The zygotic expression of zebrafish trebf during embryogenesis is restricted to the embryonic shield and its derivatives

We have identified a zebrafish gene trebf that shows an overall similarity of 51.5% and 55.1% in amino acid sequence with human and mouse TREB5/hXBP1/ HTF, respectively. Northern hybridization reveals that trebf mRNA is expres sed throughout the life cycle of zebrafish. Whole-mount in situ hybridizati on detects an expression pattern of trebf in zebrafish that is very differe nt from that of mammalian TREB5. Just before the onset of gastrulation, tre bf transcripts are accumulated in the dorsal blastoderm margin and subseque ntly in the forming organizer. During gastrulation, the trebf-positive cell s in the organizer migrate toward the animal pole and form two distinct dom ains. The cells in the anterior leading expression domain ultimately differ entiate into hatching gland, whereas those in the following domain form the notochord.