Redefining the Gastrula Organiser in Early Chick Embryo Development
type: CreativeWork
description: The vertebrate organiser has, since its discovery in 1924, long been considered responsible for patterning the primary body axes and inducing the formation of the embryonic nervous system. Hensen’s node was identified as the equivalent structure in birds due to its ability to induce a complete secondary axis with a regionalised neural tube when grafted to an ectopic location. The node also demonstrates extraordinary regenerative capacity: following surgical ablation, it can completely regenerate, and normal development follows. Previous observations suggest that a developmental delay occurs following organiser ablation, in both chick and frog embryos. We performed single cell RNA sequencing on node-ablated and control chick embryos during the first 5h post-ablation, to investigate any potential associated changes. Regeneration occurred rapidly, but even prior to this, the only differentially expressed genes were associated with the endoderm, reflecting the removal of the node as the source of endoderm cells. Many cells expressing organiser genes remained after ablation, confirmed with HCR staining and RT-qPCR, showing that organiser genes are expressed as a gradient from anterior to posterior along the primitive streak (PS). Grafting sections of the PS from different anteroposterior (AP) levels into host embryos showed that neural induction ability is not confined to the node, but is also distributed as an AP gradient along the PS. An ‘organisation field’ therefore exists in the chick embryo, rather than it being a unique property associated with one morphological structure. Node regeneration occurs through cells moving into the centre of the embryo and becoming respecified to acquire node identity. I asked how the rest of the embryo responds if the node is prevented from regenerating, by attempting to block these movements with a piece of area opaca tissue. This either led to the graft acquiring node identity, or regeneration occurring around the graft. As the node…
abstract: The vertebrate organiser has, since its discovery in 1924, long been considered responsible for patterning the primary body axes and inducing the formation of the embryonic nervous system. Hensen’s node was identified as the equivalent structure in birds due to its ability to induce a complete secondary axis with a regionalised neural tube when grafted to an ectopic location. The node also demonstrates extraordinary regenerative capacity: following surgical ablation, it can completely regenerate, and normal development follows. Previous observations suggest that a developmental delay occurs following organiser ablation, in both chick and frog embryos. We performed single cell RNA sequencing on node-ablated and control chick embryos during the first 5h post-ablation, to investigate any potential associated changes. Regeneration occurred rapidly, but even prior to this, the only differentially expressed genes were associated with the endoderm, reflecting the removal of the node as the source of endoderm cells. Many cells expressing organiser genes remained after ablation, confirmed with HCR staining and RT-qPCR, showing that organiser genes are expressed as a gradient from anterior to posterior along the primitive streak (PS). Grafting sections of the PS from different anteroposterior (AP) levels into host embryos showed that neural induction ability is not confined to the node, but is also distributed as an AP gradient along the PS. An ‘organisation field’ therefore exists in the chick embryo, rather than it being a unique property associated with one morphological structure. Node regeneration occurs through cells moving into the centre of the embryo and becoming respecified to acquire node identity. I asked how the rest of the embryo responds if the node is prevented from regenerating, by attempting to block these movements with a piece of area opaca tissue. This either led to the graft acquiring node identity, or regeneration occurring around the graft. As the node…
author: Neaverson, Alexandra
language: eng
keywords: brain, chick embryo, embryo development, hensen's node, neural development, organiser, regeneration
license: https://www.repository.cam.ac.uk/bitstreams/3042f916-24ad-41d0-a34c-b7a4589769e3/download
license: https://creativecommons.org/licenses/by/4.0/
date published: 2025-09-11
date modified: 2026-07-24T01:33:28Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.126648