Question

Describe transplantation experiments in chick that showed the importance of Henson’s node and the posterior marginal zone

Answer 1

• 1930- Conrad Hal Waddington

Invented a technique to grow the embryo of chick on plasma clots. By this method he removed the Henson's node and placed in another area. He observed that notochord, somites and neural tubes are developed in new location and it suggest that the Henson's node control the axis formation and related structural growth.

Further studies on gene expression discovered that there are two sets of gene expression in Henson's node.The first genes are expressed in posterior part of Koller's sickle and second in anterior part of primitive streaks. From this Koller's sickle the primitive streaks and anterior-posterior axis will form.

• 1993- Takayuki Inagaki , Gary C Schoenwolf

They conducted an experiment to observe the axis formation in avian embryos. In the first group the quail embryos are transplanted to chick embryo and the structure developed from grafted nodes were analysed. The grafted node self differentiated appropriate for their stages and the embryo of host developed as normal. The axis developed from grafted tissue merged caudally with host structures .

In second group Henson's node from quail embryo were placed lateral to the node of chick embryo. A single axis is developed with graft node self differentiating the specific structures and it merged caudally with host structures.

In the third group the ability of Henson's node to organize ectopic embryo was analysed by transplanting to extra embryonic germ cell crescent . In this central one third of embryo is transplanted and still the exotic embryos developed. This indicate that a portion of Henson's node also has the ability to develop.

This experiment conclude that Henson's node is self-differentiating.