DEVELOPMENTAL BIOLOGY OF THE VERTEBRATE HEART

This paper summarizes the development of the heart from the formation of the heart mesoderm to cardiac septation. A brief account of morphol ogical changes is provided, but attention is focused on mechanisms rat her than on morphologic descriptions. Heart induction and differentiat ion, and the expression of cardiac specific proteins, are reviewed. Ne w developments in these areas include the possible role of cell surfac e proteins and peptide growth factors in the segregation of the splanc hnic mesoderm and in cardiac commitment. Past; and recent experiments indicate that the heart morphogenetic information is engraved in the p recardiac mesoderm. In spite of this, specific differentiative signals can be overridden experimentally demonstrating the unstability of the cardiac phenotype at the early heart tube stage. The relationship bet ween differentiation and morphogenesis is analyzed. While cardiac diff erentiation appears to be a prerequisite for morphogenesis, a number o f experiments indicate that differentiation can proceed in the absence of any morphogenesis. Formation of the heart loop is separated into t wo different components; looping itself and the acquisition of handedn ess. Late heart morphogenesis is explained in terms of differential ti ssue growth and tissue remodeling. This not only includes morphogeneti c changes intrinsic to the heart but the addition of new cell types (n eural crest, epicardium, vessels, nerves) that become integrated into the developing heart. The contribution of specific mechanisms to our u nderstanding of heart development, such as cell death and hemodynamics , is also analyzed. (C) 1996 Wiley-Liss, Inc.