Genomic organization and expression analysis of mouse kynurenine aminotransferase II, a possible factor in the pathophysiology of Huntington's disease

Decreased levels of the endogenous neuroprotectant kynurenic acid (KYNA) ha ve been observed in the brain of Huntington's Disease (HD) patients and may be related to neuronal loss in this disorder. This reduction may be caused by a dysfunction of kynurenine aminotransferase II (KAT II), the major enz yme responsible for the synthesis of KYNA in the brain. Towards understandi ng the role of KAT II in HD, we isolated and characterized the cDNA sequenc e and determined the genomic organization of mouse KAT II (mKat-2). The ful l length mKat-2 cDNA is 1812 bp, encoding 425 amino acids, and shares 89.9% amino acid similarity with the rat Kat-2 sequence. The gene for mKat-2 is com: posed of 13 exons divided by 12 intronic sequences. Northern blot anal ysis demonstrated that mKat-2 mRNA is mainly expressed in kidney and liver. RT-PCR showed mKat-2 expression in the brain starting from at least d11 of embryonic development. An alternative isoform mKat-2 beta, derived from th e usage of novel exons, shows a different expression pattern from mKnr-2. W estern blot analysis of various mouse tissues shows a 40-kDa protein in bra in, heart, kidney, and liver. In the kidney and liver an additional 45-kDa isoform was detected. Use of the BSS chromosomal mapping panel from The Jac kson Laboratory indicates that the mKat-2 gene co-segregates with polymorph ic markers D8Mit129 and D8Mit128 on mouse Chr 8. Knowledge of the genomic o rganization, the isoform tissue-specific expression patterns, the chromosom al localization of mKat-2, and the reagents generated here, will provide th e tools for further studies and allow generation and characterization of mi ce that are nullizygous for mKat-2.