An Nkx-dependent enhancer regulates cGATA-6 gene expression during early stages of heart development

The evolutionarily conserved GATA-6 transcription factor is an early and pe rsistent marker of heart development in diverse vertebrate species. We prev iously found evidence for a functionally conserved heart-specific enhancer upstream of the chicken GATA-6 (cGATA-6) gene and in the present study we u sed transgenic mouse assays to further characterize this regulatory module. We show that this enhancer is activated in committed precursor cells withi n the cardiac crescent and that it remains active in essentially all cardio genic cells through the linear heart stage. Although this enhancer can acco unt for cGATA-6 gene expression early in the cardiogenic program, it is not able to maintain expression throughout the heart later in development. In particular, the enhancer is sequentially downregulated along the posterior to anterior axis, with activity becoming confined to outflow tract myocardi um. Enhancers with similar properties have been shown to regulate the early heart-restricted expression of the mouse Nkx2.5 transcription factor gene. Whereas these Nkx2.5 enhancers are GATA-dependent, we show that the cGATA- 6 enhancer is Nkx-dependent. We speculate that these enhancers are silenced to allow GATA-6 and Nkx2.5 gene expression to be governed by region-specif ic enhancers in the multichambered heart. (C) 2000 Academic Press.