Cardiovascular morphogenesis in zebrafish

Abstract

Much of our current understanding of early vertebrate cardiovascular development has come from study of avian and amphibian embryos (for a review of classical work on early specification of the heart, see Ref. [l]). The physical accessibility of these embryos and their developing cardiovascular tissues has made it possible to begin to examine the inductive interactions leading to heart formation. However, these organisms are relatively intractable to genetic analysis. Genetic screens have been instrumental in providing the tools to dissect complex developmental processes in invertebrates such as Drosophila melanogaster and C. elegans [2,3], but vertebrates more amenable to genetic analysis, notably the mouse, have embryos that develop inside the mother and are relatively inaccessible to observation and experimental manipulation, precluding screening for mutations affecting cardiovascular development. The zebrafish, Danio rerio, is a small tropical freshwater cyprinid with an approximately 3-month generation time. Adult fish measure approximately 1.5 inches in length, allowing large numbers of fish to be maintained economically in a relatively small space (Fig. 1A). Females produce several hundred eggs at frequent intervals, and the eggs are externally fertilized, so embryos are available for observation and experimental manipulation at all stages. In addition, the embryos are optically transparent until relatively late in embryogenesis, making it possible to observe development of internal organs directly and non-invasively (Fig. lC>. We have begun to explore whether the zebrafish might serve as a tractable model system for a combined embryologic and genetic analysis of cardiovascular development. In this review we describe particulars of the developing cardiovascular system in zebrafish and experimental and genetic methods that have been or could be applied to its study, and we illustrate the similarity of early cardiovascular development in zebrafish to that of mammals.