Effects of follistatin and BMP4 proteins on early dorso-ventral patterningin chick

In Xenopus and zebrafish certain bone morphognetic proteins (BMPs), and pro teins that antagonise these by preventing their interaction with receptors, constitute a morphogen system in primary dorso-ventral patterning. This sy stem may be directly involved in the parallel processes, within mesoderm an d ectoderm, whereby the boundaries of the dorsal (paraxial) mesoderm and th e neural plate are established. The bird blastoderm, amenable to grafting t echniques and to direct exposure to specific proteins, has provided an oppo rtunity to explore the phylogenetic conservation of such antagonistic syste m. We have grafted the gastrular organiser (node) into hosts, testing the e ffects of prior exposure of either grafted or host tissue to Follistatin (a known antagonist of TGF beta superfamily ligands including BMP4) or to BMP 4 protein. Strong, converse effects are seen from the two agents, the most consistent being on the sizes of new dorsalised areas (second neural plates ) induced in host epiblast. Follistatin also enhances extension movements d ue to grafts, though without clear effect upon the rostro-caudal completene ss of new patterns. Neural induction in chick epiblast by grafted mouse nod es are also more extensive, after their pre-incubation in Follistatin. Foll istatin potentiates other, unknown but distinctive signals coming from the node, being unable to convert other non-inducing pieces of blastoderm into organisers on grafting. Pre-incubation of early blastoderms in BMP4 has suc h profound effects on normal dorsal axial development that host responsiven ess of these blastoderms as hosts to node grafts is difficult to assess. Fo llistatin has no such overt effect on host development, but greatly enhance s the competence of host epiblast to grafts of untreated nodes. Early chick BMP4 and BMP7 expressions are consistent with the proposed roles, though F ollistatin is probably an experimental tool only in the present study.