1 Homeobox Genes in Cardiovascular Development

This chapter discusses the current literature relating to the patterns of expression and the possible functional roles for homeobox genes during the formation of the cardiovascular system. General background information on the structure and function of homeobox genes as a group is discussed in this chapter. Then, the chapter describes the formation and patterning of the vertebrate heart and vasculature, based on the studies, using zebrafish, Xenopus, chicken, and mouse embryos. Information available from the embryological and molecular studies is combined to provide a detailed description of the expression of the different homeobox genes that have been implicated in cardiovascular development. Where possible, the biological function of specific homeobox genes during cardiovascular development is discussed in this chapter. The cardiovascular system is among the first functional organ systems in the embryo. One of the fundamental goals of the biological research is to understand how the groups of embryonic cells become diversified and how these different groups work together to form functional tissues and organs. There is a popular view that homeobox genes are master regulators that control the expression of a large number of downstream genes. In at least some cases, e.g., the eyeless gene of Drosophila, homeobox genes appear to be capable of activating and maintaining a very complex developmental program. Significantly, the eyeless gene is able to initiate eye development at numerous ectopic locations.