Vertebrate eye development

Question 1

Which factors determine the early eye field?

Answer 1

Pax6, Rx and Six3

Question 2

The separation of the single eye field domain to two bilateral eye fields depends on what?

Answer 2

Shh

Question 3

Where does Shh come from and what does it repress?

Answer 3

Comes from the prechordal mesoderm and floor plate

Suppresses Pax6/Rx expression in the centre of the embryo

Question 4

Mutations in Shh can cause what?

Answer 4

Cyclopia - a single eye in the centre of the face, below the nose

Question 5

What is holoprosencephaly?

Answer 5

A failure of the ventral forebrain to form as a result of a Shh mutation

Question 6

When do the eyes begin to form in gestation?

Answer 6

3 to 7 weeks

Question 7

What are the steps when the eye begins to form?

Answer 7

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

Question 8

The optic vesicle will contain what?

Answer 8

The neural tissue ie neurons and the retina

Question 9

The thickened placode will form what?

Answer 9

The lens

Question 10

How do primary optic vesicles arise?

Answer 10

From the frontal eye fields as an evagination of neural epithelium at the 5 vesicle stage

Question 11

What connects the optic vesicle to the diencephalon?

Answer 11

The optic stalk which will become the optic nerve

Question 12

List what arises from

a) Neural ectoderm
b) Surface ectoderm
c) Migrating cells

Answer 12

a) retina and retinal pigment epithelium
b) the lens
c) Sclera and the anterior chamber

Question 13

In humans when does eye devlopment start and end?

Answer 13

E22 begins

Finishes several months after birth

Question 14

Induction of the optic vesicles is the first of what?

Answer 14

Reciprocal inductive interactions

Question 15

What happens once the optic placodes have been induced?

Answer 15

The lens placode signals back to the optic vesicle = morphological transformation
It invaginates and forms a two layered cup like structure

Question 16

How does the lens form from the lens placode form?

Answer 16

The lens placode invaginates, pinches off and forms a hollow ball of cells
They are stem cell like

Question 17

Lens cells make lots of which protein and why?

Answer 17

Crystallin - it is transparent

Question 18

What happens once a lens cell has produced crystallin?

Answer 18

It throws out its nucleus

Question 19

Describe the layers of the optic cup

Answer 19

Outer layer = retinal pigment epithelium

Inner later = inner neural epithelium

Question 20

Retinal progenitor cells are found where?

Answer 20

The inner layer and outer layer

Question 21

What do inner retinal progenitor cells form?

Answer 21

Ganglion cells, bipolar, amacrine cells, photorecptors and muller ganglia

Question 22

What is the retinal pigment epithelia?

Answer 22

Pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells

Question 23

What do outer retinal progenitor cells form?

Answer 23

Pigmented cells = eye colour ie through melanin

Question 24

Describe what happens when the optic cup folds

Answer 24

The inner wall of the cup becomes neural retina

The outer wall becomes the pigment epithelium

Question 25

What is the molecular mechanism of generating neurons in the retina?

Answer 25

Master transcription factors are used - these can induce ectopic eyes if misexpressed

Question 26

What are the eye master transcription factors?

Answer 26

Pax 6, Six 3, Rx1

Question 27

Describe interkinetic migration in the neural tube

Answer 27

When cells are dividing the nuclie move:

• G1 and S phase = necleus away from the lumen
• M phase and cytokinesis = close to the lumen

Question 28

What happens at cytokinesis?

Answer 28

The lateral attachment is lost and then reforms

Question 29

How can radial glia cells divide?

Answer 29

Asymetrically - one cell will differentiate in to a neuron

Question 30

How do daughter cells from radial glia migrate away from the ventricular zone?

Answer 30

They use scaffolding provided by the mother

Question 31

What are the nueroblastic layers outside to in?

Answer 31

Out = rods and cones
Middle = Bipolar cells
Inner = ganglion cells

Question 32

How can we know that neuroblasts are stem/ progenitor cells?

Answer 32

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