CHARACTERIZATION OF ZEBRAFISH MUTANTS WITH DEFECTS IN EMBRYONIC HEMATOPOIESIS

As part of a large scale chemical mutagenesis screen of the zebrafish (Danio rerio) genome, we have identified 33 mutants with defects in he matopoiesis, Complementation analysis placed 32 of these mutants into 17 complementation groups, The allelism of the remaining 1 blood mutan t is currently unresolved, We have categorized these blood mutants int o four phenotypic classes based on analyses of whole embryos and isola ted blood cells, as well as by in situ hybridization using the hematop oietic transcription factors GATA-1 and GATA-2, Embryos mutant for the gene moonshine have few if any proerythroblasts visible on the day ci rculation begins and normal erythroid cell differentiation is blocked as determined by staining for hemoglobin and GATA-1 expression, Mutati ons in five genes, chablis, frascati, merlot, retsina, thunderbird and two possibly unique mutations cause a progressive decrease in the num ber of blood cells during the first 5 days of development, Mutations i n another seven genes, chardonnay, chianti, grenache, sauternes, weibh erbst and zinfandel, and two additional mutations result in hypochromi c blood cells which also decrease in number as development proceeds, S everal of these mutants have immature cells in the circulation, indica ting a block in normal erythroid development. The mutation in zinfande l is dominant, and 2-day old heterozygous carriers fail to express det ectable levels of hemoglobin and have decreasing numbers of circulatin g cells during the first 5 days of development, Mutations in two genes , freixenet and yquem, result in the animals that are photosensitive w ith autofluorescent blood, similar to that found in the human congenit al porphyrias, The collection of mutants presented here represent seve ral steps required for normal erythropoiesis, The analysis of these mu tants provides a powerful approach towards defining the molecular mech anisms involved in vertebrate hematopoietic development.