Cloning, tissue expression, and chromosomal location of the mouse insulin receptor substrate 4 gene

The insulin receptor substrates (IRSs) are key proteins in signal transduct ion from the insulin receptor. Recently, we discovered a fourth member of t his family, designated IRS-4, cloned its complementary DNA from the human e mbryonic kidney 293 cell Line, and characterized its signaling properties i n this cell line. As part of an investigation of the physiological role of this IRS, we have now cloned the mouse IRS-4 gene and determined its tissue expression and chromosomal location. The coding region of the mouse IRS-4 gene contains no introns, and in this regard is the same as that of the gen es for IRS-1 and -2. The predicted amino acid sequence of mouse IRS-I is hi ghly homologous with that of human IRS-4; the pleckstrin homology domain, t he phosphotyrosine-binding domain, and the tyrosine phosphorylation motifs are especially well conserved. The tissue distribution of IRS-4 in the mous e was determined by analysis for the expression of its messenger RNA by RT- PCR and for the protein itself by immunoprecipitation and immunoblotting. T he messenger RNA was detected in skeletal muscle, brain, heart, kidney, and liver, but the protein itself was not detected in any tissue. These result s indicate that IRS-4 is a very rare protein. The chromosomal locations of the mouse IRS-4 and IRS-3 genes were determined by interspecific backcross analysis and were found to be on chromosomes X and 5, respectively. As the mouse genes for IRS-1 and -2 are on chromosomes 1 and 8, respectively, each IRS gene resides on a different chromosome.