HOW MANY SIGNALS DOES IT TAKE

Although the genetics of dorsal-ventral polarity which leads to mesoderm formation in Drosophila are understood in considerable detail, subsequent molecular mechanisms involved in patterning the mesoderm primordium into individual mesodermal subtypes are poorly understood. Two papers published recently((1,2)) suggest strongly that an inductive signal from dorsal ectoderm is involved in subdividing the underlying mesoderm, and present evidence that one of the signalling factors is Decapentaplegic (Dpp), a member of the bone morphogenetic protein subgroup of the Transforming Growth Factor-beta (TGF-beta) super family of proteins.