Vertebrate eye development Flashcards
Which factors determine the early eye field?
Pax6, Rx and Six3
The separation of the single eye field domain to two bilateral eye fields depends on what?
Shh
Where does Shh come from and what does it repress?
Comes from the prechordal mesoderm and floor plate
Suppresses Pax6/Rx expression in the centre of the embryo
Mutations in Shh can cause what?
Cyclopia - a single eye in the centre of the face, below the nose
What is holoprosencephaly?
A failure of the ventral forebrain to form as a result of a Shh mutation
When do the eyes begin to form in gestation?
3 to 7 weeks
What are the steps when the eye begins to form?
1) The eye field grows sideways and contacts the ectoderm
2) The ectoderm thickens forming a placode
3) The eye field forms a double layered cup
The optic vesicle will contain what?
The neural tissue ie neurons and the retina
The thickened placode will form what?
The lens
How do primary optic vesicles arise?
From the frontal eye fields as an evagination of neural epithelium at the 5 vesicle stage
What connects the optic vesicle to the diencephalon?
The optic stalk which will become the optic nerve
List what arises from
a) Neural ectoderm
b) Surface ectoderm
c) Migrating cells
a) retina and retinal pigment epithelium
b) the lens
c) Sclera and the anterior chamber
In humans when does eye devlopment start and end?
E22 begins
Finishes several months after birth
Induction of the optic vesicles is the first of what?
Reciprocal inductive interactions
What happens once the optic placodes have been induced?
The lens placode signals back to the optic vesicle = morphological transformation
It invaginates and forms a two layered cup like structure
How does the lens form from the lens placode form?
The lens placode invaginates, pinches off and forms a hollow ball of cells
They are stem cell like
Lens cells make lots of which protein and why?
Crystallin - it is transparent
What happens once a lens cell has produced crystallin?
It throws out its nucleus
Describe the layers of the optic cup
Outer layer = retinal pigment epithelium
Inner later = inner neural epithelium
Retinal progenitor cells are found where?
The inner layer and outer layer
What do inner retinal progenitor cells form?
Ganglion cells, bipolar, amacrine cells, photorecptors and muller ganglia
What is the retinal pigment epithelia?
Pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells
What do outer retinal progenitor cells form?
Pigmented cells = eye colour ie through melanin
Describe what happens when the optic cup folds
The inner wall of the cup becomes neural retina
The outer wall becomes the pigment epithelium
What is the molecular mechanism of generating neurons in the retina?
Master transcription factors are used - these can induce ectopic eyes if misexpressed
What are the eye master transcription factors?
Pax 6, Six 3, Rx1
Describe interkinetic migration in the neural tube
When cells are dividing the nuclie move:
- G1 and S phase = necleus away from the lumen
- M phase and cytokinesis = close to the lumen
What happens at cytokinesis?
The lateral attachment is lost and then reforms
How can radial glia cells divide?
Asymetrically - one cell will differentiate in to a neuron
How do daughter cells from radial glia migrate away from the ventricular zone?
They use scaffolding provided by the mother
What are the nueroblastic layers outside to in?
Out = rods and cones Middle = Bipolar cells Inner = ganglion cells
How can we know that neuroblasts are stem/ progenitor cells?
A virus containing B-galactosidase is injected into the back of a rat eye to infect precursor cells
After 4 - 6 weeks the eye is removed and stained for the presence of B-galactosidase
Stained cells form a strip across the neural retina = five rods, one bipolar neuron, a rod terminal and five muller glial cells
