Haploinsufficiency of the cardiac transcription factor Nkx2-5 variably affects the expression of putative target genes

SPECIFIC AIMSHeterozygous mutations of transcription factors cause a number of known human diseases, including cancer, birth defects, and syndromes. The identification of genes that are “direct” transcriptional targets is necessary to elucidate the molecular pathogenesis. Two forms of evidence are commonly offered to prove that a transcription factor directly regulates a gene. First, the suspected target must be abnormally expressed in a cell or tissue depleted of the factor, as in a homozygous knockout mouse. Second, the promoter of the putative target gene must contain binding sites for the transcription factor and transactivate a reporter gene construct when coexpressed with the transcription factor in cell culture or in transgenic animals. These two experimental strategies have yielded important insights, but generalizations about mechanisms of disease may be flawed because the results are obtained outside the physiologic range of transcription factor concentration.Nkx2-5 is an evolutionarily conserve...