Fate mapping the neural plate and the intraembryonic mesoblast in the upper layer of the chicken blastoderm with xenografting and time-lapse videography

The disposition of the Anlage fields of the neural plate and the intraembryonic mesoblast in the upper layer of the chicken blastoderm was studied at the primitive streak stage prior to the regression of Hensen's node (stages 5V to 6V, L. Vakaet (1970) Arch. Biol. 81, 387–426). Chicken blastoderms were cultured by New's technique on a mixture of thin egg white and agar. The anterior half of the deep layer was reflected with a tungsten needle. A circular fragment of the upper layer was punched out with a pulled out Pasteur pipette and discarded. It was replaced with an isotopic and isopolar piece of quail upper layer that was punched out with the same pipette. The deep layer was replaced and the chimeras were reincubated for 24 hours. The xenografts were followed with time-lapse videography. After fixation, the quail cells were located using Le Douarin's quail nucleolar marker technique. Integrating the observations with time-lapse videography and the results of Feulgen stained sections, we have drawn a new fate map of the disposition of the Anlage fields in the upper layer of the chicken blastoderm at stages prior to the regression of Hensen's node (stages 5V to 6V). The disposition of the neural plate and of the notochord, somites, nephrotome and lateral plates was therefore determined before the Anlage fields are morphologically discernible. The pathway of the fields in the upper layer towards their disposition was documented with time-lapse videography in chimeric chicken blastoderms that developed normally.