... plate mesoderm, posterior limb bud and flank mesenchyme, a pattern reminiscent of the distribution of polarizing activity. The polarizing activity is determined by the ability of a certain region to induce digit duplications when grafted into the anterior margin of a host limb bud. Several manipulations...

... ridge in response to FGF4 in both mouse and chick embryos exists throughout the flank as does ability of mesenchyme to provide a polarizing region signal. In addition, neck tissue has weak polarizing activity. We show, in chick embryos, that polarizing activity of tissues correlates with the ability...

... an expression pattern complementary to that of shh , a mediator of polarizing activity in the limb bud. Local application of Sonic hedgehog (Shh) and Fibroblast Growth Factor (FGF), in addition to ectodermal apical ridge removal experiments suggest the existence of a negative feedback loop between Alx-4 and Shh...

..., P19, transfected with a Shh expression vector shows low polarizing activity, but when cultured with retinoic acid, duplications like those induced by the polarizing region (ZPA) arise. Complete duplications are also obtained by cotransfecting P19 Shh cells with a constitutively active human retinoic...

... limb buds leads to reduction of polarizing activity and defects along the anteroposterior axis. * Present address: Laboratory of Genetic Disease Research, National Center for Human Genome Research, National Institutes of Health, Building 49/4A80, Bethesda, MD 20892, USA 20 June 1995...

... caused by polarizing grafts, since additional digits with posterior character are present at the anterior side of the limb. Such observations suggest that lst D limb buds might contain a genetically determined ectopic region of polarizing activity. Accordingly, we show that mutant embryos ectopically...

... activity, has the properties predicted for a ligand for the transmembrane receptor encoded by the Toll gene. Using a bioassay to follow activity, we purified a 24×10 3 M r protein that has polarizing activity. The purified protein is recognized by antibodies to the C-terminal half of the Spätzle protein...

... ectodermal ridge and signalling by the polarizing region. To test this possibility, we removed the posterior apical ectodermal ridge of chick wing buds and assayed posterior mesenchyme for polarizing activity. When the apical ectodermal ridge is removed, there is a marked decrease in polarizing activity...

...Amata Hornbruch; Lewis Wolpert ABSTRACT The presence of polarizing activity in the limb buds of developing avian embryos determines the pattern of the anteroposterior axis of the limbs in the adult. Maps of the spatial distribution and the strength of the signal within limb buds of different stages...