Equivalent genetic roles for bmp7/snailhouse and bmp2b/swirl in dorsoventral pattern formation

A bone morphogenetic protein (BMP) signaling pathway acts in the establishm ent of the dorsoventral axis of the vertebrate embryo. Here we demonstrate the genetic requirement for tn two different Bmp ligand subclass genes for dorsoventral pattern formation of the zebrafish embryo. From the relative e fficiencies observed in Bmp ligand rescue experiments, conserved chromosoma l synteny, and isolation of the zebrafish bmp7 gene, me determined that the strongly dorsalized snailhouse mutant phenotype is caused by a mutation in the bmp7 gene. We show that the original snailhouse allele is a hypomorphi c mutation and we identify a snailhouse/bmp7 null mutant. We demonstrate th at the snailhouse/bmp7 null mutant phenotype is identical to the presumptiv e null mutant phenotype of the strongest dorsalized zebrafish mutant swirl/ bmp2b, revealing equivalent genetic roles for these two Bmp ligands, Double mutant snailhouse/bmp7; swirl/bmp2b embryos do not exhibit additional or s tronger dorsalized phenotypes, indicating that these Bmp ligands do not fun ction redundantly in early embryonic development. Furthermore, overexpressi on experiments reveal that Bmp2b and Bmp7 synergize in the ventralization o f wildtype embryos through a cell-autonomous mechanism, suggesting that Bmp 2b/Bmp7 heterodimers mag act in vivo to specify ventral cell fates in the z ebrafish embryo.