CHARACTERIZATION OF THE RAT HIPPOCALCIN GENE - THE 5'-FLANKING REGIONDIRECTS EXPRESSION TO THE HIPPOCAMPUS

Hippocalcin is an EF-hand [Persechini A. et al. (1989) Trends Neurosci . 12, 462-467] Ca2+ binding protein encoded by a neuron-specific gene. A detailed atlas of hippocalcin messenger RNA expression in the adult rat brain was compiled using in situ hybridization. Highest levels of messenger RNA are found in the hippocampus, where messenger RNA is lo calized in proximal dendrites of CA pyramidal cells. Expression is als o seen in other brain regions, including the neocortex, caudate-putame n, taenia tecti, claustrum, olfactory tubercle, anterior olfactory nuc leus, and granule cell and glomerular layers of the olfactory bulb. Th e rat hippocalcin gene spans approximately 9 kb and consists of three exons, separated by introns of 6.7 and 0.25 kb. Sequence analysis of t he putative proximal promoter region identified two clusters of multip le E-box sites which may regulate the cell-specific expression. Two la cZ fusion constructs carrying 0.9 and 3.4 kb of rat hippocalcin gene u pstream region were used to create transgenic mice. With the 3.4 kb co nstruct, transgene expression varied between founder mice, but was alw ays found in the dentate gyrus and CA1-CA4 regions of the hippocampus, thus partly mimicking the expression of the endogenous gene. For the 0.9 kb construct, the levels of lacZ expression were weaker and more v ariable. Neither construct showed expression in any peripheral tissues examined. To establish an in vitro model of transcriptional regulatio n, the 3.4 and 0.9 kb 5' upstream regions were fused to a promoterless reporter gene encoding chloramphenicol acetyltransferase and transien tly transfected into the hippocalcin-positive NG-108 cells. The 3.4 kb construct was strongly expressed, whilst the 0.9 kb construct was not expressed. In this paper, we describe the detailed expression pattern of the rat hippocalcin gene, the gene structure and its neuron-specif ic promoter. Copyright (C) 1996 IBRO. Published by Elsevier Science Lt d.