A novel Pbx family member expressed during early zebrafish embryogenesis forms trimeric complexes with Meis3 and Hoxb1b

pbx genes encode homeodomain-containing transcriptional regulators that int eract with other proteins to control embryogenesis and tumorigenesis, We pr esent the characterization of a zebrafish pbx CDNA that appears to encode a novel family member, pbx4, pbx4 RNA is maternally deposited and is detecte d throughout the zebrafish embryo during blastula stages, It becomes exclud ed from ventroanterior structures at late gastrula stages and is detected w ithin the forming central nervous system during segmentation stages, pbx4 e xpression overlaps with that of two other homeobox genes, hoxb1b and meis3, in the region of the presumptive caudal hindbrain during gastrula stages, In vitro binding experiments revealed that protein complexes containing Pbx 4/Meis3 and Pbx4/Hoxb1b, but not Meis3/Hoxb1b could be generated. A novel t rimeric complex containing Pbx4, Meis3, and Hoxb1b was also formed. We spec ulate that complexes with different combinations of Pbx4, Meis3, and Hoxb1b specify different developmental fates during vertebrate embryogenesis. (C) 2000 Wiley-Liss, Inc.