Dorsal lip

The dorsal lip of the blastopore is a structure that forms during early embryonic development and is important for its role in organizing the germ layers.

[3] The dorsal lip refers to the section of tissue located at the site of the first invagination in the developing pregastrula and is understood to act as both the neural inducer in the early embryo as well as the overall organizer of the entire body axis.

[6] Experiments to identify the genetic basis for neural induction were conducted by exposing Xenopus embryos to UV radiation, which causes them to develop with no head.

[8] Similar experiments in the lab of Dr. Edward DeRobertis identified that chordin cDNA could also induce a secondary axis, suggesting that there is redundancy in the genes that code for neural development.

This was a result of the work of Doug Melton and Ali Hemmati-Brivanlou, who were studying the function of activin, a signalling molecule that acts on TGF-β receptors.

Figure 1:  Mangold's dorsal lip transplant experiment in Xenopus demonstrated that a transplanted dorsal lip could induce the formation of a double axis in the new host embryo, solidifying the dorsal lip's sufficiency in neural induction (A).  Injection of extracted mRNA from the dorsal lip into irradiated Xenopus embryos rescued neural induction and overall development demonstrating there is a genetic basis of neural induction (B).  Establishment of cDNA libraries from extracted dorsal lip mRNA identified candidate genes that may be responsible for neural induction.  One such candidate gene, noggin, is sufficient for rescuing development of irradiated embryos when its mRNA is injected (C).