REGIONALIZATION OF MYOCARDIAL GENE-EXPRESSION - IMPLICATIONS FOR HEART MORPHOGENESIS

The vertebrate heart is composed of a series of distinct morphological compartments which are established in the early embryo and remodelled during subsequent cardiogenesis. Transgenic mouse studies have shown that these compartments, including right and left cardiac chambers, co rrespond to a series of independent transcriptional units. These resul ts, supported by the transiently compartmentalised expression profiles of a subset of endogenous cardiac genes, reveal a modular basis to tr anscription in the myocardium. Regionalised expression domains provide informative markers with which the contribution of different regions of the embryonic heart to particular structures of the adult heart can be followed during normal cardiogenesis, and, using mouse models of c ardiac malformations, during abnormal heart development. Congenital he art disease in man is frequently the result of abberant interactions b etween different cardiac compartments. Regionalisation within the myoc ardium becomes evident at the time of cardiac looping, and is the prod uct of two patterning inputs: firstly position along the anterior-post erior axis of the early heart tube, and secondly embryonic laterality signals which dictate cardiac asymmetry. Recent experiments have begun to elucidate the role of different cardiac transcription factors in d irecting regionalised expression domains in the embryonic heart.