L5 - Brain and Spinal Cord Flashcards
Different parts of the nervous system
CNS, PNS, ENS
Are all formed in embryogenesis arising from the neural plate
The main different parts begin to be established early in embryogenesis – 3-5 weeks in humans
What is tagging?
In early embryos specific molecules can be tagged
This reveals organisation, regionalisation and development of specific regions that prefigure and predict later adult parts
Neural tube is regionalised along the anterior-posterior axis in the embryo so that the early neural tube cells form either brain/brain derived structures or spinal cord
Positioning of axial mesendoderm
Anterior endoderm/prechordal mesoderm lie under one end of the neural plate – anterior
Notochord lies under the other end of the neural plate
As organiser begins to differentiate into axial mesoderm it?
Involutes
Undergoes convergent extension
Extends under the midline of the newly induced neural plate
Signals from the axial mesendoderm
The signals are different to signals from notochord
Signals act on overlying neural plate cells to induce anterior or posterior transcription factors
Extension of the neural plate -activation transformation model
Signals from notochord cause cells at the back of the neural plate to proliferate
At the same time other signals from notochord transform these cells from an anterior to a posterior identity
- Turn of the transcription factors that dictate anterior identity
- Turn on transcription factors that dictate posterior identity
Activation transformation model
It is the basis for formation of forebrain (anterior) verses hindbrain and spinal cord (posterior)
Regional pattern established by?
Placing two antagonistic molecules at each end of a growing structure
Pattern establishment - signals from prechordal mesoderm
Organiser upregulates BMP antagonists
- Chordin, noggin which are maintained in the prechordal mesoderm
At same time Wnt antagonists induced
Pattern establishment - signals from notochord
Anterior end – Wnt and BMP antagonists maintained
Posterior end – upregulation of Wnt, FGF and retinoic acid
Gradient of these along posterior/anterior axis
- Highest expression in posterior region
- Promote growth and posteriorize
Retinoic acid
Can diffuse through the membrane and bind to cytoplasmic receptor
When bound it can get through pores in nucleus and directly bind to promotors of genes to upregulate their transcription
Nervous system segmentation
Segmented along the AP axis
- Worms
- Insect larvae
Transforming gradient into step like units
Segmentation models
Alan Turing reaction diffusion model
Lewis Wolpert positional information French flag model
- As you get further from the source the concentration drops
- Cells can respond to particular threshold concentrations of the molecule
What do Hox genes control?
Larvae segmental identity
- Expressed in segmented patterns along the AP axis
- Evolutionary conserved
- First evidence for homology between invertebrates and vertebrates
What does homeobox DNA encode?
A DNA binding protein domain of 60 amino acids – homeodomain
Different domains of hindbrain and spinal cord are defined through Hox signature
Retinoic acid gradient induces different patterns of Hox transcription
