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/hXBP-1/HTF, respectively. Northern hybridization reveals that trebf mRNA is expressed throughout the life cycle of zebrafish. Whole-mount in situ hybridization detects an expression pattern of trebf in zebrafish that is very different from that of mammalian TREB5. Just before the onset of gastrulation, trebf transcripts are accumulated in the dorsal blastoderm margin and subsequently in the forming organizer. During gastrulation, the trebf-positive cells in the organizer migrate toward the animal pole and form two distinct domains. The cells in the anterior leading expression domain ultimately differentiate into hatching gland, whereas those in the following domain form the notochord.