Widespread expression of an extended peptide sequence of GATA-6 during murine embryogenesis and non-equivalence of RNA and protein expression domains.

The transcription factor GATA-6 is known to be a critical determinant of early vertebrate development. We have shown previously that mammalian GATA-6 genes have the potential to encode two protein isoforms, resulting from alternative, in-frame, initiator methionine codons. We have generated GATA-6 antibodies, including one specific to the longer form of GATA-6, and by immunohistochemical analysis we demonstrate here that the longer protein, which is the more potent transcriptional transactivator, is widely expressed in vivo. In accordance with previous RNA expression studies, GATA-6 protein was found to be abundant within regions of the gut and pulmonary systems, in addition to the heart myocardium. We also report novel GATA-6 expression within sites of chondrogenesis derived from cranial neural crest and sclerotomes. Surprisingly however, levels of GATA-6 protein were substantially reduced within the endocardial cushions and outflow tract of the heart. These are regions which express the highest levels of GATA-6 RNA within the heart.