Download Lecture 1: Brief Outline:

Gastrulation V: A-P patterning
Reading: Gilbert: p. 343-346; p. 358-364.
Review Article: Endoderm Development: from patterning to organogenesis.
(2000) by A. Gapin-Botton & D. Melton. Trends in Genet. 16: p.124-130.
Gatstrulation, Part 5: Establishing Anterior-Posterior patterns
1. Review concept of organizers and responsive fields
- Initial cell movements of gastrulation establish axes that subsequently are
further divided by one population of cells signaling to another to modify local
gene expression.
- Further differentiation of the organizer: how it progresses from the
node/spemann organizer to a “head” and “tail” organizer.
-Feedback inhibition: how it might to establish boundaries: notch signaling
(contact mediated inhibition), agonist/antagonist signaling (e.g.Bmps/noggin), and
intracellular regulators of signal transduction (e.g.sprouty/fgfs; RA/Cyps).
-Ttranscription factors as effectors of morphogenetic signaling: mechanism by
which anterior-posterior identity is established.
-Gastrulation axes lead to organizing centers anteriorly as well as posteriorly:
these centers help set up orderly A-P expression of transcription factors that
establish morphogenetic domains.
- Comparison with drosophila: for vertebrates, especially mammals, the details are
quite different, and the role of cell-cell signaling is key.
2. Anterior/Posterior Signaling
-The idea of the anterior state as an initial “default”: is ectoderm also the initial
default?
-What are the posteriorizing signals: Fgfs, Wnts, RA, Bmps, Nodal
-What are the anteriorizing signals: antagonists of the posteriorizing signals
3. What are the targets of Anterior/Posterior Signaling
- Brachyury, Tbox genes
- Hox genes: anterior boundary of expression, regulation by RA,
colinearity/clusters, replication of a-p pattern in all three germ layers.
-What do Hox genes do? What are their targets and what happens when they are
disregulated by disrupted signals?
4. A-P Patterning in the endoderm and the development of a/p organization in the viscera
as an example of the axial consequences of late gastrulation a/p organization.
-overview of gut tube formation, representative of morphogenetic movements that
follow initial gastrulation and axis formation to facilitate organogenesis.
- introduction of differentiation along the gut tube: a-p axis formation as a guide
for regional and cellular specification/diversity.
-signaling in the gut: local emergence of organizing centers that reinforce a-p
organization established during late gastrulation
-transcription factor codes in the gut for a-p specification: do they predict identity
and are they functioning in a “homeotic” fashion to influence differentiation
program of entire a-p localized cell classes?
5. Discussion of paper: “Establishment of intestinal identity and epithelial/mesenchymal
signaling by Cdx2.” (2009) N. Gao, P. White, and K.H. Kaestner, Dev. Cell 16: 588-599.