Genomic structure and promoter analysis of the mouse neutral ceramidase gene

We report here the molecular cloning of the mouse neutral ceramidase gene and its promoter analysis. The gene, composed of 27 exons ranging in size from 40 to 292 bp, spans more than 70 kb. Analysis of the 5(')-flanking region of the ceramidase genes revealed that the first exon of the gene of mouse liver was exactly the same as that of mouse kidney and Swiss 3T3 fibroblasts but completely different from that of mouse brain. The putative promoter regions of liver and brain ceramidase genes contained several well-characterized promoter elements such as GATA-2, C/EBP, and HNF3beta but lacked TATA and CAAT boxes, a typical feature of a housekeeping gene, although the expression is regulated in a tissue-specific manner. Interestingly, a GC box was exclusively found in the putative promoter of mouse liver whereas potential AP1 and AP4 binding sites were present in that of mouse brain. By a luciferase reporter gene assay, it was shown that the GC-rich region, which exists just upstream of the first exon, conferred the promoter activity in Swiss 3T3 cells.     

Complex structure and regulation of expression of the rat gene for inward rectifier potassium channel Kir7.1

Genomic organization of the rat inward rectifier K(+) channel Kir7.1 was determined in an attempt to clarify how multiple species of its mRNA are generated in a tissue-specific manner and how its expression is regulated. The rat Kir7.1 gene spans >40 kilobases (kb) and consists of eight exons; the first four exons encode the 5'-untranslated region that is unusually long ( approximately 3 kb). The coding region is located in exons 5 and 6. In the testis, exon 4 is processed as four exons (4a-4d), whereas it is recognized as a single exon in the small intestine. The three major species of rat Kir7.1 mRNA (1.4, 2.2, and 3.2 kb) were found to arise from alternative usage of the two promoters and polyadenylation signals and by alternative splicing of the 5'-noncoding exons. The splicing pattern of the 5'-noncoding exons is quite complex and highly tissue-specific, suggesting that complex mechanisms may operate to regulate the Kir7.1 expression. Deletion and mutational analysis of the promoter activity indicated that the rat Kir7.1 gene is regulated by cAMP through a CCAAT element. The cAMP induction was also demonstrated using the rat follicular cell line FRTL-5 endogenously expressing Kir7.1.