L9 - Development of Sense Organs

Question 1

Sensory neurons develop from different areas

Answer 1

Neural crest – e.g. sensory neurones of DRG
Neural tube – e.g. retina
Placodes – e.g. otic placode

Question 2

Where is the eye field set up?

Answer 2

In the anterior neural plate and borders ectoderm

Question 3

Eye-field growth between 3-7 weeks

Answer 3

Eye field grow sideways and contact ectoderm
Ectoderm contacted by outgrowing neural tube/optic grooves thickens – optic placode
- This pinches off to form a circle of cells – lens
Eye fields/optic vesicle form double layered cup – retina

Question 4

Optic cup differentiation - outer layer cells

Answer 4

Retinal pigment epithelium

Produce melanin

Question 5

Optic cup differentiation - inner layer cells

Answer 5

Stem like population which can either

• Self-renew
• Differentiate to ganglion cells, interneurons, light sensitive photoreceptor cells in the neural retina

Question 6

Retinal differentiation mechanism

Answer 6

Studies showed it is possible to induce ectopic eyes by ectopically activating transcription factors that are normally restricted to optic vesicles
=- E.g. Pax6
These master eye transcription factors have been conserved throughout evolution

Question 7

Layers of neurones in the retina

Answer 7

Build up layers of differentiated neurones while retaining a progenitor in the ventricular zone
- Same principles as in the spinal cord

Question 8

Where are the neuronal progenitors in the retina?

Answer 8

In the neuroblastic layer

Question 9

Waves of differentiated cells form 5 week

Answer 9

5 weeks - no differentiation
6 weeks – first wave of neurones – neuroblasts begin to divide asymmetrically
7 weeks – second wave of neurones
8 weeks – third wave of neurones

Question 10

The time of the wave of neuroblast differentiation dictates?

Answer 10

The type of neuron formed

Question 11

1st wave

Answer 11

Rods and cones

Question 12

2nd wave

Answer 12

Bipolar neurones

Question 13

3rd wave

Answer 13

Ganglion cells

Question 14

Vertebrate eye

Answer 14

Retina is a laminar structure
- Different layers as cells produced at different times
Sensory neurons derived from neural ectoderm

Question 15

Eye development requires function of which gene?

Answer 15

The Pax-6 gene

Question 16

Placodal origin of ear, lens and olfactory epithelium

Answer 16

Similar to sensory neuron origins (e.g. neural crest derived)
Placodes are derived from the same neural plate border

Question 17

Neural plate border is crucial for?

Answer 17

Head placodes – top end

Neural crest formation (peripheral nervous system development) – side

Question 18

Cranial placodes development

Answer 18

Circles show specialised thickened areas that have formed in the neural plate border
Give rise to the cranial placodes 
- Olfactory 
- Lens 
- Trigeminal 
- Otic

Question 19

Further development of cranial placodes

Answer 19

Ear develops from the otic placode
- Folds to give a pit
- Pinches off to a vesicle which then grows out
- Depending where a cell is in that vesicle it will assume different fates
Neurogenic regions - in the base of the vesicle
Sensory component come from this