Molecular Cloning and Tissue Expression Analysis of the Bovine IWS1 Gene in an Imprinted BTA2 Region

Our previous whole genome scan identified the proximal end of bovine chromosome 2 as containing a putative parent-of-origin effect quantitative trait locus (POE-QTL) affecting postnatal growth in cattle. As a follow-up, we embarked on a search for possible positional candidate genes in this region using both bioinformatics and experimental approaches. A search of the human and mouse genomes of known and putative imprinted genes indicated that the homolog of S. cerevisiae serine protease inhibitor 1 (IWS1) is found in this region. This gene is part of a transcription factor complex that regulates gene expression. To further characterize this gene in cattle genome, we amplified the gene in a cDNA panel of 18 cattle tissues and found it expressed in all of them. We sequenced the mRNA and found 99.9% homology with the predicted mRNA sequence in cattle. A comparison of this sequence with the predicted mRNA sequence in sheep and pig shows 97.9 and 92.9% homology, respectively. A phylogenetic analysis of the protein sequence predicted from these mRNAs and those of dog, panda, horse, human, marmoset, mouse, rat, elephant, opossum and platypus, using the lizard protein as an out group, shows high conservation among all the eutherian mammals but not as much with marsupials and monotremes. Due to the conservation of this gene in eutherian, as well as the previous report showing evidence of imprinting expression, this is a good candidate gene for the POE-QTL and its further characterization and analysis could be valuable for livestock improvement.

Key words: Imprinting, growth, QTL, cattle, bovine chromosome 2, parent-of-origin effects