[Inducing capacity of subcellular fractions from the gastrula ofXenopus laevis]

Isolated yolk platelets, nuclei and pigment granules, ribosomes and the ribosome-free supernatant of homogenates from whole gastrulae ofXenopus laevis were tested for their inducing properties.The subcellular fractions were obtained by differential centrifugation in sucrose media and their purity was checked by electronmicroscopy.The microsomal fraction shows archencephalic and deuterencephalic inducing capacity which is enhanced after extraction with pyrophosphate and with phenol. The membrane structures of this fraction can partially be separated from the ribosomes by treatment with desoxycholate. Proteins with deuterencephalic and spinocaudal inducing activity are extractable from the desoxycholate treated microsomal fraction with 1 M NH₄Cl.The supernatant, free of ribosomes, has a rather weak inducing ability. After extraction with phenol the archencephalic and deuterencephalic activity increases, but not the spinoaudal.Isolated nuclei induce small deuterencephalic structures and a relatively high percentage of spinocaudal differentiations. Extraction with phenol does not enhance the rate of these inductions.The yolk platelets show mainly deuterencephalic inducing activity which is associated essentially with the superficial layer of these particles. Proteins, inducing archencephalic and deuterencephalic tissue differentiations, are extractable in small amounts from the platelets after partial removal of the superficial layer.