Patterning of the CNS Flashcards
Name the first three brain vesicles to form. Next, list what they differentiate into.
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
prosencephalon splits into:
- telencephalon
- diencephalon
mesencephalon remains as is
rhomencephalon splits into:
- metencephalon
- meyelencephalon
Which morphogens initiate A-P patterning? Include which end of the embryo they are secreted from.
Wnts, retinoic acids (RAs) and fibroblast growth factors (FGFs) are secreted from organisers at the posterior end of the embryo, whereas Wnt inhibitors Cerberus and Dickopf are secreted from organisers at the anterior end.
After the initial opposing morphogen gradient is set up for A-P patterning (Wnt inhibitors vs Wnts), different Wnt inhibitors are secreted at the anterior end to define additional boundaries. True or false?
True.
Briefly outline the events of the canonical Wnt signalling pathway in regions where high levels of Wnt are present (i.e. at the posterior end of the embryo).
- Wnt binds to its ligand (frizzled)
- B-catenin is translocated to nucleus where it binds to its cofactor
- transcription of target genes occurs
Briefly outline the events of the canonical Wnt signalling pathway in regions where Wnt inhibitors are present (i.e. at the anterior end of the embryo).
- Wnt binds to Wnt inhibitors (cannot bind to frizzled)
- B-catenin cannot be translocated to nucleus
- Wnt target genes are off
How are Hox genes important for development in verterbrates? What about for development of Drosophila?
Hox genes are necessary for a given rhombomere to become morphologically different from another in the hindbrain of vertebrates.
In Drosophila flies, Hox genes are necessary for a given body segment to become morphologically different from another.
How are Hox genes aligned on chromosomes?
Anterior to posterior order of gene expression is ordered in a 3’ to 5’ order on the chromosomes.
I.e. the anterior most expressed gene is 3’ and the posterior most expressed gene is 5’.
Are Hox genes highly conserved across species?
Yes.
At late gastrula/early neural plate stages in the embryo, two genes are expressed in domains adjacent to one another. These genes mediate a fundamental division of the CNS. Name the two genes and outline where their expression extends to and from.
otx2 expression determines forebrain and midbrain (expressed from anterior end of embryo to mes-met border).
gbx2 expression determines hindbrain and spinal cord (expressed from mes-met border to posterior end of embryo).
The mes-met border is also known as the _______ ________.
Isthmic Organizer.
otx2 and gbx2 genes set up the initial distinction between the anterior and posterior of the embryonic nervous system. At the boundary between these two genes, the mes-met border forms and morphogens are expressed. Name the morphogens and their collective role.
Fgf8, en1 and Wnt1. These morphogens act in a regulatory network to maintain their expression and refine the mes-met boundary.
The mes-met border is a _________ organizer.
secondary organizer.
The mes-met border, along with two other secondary organizers, divide the brain into three major regions (forebrain, midbrain and hindbrain). True or false?
True.
Transplantation of Isthmic Organiser into developing forebrain regions results in…? Which transcription factor is responsible for this?
An ectopic midbrain-hindbrain boundary due to Fgf8 expression.
What are the primary organizers responsible for patterning along the D-V axis? Distinguish dorsal from ventral and name which morphogens they secrete.
Dorsally, the overlying ectoderm secretes BMPs, FGF and Wnts. Ventrally, the notochord secretes Shh.
