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The GATA-4/5/6 genes encode transcription factors implicated previously in the regulation of cardiac-specific differentiation programs. However, recent analyses of mouse GATA-4 null mutations found evidence for function in endoderm development (in vitro) and embryonic morphogenesis (in vivo). Whether each of the three cardiac-associated GATA factors function within distinct or common developmental programs was previously untested; past studies defined specific and distinct roles for each of the GATA-1/2/3 genes in embryonic hematopoiesis. In this study, we compare the transcript patterns of cGATA-4/5/6 during chick embryogenesis. Each of the three GATA factors is expressed in a similar pattern within gastrulating cells of the primitive streak, prior to determination of the cardiomyocyte progenitors, and later within the lateral plate mesoderm and associated endoderm layer. The patterns overlap but extend beyond the presumptive cardiomyocyte population expressing cNkx-2.5. Later in development, cGATA-4/5/6 are all transcribed throughout the differentiating heart, in similar but not identical patterns, within the endocardium, myocardium, and great vessels. In order to test the function of GATA factors during chick cardiogenesis, embryos were cultured in vitro in the presence of antisense oligomers designed to deplete specifically transcripts encoding cGATA-4/5/6, beginning around stage 7. When oligomers are used to target transcripts for all three genes, a high percentage of the embryos develop abnormal hearts related to the failure to form a normal primitive heart tube. In the most severe phenotype, cardiac bifida results in two bilateral beating hearts. In some embryos, the paired heart primordia undergo partial fusion but fail to form a single looping heart tube. In all cases, cellular differentiation is not obviously affected, as the abnormal hearts form beating tissue. Depletion of transcripts encoding any single GATA factor, or any combination of two GATA factors, does not affect development. The partial depletion of all three genes in chick results in a remarkably similar phenotype compared to the null GATA-4 mutation in mouse. Therefore, in the chick, each of the GATA-4/5/6 genes functions in a common pathway, at the time of cardiac crescent formation, for regulating early embryonic cardiac morphogenesis, apparently associated with embryonic folding or the migration of primordia to form a primitive tube. |
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