Peptide growth factors in amphibian embryogenesis: intersection of modern molecular approaches with traditional inductive interaction paradigms

Recent discoveries of the role peptide growth factors (PGFs) play in regula ting embryonic patterning and differentiation have profoundly influenced re search on the molecular biology of early amphibian embryogenesis. Several P GFs have been recognized to be present as endogenous components of amphibia n eggs and early embryos, while other PGFs - which are known from heterolog ous systems (e.g., Drosophila) - exert remarkable effects when injected as either protein or mRNA into eggs/embryos or when added to cultured embryoni c tissue. For a variety of reasons (reviewed herein) optimism abounds that an understanding in molecular terms of the classical Spemann and Nieuwkoop tissue interactions which are generally believed to drive embryonic pattern ing is within reach. A critical assessment of the interpretations of some o f the contemporary data on PGFs (included herein) should, however, temper s ome of that optimism. Likely, multiple rather than single PGFs act in a com binatorial fashion to contribute to individual patterning events. As well, substantial redundancy in PGF regulatory circuits probably exists, so the h eavy reliance on tissue culture assays and overexpression studies which cha racterize much recent research needs to be circumvented. Potential experime ntal approaches for "next generation" experiments are discussed.