An integrated experimental study of endoderm formation in avian embryos

Abstract

The formation of the endoderm during primitive streak stages in avian embryos was studied by combining several of the following techniques for each embryo. These included microsurgery, time-lapse filming, use of chick-quail chimaeras, tritiated thymidine autoradiography and a novel technique for identifying the morphology of the cells after small pieces of tissue from known areas had been maintained in culture for 24 h. Using these techniques we have confirmed that the ventral layer of the early chick embryo receives contributions from both the marginal and the central regions of the area pellucida. The former seems to consist of yolky cells derived from the germ wall, whilst the latter consists of smaller, less yolky cells derived from the more dorsal layers of the embryo. The movement of the lower layer anteriorly during these stages appears to be dependent upon mechanical constraints imposed upon it by the expanding tissue in more caudal regions. The extent of each of the two contributions to the lower layer was determined as a function of stage and presence or absence of a lower layer, and the findings are discussed in the light of the existing literature.

Determination of embryonic polarity in a regulative system: evidence for endogenous inhibitors acting sequentially during primitive streak formation in the chick embryo

“…Embryo manipulation was performed in Tyrode's solution (Stern and Ireland, 1981). Anterior halves were obtained by cutting embryos with a hair loop; the cut edge was then sealed by apposing a strip of outer area opaca from the anterior region of another embryo.…”

“…Anterior halves were obtained by cutting embryos with a hair loop; the cut edge was then sealed by apposing a strip of outer area opaca from the anterior region of another embryo. After manipulation, embryos were set up in modified New culture (New, 1955;Stern and Ireland, 1981). In situ hybridisation was carried out as previously described (Stern, 1998).…”

“…1A) (New, 1955;Stern and Ireland, 1981). The posterior half (where the streak normally forms) develops an axis in 93/98 (95%) cases, within the same time course as normal uncut embryos.…”

A balance of FGF, BMP and WNT signalling positions the future placode territory in the head

“…Host embryos were maintained in New Culture (Stern and Ireland, 1981) and grafts placed into the inner third of the area opaca. Quail nodes were excised from primitive streak stage embryos, while the neural plate, head and trunk mesoderm were dissected from stage 5-7 embryos using fine needles and 0.05 mg/ml dispase.…”

Regulation of programmed cell death during neural induction in the chick embryo

“…Eggs were incubated at 38 o C and staged according to Hamburger and Hamilton (1951). A modified version of the New technique was used to culture embryos (Stern and Ireland, 1981). Transplantation of Hensen's node was performed at stage 3+/4 as described previously (Stern, 1999, Storey et al, 1992.…”