The interaction of transmembrane Delta and Jagged/Serrate ligands with Notch receptors on neighboring cells is critically involved in cell specification during development. In zebrafish, the early expression of delta but not of jagged genes has been investigated in some detail. We have analyzed the sequence and embryonic expression pattern of the three zebrafish genes jagged1a, jagged1b, and jagged2. These genes, whose transcripts are detectable by in situ hybridization from early somitogenesis, are widely and dynamically expressed in embryos. Coexpression is limited, however, to the notochord and lens (jagged1a and jagged1b) and to the otic vesicle and pronephros (jagged1b and jagged2). Conversely, jagged1a and jagged2, both widely expressed in the central nervous system, are not coexpressed. jagged2 is also detected in the epidermis, newly formed somites, pharyngeal pouches, and pancreatic exocrine anlage and jagged1b in otic placodes and cell clusters close to the pancreatic islet. The similarities of the expression patterns of jagged and delta genes in zebrafish suggest that the Jagged and Delta ligands are functionally redundant or required in specific combinations in many differentiation processes.
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