Determining the timeline of germ layer formation in zebrafish in a primer for “Reduced Expression of the Nodal co-receptor Oep causes loss of mesendodermal competence in zebrafish”
Hannah Campbell
Abstract
Background: The development of distinct germ layers is a vital part of vertebrateembryonic development. Nodal signaling is responsible for forming and maintaining mesendoderm. Mesendoderm is cell tissue found in zebrafish that will give rise to mesoderm and endoderm germ layers. In order for ectoderm to form, competence to Nodal needs to be lost. This primer investigates the developmental stage at which cells lose responsiveness to Nodal, and what is responsible for the loss of Nodal competence. Results: Injection of Nodal into embryos at different developmental stages demonstrated that prospective ectoderm loses responsiveness to Nodal at 75% epiboly. Activin A, a ligand that signals through the same receptors as Nodal, but does not require co-receptor Oep, was injected to determine what is responsible for the loss of competence. Activin A was able to induce mesendodermal markers in the prospective ectoderm at 75% epiboly as well as earlier stages. Oep injection along with recombinant human Nodal (rhNodal) was able to extend the window of competence. This suggests that Oep is the missing factor.
Conclusion: The experiments show that the loss of competence in the prospective ectoderm is a relatively simple cell-autonomous mechanism. Due to the upstream receptors in the pathway, this mechanism ensures a global effect.
