Neurulation Flashcards
derivatives of ectoderm
- results from neurulation and subsequent development
ectoderm structures : surface ectoderm
- epidermis
- lens, cornea
- anterior pituitary
ectoderm structures: neural crest
- peripheral nervous system
- facial cartilage
ectoderm structures: neural tube
- brain
- neural pituitary
- spinal cord
- retina
draw neural tube formation
–
neural tube formation
- cell shape and adhesion changes
- see figure
early shaping of neural tube
- morphological manifestation of segmentation in the development of the CNS
- 3 part to 5 part brain
- prosencephalon divides into telencephalon and diencephalon
- mesencephalon divides into myelen, meten and mesen.
telencephalon
- cerebrum
diencephalon
- optic vesicle
mesencephalon
- midbrain
metencephalon
- cerebellum
myelencephalon
- medulla
neuromeres
- the segments of the neural tube that establish the embryonic brain during development
neural tube formation and patterning
- gradient of BMP determines if ectoderm will be neural or not…
- low BMP = neural plate
- medium = neural border
- high BMP = non neural ectoderm
Neural induction
- BMP gradient
- BMP inhibits neural formation
- BMP antagonists inhibit BMP (chordin, noggin)
- draw figure
what does BMP do?
- blocks dorsal/neural development
- allows for ventral development
1st step to neural tube patterning
- wnt/ant-wnt gradient
- see figure (draw)
patterning AP axis
- AP identity of broad regions of CNS is specified during gastrulation and neural plate formation
- two signaling centers:
1: head organizing regions: Anterior visceral endoderm, prechordal plate
2: notochord
first step of patterning AP axis
- following neural induction, vertical inductions from signaling centers produce first subdivision
- defines midbrain-hindbrain borders
forebrain/midbrain region
- Otx2 TF is expressed
hindbrain/spinal cord region
Gbx2 TF is expressed
second step of patterning AP axis
- isthmic organizer (isthmus)
- expression boundary between otx2 and gbx2
- midbrain/hindbrain border
- controls regional specification of neural tissue
- FGF8 synthesized posterior to isthmus
- wnt1 synthesized anterior to isthmus
- leads to expression of engrailed
Third step patterning AP axis
- FGF8 and Wnt induce a gradient of expression of certain transcription factors on both sides of the isthmic organizer
- induces engrailed, which expresses Pax2 and Pax5
fourth step patterning AP axis
- Pax2/5 and pax6 TFs subdivide early neural tube into 3 divisions
- pax2 and 5 expressed in midbrain and rhombomere 1 region
- pax6 expressed in forebrain and hindbrain
- SEE FIGURE
Pax6
- master control gene
- development of eyes and sensory organs
fifth step of patterning AP axis
- forebrain/midbrain development
combo of patterning AP axis steps
- 1) vertical inductions produce 1st subdivisions
- 2) Isthmic organizer
- 3) FGF and Wnt induce TF gradient
- 4) Pax 2,5 and 6 divide early neural tube into 3 parts
- 5) Forebrain/ midbrain development
Posterior neural development
- caudal to the isthmic organizer; hindbrain and spinal cord
3 signaling pathways of posterior neural development
- Wnt
- FGF
- retinoic acid
Regulation of Posterior neural development
- response to graded signal
- differential thresholds of response to constant signal
- interactions of different pathways
- see figure
role of Wnt/B-catenin activity in posterior neural developement?
- caudalizes the embryonic nervous system
cascade gene expression, posterior neural development
- wnt activates cdx and meis
- cdx inhibits PG14 Hox (hindbrain), activates another hox (spinal cord)
- meis activates PG14 hox
- spinal cord hox inhibits hindbrain hox
- see figure
segmentation of hindbrain
- rhombomere formation
- involved expression of several categories of genes
- similar to drosophilia
segmentation of spinal cord
- defined by signals from paraxial mesoderm (somites)
- see figure
How do hox genes specify segmental identity
- Regulated by:
TFs acting on gene specific regulatory regions
gene position
miRNAs - not expressed in forebrain/midbrain
- important in hindbrain through spinal cord
- segmental identity of individual neuromeres
How are hox genes expressed
- temporal and spatial order
- reflects order on chromo
- sharp anterior border, less sharp posterior border
- 3’ genes required for production of anterior structures
- almost every region of AP axis characterized by Hox genes
