HOW MANY SIGNALS DOES IT TAKE

Although the genetics of dorsal-ventral polarity which leads to mesode rm formation in Drosophila are understood in considerable detail, subs equent molecular mechanisms involved in patterning the mesoderm primor dium into individual mesodermal subtypes are poorly understood. Two pa pers published recently((1,2)) suggest strongly that an inductive sign al from dorsal ectoderm is involved in subdividing the underlying meso derm, and present evidence that one of the signalling factors is Decap entaplegic (Dpp), a member of the bone morphogenetic protein subgroup of the Transforming Growth Factor-beta (TGF-beta) super family of prot eins.