Lecture 15- Neural crest I Flashcards
When does the neural crest arise and what types of animals have it?
- arises early in development
- it is transient
- occurs only in vertebrates
What types of cells arise from the neural crest cells? (in general only)
- yields range of cell types including bone, connective tissue, endocrine cells, melanocytes, neurons, glial cells
- the neural crest cells are responsible for the formation of the jaw, parts of the ear, PNS and ANS, turtle shell, teeth come from neural crest plus endothelial cells
What are some examples of birth defects that arise due to problems in neural crest development?
- Treacher Collins Syndrome: single mutation of a gene which results in lot of the neural crest cells that form the face dying so get abnormally structured face and bones of the face
- Hirschsprung’s disease: a disorder of the abdomen that occurs when part or all of the large intestine or antecedent parts of the gastrointestinal tract have no nerves and therefore cannot function, the neural crest cells migrating into the colon to create the ENS fail to reach the end bit and the gut is not functional, lethal if not treated (need surgery)
- In mouse mutants no face forms when neural crest cells fail to migrate properly
What is the neural crest derived from?
- ectoderm
- the neural crest cells are cells that migrate away from the dorsal lips of the neural groove and neural tube
When does the neural crest form?
- at around the same time as that neural induction and neurulation occurs
- neural crest cells become specified during that time and by the time the neural tube fully closes they are separated from the ectoderm and ready for migration
What are the 5 steps in neural crest formation and “life”?
- Induction of neural plate border
- Specification of the neural crest (happens during neurulation)
- Epithelial-Mesenchymal transition (change from epithelial cell type to mesenchymal migratory cell type)
- Migration
- Differentiation
What are the 3 phases of neural crest life we are discussing in this lecture? (the first 3)
- Induction of neural plate and neural plate border: BMPs and BMP antagonists intermediate levels of BMPs Wnts and FGF induce it
- Onset of neural crest specification, induction of cells with neural crest potential: BMPs, Wnts and neural plate border genes induce “neural crest specifier genes” (eg. Snail. Sox10 and FoxD3)
- EMT (Epithelial-Mesenchymal transition) and neural crest emigration: Cadherins, matrix metalloproteases etc. Important roles for BMP and Wnt together with neural crest specifier genes
What genes/proteins are involved in the induction of neural plate and neural plate border?
-BMPs and BMP antagonists intermediate levels of BMPs Wnts and FGF induce it
What genes/proteins are involved in the onset of neural crest specification, induction of cells with neural crest potential?
-BMPs, Wnts and neural plate border genes induce “neural crest specifier genes” (eg. Snail. Sox10 and FoxD3)
What genes/proteins are involved in the EMT (Epithelial-Mesenchymal transition) and neural crest emigration?
-cadherins, matrix metalloproteases etc. Important roles for BMP and Wnt together with neural crest specifier genes
What is the first step in the neural crest induction?
- establishment of the neural plate border
- the border region of the neural plate is prevented from becoming epidermis or neural plate via expression of particular genes (PAX7, PAX3, Msx, Zic)
picture: yellow is the neural plate border
What establishes the neural plate border?
- intermediate levels of BMP with Wnt and FGF (need all those components to turn on the neural plate border genes)
- Wnt and FGF drive the expression of the neural plate border genes PAX3/7, Msx, Zic
- Wnt and FGF are coming from the mesoderm, Wnt also comes from the ectoderm
What happens when the region with intermediate BMP levels is expanded?
- the neural plate border expands
- knocking out BMP entirely does not have this effect, only intermediate levels of BMP do
- can reduce BMP levels in one half of the embryo thus have an internal control
- the region expressing PAX3 and other neural border genes is larger
(Xenopus model)
How does BMP level affect what type of tissue forms in the embryo?
- regions with low BMP= neural plate
- intermediate BMP= neural plate border
- high BMP= ectoderm
Is intermediate level of BMP sufficient to get formation of neural plate border?
- no, not sufficient to get expression of neural plate border genes (PAX3/7, Msx,Zic)
- when animal cap was cultured with intermediate BMP levels only, no neural plate border genes were expressed
What else is needed for neural border gene expression apart from intermediate BMP levels?
- Wnt and FGF
- it is enough to have just one (either Wnt or FGF) and get expression of neural plate border genes (PAX3/7, Msx, Zic)
What transcription factors are expressed at the neural plate border?
- PAX3
- PAX7
- Msx
- Zic
- the neural plate border is marked by these and their expression is regulated by BMP, Wnt and FGF signalling
- expression of the PAX3/7, Msx, Zic differes spatially but together they form the neural plate border
What process follows neural crest induction?
-neural crest specification
When does neural crest specification occur?
-during neurulation
What happens to the embryo if you block expression of neural plate border genes?
- it prevents neural crest specification
- here tested it using morpholinos
- injected into left side of the embryo so have internal control
What happens when you have Pax3 or Zic1 in an animal cap assay alone, do you get FoxD3 expression?
-no
Do you get FoxD3 expression when you have Pax3+Wnt or Zic1+Wnt?
-yes
What is the relationship between the neural plate border genes Pax3 and Zic1, growth factor Wnt and neural crest specifier FoxD3?
- get expression of FoxD3 if you have Pax3+Wnt or Zic1+Wnt
- Wnt must turn on Pax3 or Zic1, depending on the mixture
- Wnt and the neural plate border genes (Pax3, Zic1) turn on expression of the neural crest specifier FoxD3
Diagram showing how neural plate genes and growth factors work together to specify neural crest:
What do you need to get extra strong expression of FoxD3?
Pax3, Zic, BMP and Wnt
Diagram connecting all the pathways:
- slide 29 in lecture neural crest I, look up for better deifnition
- what to take from this:
- there is more stuff going on than what we discuss
- all of these things in the same space and at similar times
- Msx1/2= turns FoxD3 on, so does Pax3/7 also but Zic only in trunk
What does loss of FoxD3 in the neural crest result in?
- loss of many neural crest derivative
- picture: FoxD3 mutants, missing cartilage and structure of face wrong
What is the state of the neural tube by the time EMT takes place?
-usually fused but depends on the species
EMT= epithelial to mesenchymal transformation
What are the differences betwen the properties of epithelial and mesenchymal cells?
Epithelial:
- organised cell layer
- cell-cell adhesion
- tight junctions and adherens junctions
- apical basal polarity (have bottom and top)
- associated with basal lamina
Mesenchymal:
- not organised cell layer
- lack tight junctions
- focal and transient contact with other cells
- different cell shape and organisation
- can be highly motile
What do epithelial and mesenchymal cells look like in culture?
-different shape
What are the connections between epithelial cells like?
- many connection to each other
- tight junction: composed of a branching network of sealing strands, strands are mostly made of Claudins (transmembrane proteins)
- adherens junction: more basal than tight junctions, cell junction whose cytoplasmic face is linked to the actin cytoskeleton, involve mostly Cadherins (transmembrane proteins)
- connections between the cytoskeletons of two cells, tightly bound
What is the connection between EMT and cancer metastasis?
- The changes during neural crest EMT are very similar to those in cancer metastasis.
- The neural crest EMT is used as a model for cancer.
What signals promote EMT?
- BMP and Wnt together with neural crest specifier genes promote EMT
- BMP is in ectoderm and dorsal part of the neural tube
Is BMP important for neural crest specification and EMT?
- yes
- if take out the intermediate parte of the neural tube= doesn’t become neural crest on its own
- does when add ectoderm= get neural crest
- or can add BMP 4 or 7 and get neural crest
-demonstrates that BMP is important for EMT and for neural crest specification
What were the experiments with BMP and its effect on EMT in chick trunk neural crest?
- if you add Noggin (BMP inhibitor) then the cells don’t migrate
- if add BMP4 then the whole neural tube becomes neural crest= so BMP specifies the neural crest and makes neural crest cells migratory
- if have Noggin, that inhibits BMP expression in dorsal neural crest= and no migration
- BMP and noggin interaction determines the timing the EMT (via rostral caudal wave)
- noggin at first expressed but decreases over time in a rostral to caudal direction
What is the relationship between neural crest specifier genes and migratory genes?
- neural crest specifier genes regulate expression (e.g. Snail2) of migratory genes
- sntisense oligonucleotides to knock down the neural crest specifier Snail2 (Slug) prevents neural crest cells from migrating
- snail genes repress particular cadherins (E-cadherin and Cadherin-6B), genes required for tight junctions and regulate other genes required for EMT.
Diagram connecting all the genes and factors in this lecture:
-
Diagram showing transmembrane proteins and their targets:
-do not have to memorize just to have an idea of the complexity involved
What are some additional things that moderare/regulate cell fate?
The action of transcription factors and control of transcriptional state is modified by multiple factors:
- chromatin remodelling
- post-translational modification of proteins
- post-transcriptional modifications (role of miRNA)
- other signalling pathways
