Gene duplication of zebrafish JAK2 homologs is accompanied by divergent embryonic expression patterns: Only jak2a is expressed during erythropoiesis

Members of the JAK family of protein tyrosine kinase (PTK) proteins are req uired for the transmission of signals from a variety of cell surface recept ors, particularly those of the cytokine receptor family. JAK function has b een implicated in hematopoiesis and regulation of the immune system, and re cent data suggest that the vertebrate JAK2 gene may play a role in leukemia , We have isolated and characterized jak cDNAs from the zebrafish Danio rer io, The zebrafish genome possesses 2 jak2 genes that occupy paralogous chro mosome segments in the zebrafish genome, and these segments conserve synten ic relationships with orthologous genes in mammalian genomes, suggesting an ancient duplication in the zebrafish lineage. The jak2a gene is expressed at high levels in erythroid precursors of primitive and definitive waves an d at a lower level In early central nervous system and developing fin buds. jak2b is expressed in the developing lens and nephritic ducts, but not in hematopoietic tissue. The expression of jak2a was examined in hematopoietic mutants and found to be disrupted in cloche and spadetail, suggesting an e arly role in hematopoiesis, Taken together with recent gene knockout data i n the mouse, we suggest that jak2a may be functionally equivalent to mammal ian Jak2, with a role in early erythropoiesis. (C) 1999 by The American Soc iety of Hematology.