection neurons of the CNS: the hippocampal pyramidal cells, the cerebellar Purkinje cells, and the large neurons of the cerebral neocortex, the pyriform cortex, the mesencephalon, the pons, and the spinal cord. The expression of the three CaM genes was at lower levels in small interneurons of the CNS. These profiles of expression were almost the same among the three CaM genes. Thus, all three CaM genes were coordinately expressed in neurons of the adult rat CNS. Certain regulatory mechanisms of the three CaM genes seemed to mediate similar tissue- and cell type-specific expression in the CNS.

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