Prof.Placzec Flashcards
Marysias First half of lecs
What is medulloblastoma and what does it lead to?
- Type of cancer
-Tumour in cerebellum - Affects coordinated motion
What is the role of a developmental neurobiologist?
Try and categorise neurons by working out how they are born from earlier cells looking at pre-cursors and genes and molecules affecting differentiation
What is a blastocyst?
Ball of cells
What happens to the blastocyst between weeks 3 and 4 of embryonic development?
Turned in to something with recognisable shape with the anterior portion eventually forming the brain and the posterior portion forming the spinal cord
What can be seen at weeks 4-5 of embryonic development?
Early brain and spinal cord cells
What is the solution to it being unethical to study embryonic development in humans?
- Studying on other vertebrates such as mice
- Processes essential to life such as sensory detection and breathing and are conserved throughout vertebrate evolution so its generalisable
What is a multipotent cell
Capable of giving rise to every cell + entirety of nervous system
What is the cell differentiation journey?
- Progressive process with successive proliferation changes
1. Induction (multipotent cells)
2. Regionalisation ( Pre-cursor cells)
3. Differentiation (One final neural fate)
What mediates the first break in symmetry
(multipotent cells->regionalisation)
Extrinsic signals
What are transcription factors?
Proteins made by the cell that act within the cell to upregulate the expression of other genes within the cell (intrinsic signal e.g.)
What is lost as you go through differentiation?
Potency
What are characteristics of Neural-like stem cells (multipotent)?
Express genes that regulate multipotent state
E.g. slow cell cycle/ stopping differentiation
What are characteristics of pre-cursor/progenitor cells?
Express genes that regulate faster cell cycle
Code for proteins that direct particular differentiation paths
What are characteristics of commited, differentiated cells?
Express genes that regulate cell cycle
Enable terminal differentiation
How are extrinsic signals received by early embryonic cells?
An ‘undecided’ early cell receives chemical signals from a neighbour, they alter the receiving cell
The receiving cell has to have the receptor for this chemical signal in order to change
How are intrinsic signals used in embryonic cells?
- Later on during differentiation
- Intrinsic information is already in the cell and can provide a ‘memory’ and ‘instruction’ for further fate specification
- Transcription factors
Give the analogy for a loss of function study
A girl wants to be x when she grows up, will she still become x if you remove etc. her teachers or her family or her friends (one by one)
Give the analogy for a gain of function study
Replacing/adding so for example if it was the teachers that influenced the girl to become x, if we take the teachers and put them in a school teaching another girl, will she want to become x as well
What are the two ways to conduct a loss of function study?
Background: Cell A produces a protein (an extrinsic signal) which morphs Cell B into Cell E
- Ablate cell A (which produces protein x), If B stays as B and does not become cell E, conclude that cell A required to cause cell E fate
- Prevent protein x through ‘mopping it up’, ‘degrading it’ or knocking out the gene which encodes for it. If B stays as B then the protein x is required for the change to cell E
What are the 4 ways to conduct a gain of function study?
Background: Cell C is further from Cell A and would not normally respond to the signal to change into cell E despite it having the complementary receptors
1. Take cell A from donor and put it in unusual location so proteins can reach cell C
2. Soak bead in protein X and transplant bead next to cell C to observe change to Cell E
3. Put the gene that encodes for protein X in another cell near to cell C
4. Add receptors for protein X to a cell with no receptors, observe to see if its the protein X signalling pathway responsible for change to Cell E
What are Ectoderm cells?
- One of the three germ layers
- The cells will proliferate and give rise to either the neural stem cells or epidermal cells
- Requires a Bone Morphogenetic Signalling Pathway to do so (BMP)
Describe the BMP signalling pathway
- Bone morphogenetic proteins are secreted signals
- When they bind their receptors (BMPR), they trigger a signal transduction cascade in the responding cell including second messengers
- As a result, Smad proteins in the cytosplasm are phosphorylated, enter the nucleus and act as ‘transcription factors’ that alter the gene expression
Where did our understanding of neural induction come from and how is it different to human neural induction?
- Came from amphibians
- They have a ‘sphere’ in terms of germ layers and we have a flat set of germ layers essentially as if the sphere was squashed
What are the three germ layers?
Ectoderm, Mesoderm, Endoderm
These three sub populations will always be arrayed in the same spatial context
What are Dorsal mesoderm cells or ‘organiser cells’
- A group of cells on one side of the mesoderm
- Produce Chordin, Noggin and Follystatin which block the BMP pathway
What is an organiser cell referred to as in a human?
Nodes
Which of the two fates of the ectoderm cells occurs in the ectoderm cells that are closest to the dorsal mesoderm cells?
Neural stem cells
How do Chordin, Noggin and Follystatin work?
- Antagonizers of BMPs
- Bind to BMPs or receptors which blocks the pathway
- Allow transcriptional profiling in nerual stem cell genes, ‘inhibitor of inhibitor is used to create positive effect’
Describe the molecular pathway for the decision of ectoderm cells to neural/epidermis
If ectoderm cells see BMPs, Smad proteins are phosphorylated, go into nucleus and bind to target genes allowing the cell to undergo an epidermal fate
In the absence of BMP signalling, Chordin, noggin etc. bind to the BMP and they prevent it from binding to its receptor meaning Smad proteins aren’t phosphorylated so its inactive, transcription factors such as Sox genes are activated and differentiation into a neural stem cell occurs
How does a fate map work?
stick dye into an early embryo, let it develop and see what cells did the early embryo give rise to
How was a fate map used to see if its the ectoderm closest to the dorsal mesoderm cells that gives rise to the neural plate?
- The specialised bit of the mesoderm is morphologically distinct to all the other parts of the sphere
- Stick a tracer into different sections of the ectoderm (dye) and see where all the cells end up so they could see that the ectoderm cells closest to the dorsal mesoderm cells made up the neural stem cells eventually
How was a gain of function experiment used to see if it is the mesoderm cells that are important in adjusting adjacent ectoderm cells to become neural?
- Two different strains of newts: white newts and dark newts
- From one white newt (e.g.) specialised mesoderm cells were taken out and transplanted to the other side of the embryo from the dorsal mesoderm in the dark coloured newt
- This embryo is now developing with two specialised mesoderm regions
- Two nervous systems were induced!!!! Showing that it is the organiser cells which induce the ectoderm cells to become neural
How was a GOF experiment used to see if its the BMP antagonists that are responsible for inducing neural tissue?
- Specialised mesoderm cells were taken out of an embryo and they were dissociated to single cells and the nucleus was shattered
- All mRNA from the organiser cell was extracted and reverse transcribed to make cDNA
- Each of those cDNA one by one was put in the opposite side of the mesoderm and expressed
- In this way it was identified which mRNAs were coding for a molecule that can induce neural identity
- The molecules that were able to alter the fate of the overlying ectoderm and tell them to become neural tissue were all antagonists of BMP signalling
What was in-situ hybridisation used for in figuring all of this out?
- Used to look at whether proteins are being expressed in the right places you know like is Sox2 being rightfully expressed near the organiser cells or is chordin being expressed at the dorsal mesoderm cells
- Can be used to study protein expression over time
What is neurulation?
Formulation of neural tube from a flat neural plate
What does morphogenesis mean?
Changing shape
What happens immediately after the neural plate is induced?
- It grows and elongates in lateral aspects (anterior posterior axis) and rolls into the neural tube in a term called neurulation
- The tips fuse, forming a neural tube
What is gastrulation?
The process which transforms the embryo from a one-dimensional layer of cells into a multi-layered embryo in which the adult body plan is recognisable
What happens during gastrulation and what is it driven by?
- Driven by organiser cells
- During gastrulation the germ layers assume their final positions and the anterior, posterior, dorsal and ventral axes become obvious
What transcription factors found in the organiser cells are responsible for gastrulation?
- Siamois and goosecoid
What does Siamois and Goosecoid do?
- Act within the organiser cells and bind to enhancers and promoters of genes (including BMP antagonists)
- Bind to a whole load of genes that direct their next step (dictate their own fate) which is differentiating and undergoing convergent extension
What is convergent extension?
Process by which a group of cells ‘squash’ together with nowhere to go meaning a blob of cells turns into a long thin rod of cells
What happens when the cells undergo convergent extension?
- More genes are turned on telling the cells to involute and moves under the midline of the induced neural plate
What is the ‘rod of cells’ called
The axial mesoderm
What is the axial mesoderm comprised of?
- Leading edge cells
- Pre caudal mesoderm cells
- Notocord cells
What does it mean for the cells if the neural plate is a single cell epithelium?
- That the cells are polarised
What does the band of F-actin at the apical domain of the neural plate do?
Pulls tight causing the cells to constrict at the edge causing a change in shape, neural tube formation
