LECTURE 8: development of sense organs

Question 1

where can sensory neurons in vertebrates originate from?

Answer 1

• neural crest
• neural tube
• placodes

Question 2

in the development of the AP axis, which region does the eye field occupy?

Answer 2

a lot of the ventral part of the anterior neural plate

Question 3

how is the eyefield split into 2 bilateral regions?

Answer 3

1. specialised TFs expressed in the ventral part of the anterior neural tube characterise the early eye field
2. prechordal mesoderm secretes Shh and induces Shh expressing ventral midline cells
3. downregulation of eye field genes –> eye field split into 2 bilateral regions

Question 4

the retina is a specialised outgrowth of the ________ _______

Answer 4

ventral forebrain

Question 5

Describe how the process of eye formation from the eye field

Answer 5

1. eye field grows sideways. optic groove becomes optic vesicle
2. outgrowing optic vesicle contacts surface ectoderm - ectoderm thickens to form an optic placode
3. optic vesicle forms a u shaped structure then a cup shaped structure
4. placode invaginates + pinches off to form a circle of cells
   cup shaped structure gives rise to the retina
   circle of cells gives rise to lens
5. results in lens surrounded by double layered optic cup

Question 6

the optic vesicle buckles to form an optic double layered cup consisting of an inner layer and an outer layer. what do these layers give rise to?

Answer 6

outer layer - retinal pigment epithelium which produces melanin
inner layer - neuroepithelium/stem-like population

Question 7

Neuroepithelium/stem-like population of the inner layer

Answer 7

• self-renews - builds up progenitor pool

- progenitors differentiate to give rise to ganglion cells, interneurons, photoreceptor cells etc.

Question 8

Aniridia

Answer 8

Disease caused by mutant Pax6 in humans

Question 9

Pax6

Answer 9

• ‘master eye’ transcription factor conserved throughout evolution
• ectopic expression induces ectopic eyes
• expression usually restricted to optic vesicles

Question 10

Where are the progenitors of the neurons of the retina located?

Answer 10

Outer neuroblastic layer of the inner layer of the optic vesicle

Question 11

describe the waves of retinal cells that form during the building up of the sensory retina

Answer 11

6-7 weeks = 1st wave —> ganglion cells
7-8 weeks = 2nd wave —-> bipolar cells
8-9 weeks = 3rd wave —-> rods and cones

Question 12

where are most placodes derived from?

Answer 12

neural plate border region at top end

Question 13

DEFINE: placodes

Answer 13

specialised areas that initially form as regions of thickened epithelium that give rise to particular structures containing sensory cells

Question 14

Where does the neurogenic region lie in the forming otic vesicle?

Answer 14

base

Question 15

what are the cranial placodes?

Answer 15

olfactory placode
lens placode
trigeminal placode
ear placode

Question 16

describe the formation of the ear

Answer 16

1. thickening induced otic placode formation
2. otic placode folds to form a pit
3. pit pinches off to form otic vesicle
4. otic vesicle forms ear