Organizer - a Milestone of a Half-century from Spemann

acid action activity amphibian animal Arch archenteron axial Biol blastoderm blastopore blastula capacity caused cells chick competence containing cultured cytoplasmic determination differentiation dorsal dorsal lip early ectoderm effect embryo endoderm experiments explants extract factor filter formation formed fraction further gastrula gene gradient graft head histone Holtfreter important induction inductor influence invagination isolated later layer lens liver marginal zone mark material mechanism mesodermal method morphogenetic movement mRNA Nakamura neural plate neural tissue neural tube Nieuwkoop node normal notochord observed obtained occurs organizer origin pieces possible posterior prechordal present presumptive ectoderm primary principle problem produced prospective protein reaction region regulation reported roof secondary seems showed shown side somites specific Spemann stage stained streak structures studies substance suggested synthesis tail tested theory Tiedemann tion Toivonen transplanted Triturus trunk tube various vegetalizing ventral yolk