Developmental biologists did the following experiments to discover the role of e

Question

Developmental biologists did the following experiments to discover the role of endoderm in the specification of cardiogenic mesoderm. Using early mouse embryos: Experiment 1: Removed the anterior endoderm and cultured the embryo - no cardiogenic mesoderm and no heart muscle cells developed. Experiment 2: Removed anterior endoderm and replaced it posterior endoderm from another embryo and cultured the embryo - no cardiogenic mesoderm and no heart muscle cells formed. Experiment 3: Removed anterior endoderm and replaced it anterior endoderm from another embryo and cultured the embryo - cardiogenic mesoderm and heart muscle cells developed. Interpret these data. What are the signals that come from the anterior endoderm? What is their role in specification of the cardiogenic mesoderm?

Explanation / Answer

Experiment 1 indicates that anterior endoderm somehow signals/induces the mesoderm to develop into cardiac tissue

Experiment 2 suggests that signals from anterior endoderm are specific to it i.e. conditioned positionally and hence cannot be complemented by the posterior endoderm.

Experiment 3 confirms the above hypothesis which was deduced from experiment 1. Signals from the anterior endoderm are conserved across individuals of the species and can complement each other.

Signals coming from the anterior endoderm are majorly secretary ligands which induce specific signalling cascade inside the mesoderm causing them to acquire cardiac cell fates. Some of these signals are FGF8,Shh, Crescent, BMP2. They are known to induce certain cardiogenic transcription factors in the neighboring mesoderm.

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