GTP cyclohydrolase I gene expression in the brains of male and female hph-1 mice

The hph-1 mouse is characterized by low levels of GTP cyclohydrolase I (GTP CH) and tetrahydrobiopterin. A quantitative double-label in situ hybridizat ion technique was used to examine CNS GTPCH mRNA expression within serotoni n, dopamine, and norepinephrine neurons of male and female wild-type and hp h-1 mice. In wild-type male and female animals the highest levels of GTPCH mRNA expression were observed within serotonin neurons, followed by norepin ephrine and then dopamine neurons. Wild-type female animals were found to e xpress lower levels of GTPCH mRNA in each cell type when compared with leve ls seen in wild-type males. GTPCH mRNA abundance in all three cell types wa s lower in hph-1 male than in wild-type male mice, with the greatest reduct ion in serotonin neurons. GTPCH mRNA levels were also lower in hph-1 female than in wild-type female mice, again with the greatest reduction occurring in serotonin neurons. Comparison of hph-1 male and hph-1 female mice revea led that the sex-linked difference in GTPCH mRNA expression observed in wil d-type neurons was only present within female dopamine neurons. Overall, th ese results indicate that not only are basal levels of GTPCH mRNA expressio n heterogeneous across wild-type murine monoamine cell types but that gene expression is also modified in a sex-linked and cell-specific fashion by th e hph-1 gene locus. The hph-1 mutation does not lie within the GTPCH mRNA c oding region, The 5' flanking region of the GTPCH gene was cloned and seque nced and shown to be identical for both wild-type and hph-1 genomic DNA, Tr ansient transfection assays performed in PC12 cells demonstrated that this 5' flanking region was sufficient to initiate transcription of a luciferase reporter gene. Although the hph-1 mutation does not lie within the 5' flan king region of the GTPCH gene, this region of the gene can function as a co re promoter and is thus crucial to the control of GTPCH gene expression.