In the avian embryo, the Area Pellucida (AP) becomes polarized along its posterior-anterior axis by a directional cell shading during the intra uterine stages. This polarity is at later stages superimposed upon the blastoderm by sequential polarized morphogenetic processes. Along the years experiments were done to learn mostly about the importance of the posterior region of the blastoderm to initiate a single posterior anterior embryonic axis, but never to check the tendencies of the polarized AP to form the axis. In this work an attempt was done to determine whether the polarity of the AP has a developmental potential to initiate the embryonic axis and if it is independent of the strong inducing activity of other regions of the blastoderm. Pieces of the posterior midline of the polarized AP were cut out and replaced with reverse polarity. In other cases, the posterior midline region was exchanged with other regions of the AP and both pieces were reverse transplanted. In most cases the majority of reversed pieces changed their original polarity and the primitive streak formed from a point adjacent to the original polarity of the blastoderm. Therefore, it is concluded that the polarized AP is not sufficient by itself to determine the polarity of the avian embryonic axis.
Buy this Article