Résumé
This chapter describes how different regional identities may be assigned along the anteroposterior (AP) body axis of the developing zebrafish embryo, namely in the head, trunk, and tail regions. It provides a description on the isolation of the Hox cluster genes in zebrafish. Although the characterization of this family of genes in the frog, chick, mouse, and human has often been dogmatically reported in the literature and textbooks as applicable to all vertebrates, this chapter describes important differences in the genomic organization and expression patterns of the zebrafish Hox cluster genes relative to the Hox cluster genes in tetrapods. It has been found that the zebrafish Hox cluster genes are useful markers for regions of the zebrafish hindbrain and trunk; however, as in tetrapods, the genes which are studied here to date do not appear to have unique expression patterns within the tail region. To show how different regional identities may be specified in the vertebrate tail region, this chapter describes cell marking and cell movement analyses of the developing tail bud in the living zebrafish embryo. It was found that although the tail bud region of the zebrafish, like most vertebrates, appears initially as a homogeneous blastema without easily recognizable germ layer distinctions, it is actually a very ordered tissue with distinct fate-map regions of cell fate identity. In addition, this chapter provides a set of cell movements that appear to be unique to the tail bud region.