HEMATOPOIETIC MUTATIONS IN THE ZEBRAFISH

We have identified mutations that perturb the formation or differentia tion of the first embryonic blood cells in the zebrafish embryo, These 'primitive' red blood cells originate in the intermediate cell mass o f the trunk, a derivative of the dorsal lateral plate mesoderm. By tra nsfusion of blood between embryos we demonstrate that this cohort of c ells provides the embryo with all, or nearly all, of its blood cells u ntil at least day 5 postfertilization, Larval lethal mutations generat ed by ENU mutagenesis affect different steps In the development of the se cells, Some cause defects in precursor generation, others defects i n differentiation, and others an increase in cellular photosensitivity .