Early interaction between deep and superficial layers in avian blastodiscs: uptake of ooplasmic determinants

Parts from radially symmetric prelaid quail blastodiscs placed in culture in contact with isolated cranial quadrants from unincubated chicken blastoderms induce in the chicken upper layer the formation of a miniature embryo with primitive streak and neural plate. Both components (blastodisc parts and upper layer fragments) do not differentiate into an embryo when cultured apart. We concluded that the fort-nation of the avian blastoderm is the result of an interaction between the deep part of the blastodisc and the uncommitted upper layer. Indeed during the culture period the deep part of the quail blastodisc differentiates into quail sickle endoblast and quail junctional endoblast, indicating the formation of Rauber's sickle material in the quail tissue which by induction gives rise to the development of an embryo in the neighbouring upper layer. The here observed induction phenomena result from placing early deep material on more advanced upper layer. This suggests an analogy with the phenomena observed after the eccentric, radially-symmetry-breaking displacement of the deep layer, with reference to the superficial layer which occurs during normal bilateral symmetrization under influence of gravity in undisturbed eggs in utero.