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By using the quail-chicken chimera technique, we studied the reactivity and the eventual developmental or inducing capacities of the avian caudal marginal zone (in comparison with Rauber's sickle), when associated in vitro with different avian blastoderm components. If a fragment of quail sickle endoblast is placed on the caudal marginal zone of a whole unincubated chicken blastoderm, then a secondary miniature embryo will develop in this caudal marginal zone. The primitive streak and accompanying neural plate of the secondary embryo are directed peripherally into the caudal germ wall, away from Rauber's sickle. Thus, the 'mirror image development' indicates that the upper layer of the caudal marginal zone can react in the same way as the upper layer of the area centralis, because of the presence of sickle endoblast. A quail Rauber's sickle fragment placed on an isolated anti-sickle region always induces a primitive streak directed centrally. After prolonged culture, blood vessels and associated coelomic vesicles are formed. By contrast if a quail caudal marginal zone is placed on an isolated chicken anti-sickle region, the primitive streak, blood vessels and coelomic vesicles do not form. Thus, in contrast to the inducing effect of Rauber's sickle, the caudal marginal zone has no inducting effect by itself, even in the absence of the dominating effect of Rauber's sickle. [ABSTRACT FROM AUTHOR]

An upper layer (epiblast) fragment taken laterallyfrom the Anlage fields of neural plate or chordamesoderm of a quail blastoderm,labelled with [sub 3] H-glucosamine, was grafted isotopically (in a similarregion), isochronically (at the similar stage of development) and isotropically(with the same caudocranial and dorsoventral polarity) in the epiblast ofa mesoblast free area of a chicken blastoderm (St 4–5 Vakaet, 1970:full grown primitive streak). On the autoradiographs of the sections throughsuch cultured blastoderms with fully integrated quail grafts, we observeda labelling of the basement membrane laterally and slightly cranially fromthe labelled graft in its final position. Since only the epiblast and its basement membrane are involved, the pattern of the observed labelling indicatesthat the grafted and integrated quail epiblast fragment glides in toto over the mediocaudally localized basement membrane, leaving behind atrack of radioactivity. Sliding of whole groups of epiblast cells over thebasement membrane seems thus to be a normal phenomenon during avian gastrulation. [ABSTRACT FROM AUTHOR]

The developmental capacities of an avian germ (from before symmetrization to the moment of laying) are strongly diminished after inversion of its egg yolk ball followed by culture in egg white. Our present experiments show that even when the avian germ is completely horizontally inverted (without an upper or lower border) below its egg yolk ball before symmetrization, symmetrization and gastrulation phenomena take place. The germ grows slower and becomes smaller than after normal incubation. After culture of inverted unincubated germs, localized on freshly laid eggs, the closure of the neural tube is impaired and it remains open over a long distance. Although a primitive streak (PS) develops, mesoderm migration (mainly from the lateral part of the area pellucida) is also impaired. On sections through the germinal disc one can see the abnormal upward migration into the depth of the ooplasm and yolk of cells from the germ wall and the development of large cellular extensions encircling the yolk globules. Most prominent is the loss of contact between the superficial cell layers and the deep layer elements (junctional endoblast and yolk endoblast in the area opaca). Large areas without deep layer elements (even visible on surface micrographs) develop in the area vasculosa and area vitellina interna. The margin of overgrowth grows and extends normally over the egg yolk ball. An autoradiographic study after labelling of the yolk layers in inverted egg yolks reveals that mainly compression of the peripheral subgerminal and perigerminal ooplasm takes place. This suggests that the compression by the neighbouring yolk and upwards growth of cells are at the origin of the impaired development. After return to the normal upward orientation of the germ on the topmost part of the egg yolk ball, a more or less pronounced restoration to normal development takes place (depending on the duration of the inversion period and the age of the germ). [ABSTRACT FROM AUTHOR]

In the present study, we demonstrate that quailjunctional endoblast fragments have powerful embryo-inducing potencies whenplaced on the deep side of the upper layer (UL) of the anti-sickle regionof unincubated chicken blastoderms. Moreover, in most cases the inducing potenciesof the autochthonous Rauber's sickle-endophyll complex were inhibited at distance.Also, junctional endoblast still in situ in an early streak embryostrongly inhibits the inducing capacities of a Rauber's sickle – endophyllcomplex apposed on the deep side of the upper layer of the cranial part ofthe area pellucida. So junctional endoblast, besides embryo inducing potenciesalso seems to dominate and to inhibit at distance the gastrulation potenciesof an ectopically placed or autochthonous Rauber's sickle – endophyllcomplex. [ABSTRACT FROM AUTHOR]