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 interact with other proteins to control embryogenesis and tumorigenesis. We present the characterization of a zebrafish pbx CDNA that appears to encode a novel family member, pbx4. pbx4 RNA is maternally deposited and is detected throughout the zebrafish embryo during blastula stages. It becomes excluded from ventroanterior structures at late gastrula stages and is detected within the forming central nervous system during segmentation stages. pbx4 expression 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 Pbx4/Meis3 and Pbx4/Hoxb1b, but not Meis3/Hoxb1b could be generated. A novel trimeric complex containing Pbx4, Meis3, and Hoxb1b was also formed. We speculate that complexes with different combinations of Pbx4, Meis3, and Hoxb1b specify different developmental fates during vertebrate embryogenesis. Dev Dyn 2000;217:109-119.