Endothelial cell (EC) precursors, termed angioblasts, form primitive vascular plexuses de novo, a process termed vasculogenesis (1–3). Cells of the primitive vascular plexus further differentiate into arterial, venous, endocardial, and lymphatic ECs. New vessels also sprout out from the existing vessels via angiogenesis. Angioblasts are highly migratory, often originating far from their destination (1,3). By tracking the migratory patterns and lineage specification of EC precursors, the mechanisms involved in EC commitment and diversity can be defined more precisely. The fate maps of groups of cells provide clues regarding the tissue–tissue interactions involved in EC differentiation and vessel development. Single-cell labeling and tracing can determine the specific timing and site of lineage segregation. This chapter describes the ontogeny of cardiac and noncardiac ECs as revealed by genetic and nongenetic fate mapping and lineage analysis.

CELL TAGGING METHODS

Successful fate mapping or lineage analysis depends on a reliable cell tagging method that allows researchers to label a defined group of cells and to restrict the labeling to its progeny without dilution or horizontal spread. Several methods of genetic and nongenetic cell labeling have been developed.

Nongenetic Approaches

Labeling with a lipophilic fluorescent dye, such as DiI (1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanine · perchlorate), is a widely used nongenetic cell labeling method for fate mapping studies (4,5). DiI stably integrates into cell membranes and generates a high fluorescent signal, but exhibits little diffusion to adjacent cells and insignificant cell toxicity. Because of their stable integration into the cell membrane, lipophilic dyes are passed mainly to the progeny of the labeled parental cells.