Genetic Society of America Meeting 2006, San Diego, CA. Abstract 178A.
Ataxia-telangiectasia (AT) is recessive autosomal disorder characterized by loss of cerebellar function, progressive dysarthria and choreoathetosis. In addition to neurodegeneration the typical signs of AT are immune deficiencies, sterility, cancer predisposition, chromosomal instability and radiation sensitivity. Existing mouse AT models do not reflect the extent of neurological disorders found in human. In order to develop a porcine model for AT, we sequenced ATM transcripts, characterized the 5'-untranslated region (5' UTR), identified splice variants and developed constructs for gene targeting. Similar to humans, the porcine ATM gene exhibits extensive alternative splicing. In contrast with humans it involved not only the 5' UTR but also coding regions. Six splice variants with 3 alternative exons were observed in the 5' UTR, three of them spliced out the first coding exon, altering the translation start and giving rise to the putative protein lacking the N-terminus substrate binding domain. Real time PCR analysis revealed variable levels of ATM expression in 24 different tissues with the impact of the longest splice variant to be not less than 60% of total ATM transcripts in all tissues. The majority of AT patients carry truncating ATM mutations resulting in prematurely terminated proteins that are highly unstable. Thus, to knockout the ATM gene, we developed two gene targeting constructs by introducing truncation mutations shortly after known and putative translation starts, according to splice variants detected. The similarity of the porcine to the human gene in extensive alternative splicing supports our goal of creating a more relevant model for AT than in the mouse.
(This work was supported in part by USDA/NRI-CSREES grant AG2001-35205-11698 and USDA-ARS AG58-5438-2-313 and AT Children's Project).