The Role and Control of WNT Signalling in an HESC Model of Human Primitive Streak
type: CreativeWork
description: In amniotes, gastrulation is marked by the creation of the primitive streak (PS) and is largely controlled by WNT, BMP, and ACTIVIN/NODAL signalling. Despite detailed characterization in model organisms, the human PS and the role these pathways play in its formation and patterning remains a mystery. In this work I focused on understanding the role and control of the WNT pathway in human PS development. Due to the ethical limitations of working with human embryos, I used an in vitro human embryonic stem cell (hESC) micropatterned "gastruloid" system. I first showed that in the human PS there is a conserved BMP → WNT→ NODAL signalling initiation hierarchy, and that WNT is necessary and sufficient for PS formation. Next, I found that structured subpopulations of endoderm and mesoderm emerge and self-organize depending on different BMP, WNT, and ACTIVIN/NODAL levels, and that by comparison to the mouse embryo I could arrange these subpopulations along an anterior-posterior axis. With the development of a new cell tracking technique, I was also able to identify and characterize robust cell migrations from the PS region of each gastruloid that depended on which fates the cells would ultimately adopt. Putting these pieces together, I was able to derive a rudimentary first fate map of the human PS, as well as a rough picture of the BMP, WNT, and ACTIVIN/NODAL signalling gradients that determine it. One interesting and unforeseen result from this fate map was the hint of a human "organizer" cell fate that emerged under joint WNT and ACTIVIN/NODAL stimulation. To characterize and functionally prove this organizer's existence, I devised an ex ovo cross-species transplantation strategy grafting treated gastruloids into chick embryos. The assay demonstrated that the human cells induce and contribute autonomously to a secondary axis while inducing neural fate in the host, thus fulfilling the most stringent criteria for an organizer. This work adds an important milestone to the re…
abstract: In amniotes, gastrulation is marked by the creation of the primitive streak (PS) and is largely controlled by WNT, BMP, and ACTIVIN/NODAL signalling. Despite detailed characterization in model organisms, the human PS and the role these pathways play in its formation and patterning remains a mystery. In this work I focused on understanding the role and control of the WNT pathway in human PS development. Due to the ethical limitations of working with human embryos, I used an in vitro human embryonic stem cell (hESC) micropatterned "gastruloid" system. I first showed that in the human PS there is a conserved BMP → WNT→ NODAL signalling initiation hierarchy, and that WNT is necessary and sufficient for PS formation. Next, I found that structured subpopulations of endoderm and mesoderm emerge and self-organize depending on different BMP, WNT, and ACTIVIN/NODAL levels, and that by comparison to the mouse embryo I could arrange these subpopulations along an anterior-posterior axis. With the development of a new cell tracking technique, I was also able to identify and characterize robust cell migrations from the PS region of each gastruloid that depended on which fates the cells would ultimately adopt. Putting these pieces together, I was able to derive a rudimentary first fate map of the human PS, as well as a rough picture of the BMP, WNT, and ACTIVIN/NODAL signalling gradients that determine it. One interesting and unforeseen result from this fate map was the hint of a human "organizer" cell fate that emerged under joint WNT and ACTIVIN/NODAL stimulation. To characterize and functionally prove this organizer's existence, I devised an ex ovo cross-species transplantation strategy grafting treated gastruloids into chick embryos. The assay demonstrated that the human cells induce and contribute autonomously to a secondary axis while inducing neural fate in the host, thus fulfilling the most stringent criteria for an organizer. This work adds an important milestone to the re…
author: Martyn, Iain
keywords: primitive streak, human gastrulation, Wnt signaling, hESC gastruloids, organizer, DKK1/E-cadherin feedback, Life Sciences
date published: 2019-01-01T08:00:00Z
date modified: 2026-07-24T04:11:28Z
provider: Rockefeller
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Rockefeller