Inductive interactions (wk 5) Flashcards
Which type of cell specification is typical of insects?
Synctial
Which type of cell specification is typical of invertebrates?
Autonomous
Conditional specification is typical of what type of organism?
Vertebrates (and some invertebrates)
Which two molecules form a gradient within a single cell during syntical formation?
bicoid and nanos
In mosaic development, can cells change their fate if a blastomere is lost?
No
What type of development does conditional specification give rise to?
Regulative development
What factor is important during conditional specification?
Position
Based on interactions with its environment
Mosaic development relies on ______ where as regulative development relies on ______
Mosaic= importance of segregation of determinants Regulative= importance of inductive interactions
T/F:
Taking a cell that would normally rise to ICM in mammals and move it to the outside it will form ICM on the outside of the blastocyst
False
if you get to it early enough you can move the cell to the outside and it will now become trophoblast cells
What is the ectoplacental cone?
Pre-cursor to the placenta
Which cells invade the uterine wall and what do they eventually form?
Synctiotrophoblast cells invade
They form the ectoplacental cone which is the pre-cursor for the placenta
Distinguish between the polar and mural trophoblast
Polar= closest to the ICM Mural= furthest away from the ICM
T/F:
Mural trophoblast attaches to the uterine wall
False
Polar trophoblast does
What happened when they removed the mural trophoblast cells and inserted ICM cells within it?
ICM had an effect on the mural trophoblast cells
Ectoplacental cone started forming which doesn’t happen in normal situations
__ cell sends an ____ signal to the ____ cell
Inducer cell sends an inductive signal to the responsive cell
T/F:
Morphogens are insoluble molecules
False
Soluble
What are the three types of ways cells can interact with each other?
Diffusion
Matrix
Direct
Distinguish between instructive and permissive inductive interactions
Instructive
- The underlying tissue provides a specific signal to the overlying tissue
- Type of underlying tissue is important to achieve the desired differentiated tissue
Permissive
- The tissue underneath provides a general signal, doesn’t have to be specific to get the desired differentiated tissue
What are the two important factors needed for any inductive interaction?
- The nature and presentation of the inductive signal
2. The competence of the responding tissue
Which process causes the ectoderm to differentiate into two different tissues? What are the two tissues?
Neuralation
Epidermal ectoderm
Neuroectoderm
Where does the neural groove arise?
At the primitive streak
List some things that the epidermal ectoderm and neuroectoderm give rise to
epidermal ectoderm gives rise to skin (epidermis), lens, inner ear, hair, nails, mammary glands
neuroectoderm gives rise to neural tube (CNS; brain, retina, nervous system) neural crest cells -cranial and sensory ganglia, head mesenchyme
T/F:
Epidermal ectoderm pinches off to form the optic vesicle
False
Neuroectoderm
How does the lens placode form?
Optic vesicle (vagination of the neural tube) makes contact with the overlying epidermal ectoderm Epidermal ectoderm responds and thickens
T/F:
Lens placode is thickened neuroectoderm
False
Thickened epidermal ectoderm
How does the optic vesicle become the optic cup?
Lens placode starts to invaginate and form the lens pit which causes the optic vesicle to collapse and eventually form the optic cup
What role does Shh play in eye development?
Ensures that two optic vesicles form
Knockout= only one forms
Cyclocephaly-cyclopia
(nasal prominence is also missing)
T/F:
Lens vesicle forms when the lens pit pinches off from the epidermal ectoderm
True
T/F:
Optic cup forms the cornea
False
Optic cup forms the retina
Overlying epidermal ectoderm (overlying the lens vesicle) forms the cornea
What are the primary fibres and where do they form?
They are the cells facing the developing retina (optic cup)
They are elongating
What does the optic stalk form?
The optic nerve
If you move the optic vesicle to another epidermal ectoderm what happens?
Lens placode can’t form because the ectoderm is not competent
What is the double assurance hypothesis
Notice a lentoid structure forming when the optic vesicle was not present
Concluded that the lens would normally arise by contact with the optic vesicle, but failing this, could arise separately if necessary
What three things is the head lens ectoderm exposed t during embryogenesis?
Presumptive pharyngeal endoderm
Presumptive heart mesoderm
Optic Vesicle
What are the primary induces that will establish competence and lens bias of ectoderm?
Endoderm (future pharynx)
Mesoderm(future heart)
What is the secondary inducer that initiates lens morphogenesis
Optic vesicle (future retina)
T/F:
Primary fibres have Pax 6 switched off
True
List one thing that differentiates lens epithelium and lens primary fibres
Primary fibres do not contain Pax 6 but lens epithelium does
T/F:
Pax 6 is not present in the optic cup
False
What happens when you knock out pax 6?
Nasal plate/nose is deformed
No eye forms
T/F:
Surface ectoderm requires expression of Pax6 in order to respond to the inductive optic vesicle
True
What produces solutes that populates the aqueous to provide nutrients and growth factors for the ocular environment?
Cillary body and Iris
Where is the proliferative hot spot for lens epithelial cells?
Germinal zone
Where do the lens epithelial cells start to become cuboidal and elongate into secondary fibre cells to allow the lens to grow?
Transition zone
What makes the lens transparent?
Crystallins
T/F:
Alpha crystallin is present in epithelial and fibre cells
True
T/F:
Beta and gamma crystallin is present in epithelial cells
False
Only present in fibre cells
How are the deeper layers of lens cells organised?
Ball and socket joints
- lose their smooth borders
- stick together using the ball and socket
- Important structural feature
How are the fibres of the centre of the lens organised?
More disorganised than the secondary fibre cells
What shape are the lens cells and why?
Hexagonal shape
Really efficient way of packing
Prevents the scattering of light
Why are ball and socket interactions necessary?
The cillary body has zonula fibres attached to the lens which moves the lens –> this movement can cause the fibre cells to slide to it is important there is structural strength
T/F:
When the cillary body muscle relaxes the lens will flatten
True
What comprises 95% of the tissue volume of the lens?
Fibre cells
What happens at the lens suture?
Elongating fibre cells arc around the lens equator, fibre tips will converge at the lens poles where they interlock to form the suture
What structural feature can be seen on the superficial lens fibres that confers structural stability?
Interlocking edge protusions between cells
What is degraded in the fibre cells near the centre of the lens to provide optical clarity?
Organelles
Here it is the organelle free zone
What is the shape of the suture? Why?
Y shape
Allows more cells to meet at a common point
What are the epithelial cells bathed in?
Aqueous
T/F:
The aqueous contains something that causes the epithelial cells to differentiate into fibre cells
False
It is the vitreous that is causing the differentiation
T/F:
FGF (fibroblast growth factor) induces epithelial cells to elongate and become fibre cells
True
T/F:
Lens epithelial cells gain pax6 and connexin43 when FGF is added
False
They lose it
List some things that occur when lens epithelial cells are exposed to FGF
Differentiate into fibre cells
Downregulate Pas6 and connexin43
Elongate
Induct beta and gamma crystalins, connexin 50 (communication), filensin, phakinin
Induces denucleation and ball and socket joints
T/F:
All ocular tissues including the lens express various types of FGF
True
T/F:
FGF is expressed only in the Vitreous
False
Also expressed in the Aqueous but the epithelial cells don’t have the right receptor here and won’t respond to it
T/F:
If lens epithelial cells express a small dose of FGF they will differentiate
False
Small dose= only proliferate
Need a large dose to differentiate
T/F:
Vitreous contains higher concentrations of FGF than the aqueous therefore cells exposed to the vitreous will differentiate and those exposed to the aqueous wont
True
T/F:
More FGF is located anteriorly compared to posteriorly
False
Other way round
Gradient from anterior to posterior
What is the role of TGFbeta?
Induces epithelial mesenchymal transition in cataract and posterior capsule opacification (secondary cataract)
What is a cataract?
Any opacification of the lens
What type of response is seen in a cataract?
Fibrotic response
Cells flatten and overlap
Contain particular cytoskeleton proteins not normally produced
TGFbeta induces the fibrosis
When exposed to TGFbeta, what type of cytoskeletal protein is expressed?
alpha smooth muscle actin (alpha SMA)
T/F:
Exposure to TGFbeta causes the production of ECM components such as laminin, HSPG, collagen I and III, fibronectin, tenascin
True
Where can you see EMT in adults?
Wound healing
Cancer metastasis
Fibrotic pathologies
What is PCO?
Posterior Capsule Opacificaiton is a long term complication with cataract surgery
Lens cells grow on the posterior capsule, modify the proteins as well, can produce wrinkling
