A ZEBRAFISH HOMOLOG OF THE DROSOPHILA NEUROGENIC GENE NOTCH AND ITS PATTERN OF TRANSCRIPTION DURING EARLY EMBRYOGENESIS

We describe here the primary structure of a zebrafish homologue of the Drosophila neurogenic gene Notch and its pattern of mRNA accumulation during embryogenesis. The gene produces a 8.5 kb transcript encoding a putative transmembrane protein with a high degree of sequence simila rity to members of the Notch family, comprising 36 EGF-like repeats, t hree lin-12/Notch repeats, six cdc10/SWI6 repeats, OPA repeats and a P EST sequence. Transcription of the zebrafish Notch gene is spatially a nd temporally regulated. A high density of transcripts, most probably of maternal origin, can already be detected in the 2-cell stage. Durin g pregastrulation stages, RNA is present in all cells. However, follow ing gastrulation, transcripts accumulate in specific regions of the em bryo following a rapidly changing pattern. In some of these regions, c ell divisions take place at the time of Notch expression, in others pr ocesses of cell differentiation. This holds true for various mesoderma l derivatives, such as the prospective notochord, and for different ne ural primordia, such as the neural plate and the brain vesicles. This pattern of transcript accumulation suggests a role for the zebrafish N otch homologue in processes of regionalization and cell diversificatio n.