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Eye Development Flashcards

1
Q

all eyes across the animal kingdom fundamentally consist of 2 cell types…

A
  1. photoreceptors (light-detective cells)
  2. pigment cells (supports photoreceptors & prevent light scatter)
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2
Q

the ocelloid of dinoflagellates is considered the simplest eye - what three features does it consist of?

A
  1. high levels of rhodopsin (photoreceptor light-sensitive molecule)
  2. membrane-folding (forms a light-sensing structure)
  3. crystalline lens made of crystalline bodies (organelles that focus light/pigment cells)
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3
Q

what is Pax6?

A

highly conserved gene; master regulatory for eye development across the animal kingdom

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4
Q

what is the homologue of human Pax6 in Drosophila? what does this show about eye development?

A

(homologue) eyeless - high conservation shows that though eyes between species show morphological diversity, their development & basic eye structure is fundamentally the same
- must have photoreceptors and pigment cells (light-detective and light-sensitive/supportive cells)

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5
Q

what is the homologue gene of human Pax6 in Drosophila?

A

Eyeless

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6
Q

in cross-species implantation of Pax6 from a mouse to non-eye tissues of fruit flies, ectopic eye formation was discovered. what is the significance of this?

A

demonstrates the high conservation of Pax6 as a master regulator of eye development - essential for eye development

can induce ectopic eye development in non-eye tissues

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7
Q

what is the difference between Pax6 and Rx in eye development?

A

Pax6 - universally essential in eye formation as a master regulator of eye fate
Rx - more species-specific (essential in vertebrates) to induce the eye field

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8
Q

function of Rx?

A

induction of eye field

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9
Q

in chronological order (relatively), what are the 5 steps in morphogenic eye development?

A
  1. eye field specification
  2. optic vesicle evagination
  3. optic vesicle patterning
  4. optic cup folding
  5. retina & retinal pigmented epithelium differentiation
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10
Q

what two components of the eye have neural derivatives?

A

retina & RPE - derived from neural tube; have connections to the brain

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11
Q

importance of the retina in visual processing?

A

retina has neural derivatives - has connections to the brain

retina has photoreceptors in outermost layer > visual info through neuronal cells > optic nerve > to brain via optic stalk

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12
Q

importance of the RPE in eye development?

A

provides trophic support to retina

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13
Q

examples of eye structures with non-neural derivatives - what do they mainly do?

A

e.g. lens & cornea (from surface ectoderm); blood vessels, eye muscles (from mesoderm)

important in protection & function of eyes

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14
Q

what is the eye field? where does it form, what does it give rise to?

A

eye field = specified region in the anterior neural plate early on in development (forms during neurulation) - gives rise to retina, RPE, optic stalk

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15
Q

what defines the eye field region in the anterior neural plate?

A
  • co-expression of eye field transcription factors (EFTFs) like Pax6, Rx, Tbx2
  • Otx expression in anterior neural plate during AP patterning
  • anterior signals blocking posteriorizing signals (e.g. Wnts, FGFs, RA) during neurulation = promotes anterior fates like eye field
    combination/co-expression of all these signals at the right time & place during development = specification of eye field in specific region of anterior neural plate
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16
Q

Why is Otx important for eye field specification?

A

Otx (TF) is expressed in anterior neural plate/ anterior regions; Gbx is expressed in posterior neural plate

mutual repression between Otx & Gbx confers distinct anterior neural plate identity - important for eye field specification in this region

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17
Q

what are eye field transcription factors (EFTFs)?

A

TFs that promote eye field specification - regulate downstream genes that confer eye fate to anterior neural plate genes

18
Q

examples of eye field transcription factors (EFTFs)?

A

Pax6
Rx
Tbx3
Six3/6

19
Q

difference between intrinsic & inductive developmental events?

A

intrinsic = external signals from one tissue influence the development of another tissue

inductive = internal genetic programs within a tissue drive its own development

20
Q

what is the role of Shh in splitting the eye field into bilateral optic vesicles?

A

specified eye region is a continuous region in the anterior neural plate - Shh is secreted from the ventral midline of this region
- represses Pax6 at the midline = prevents eye formation there
- splits the eye field into two lateral domains for two optic vesicles = two eyes

21
Q

what would happen if Shh expressed failed at the ventral midline during the splitting of the eye field into bilateral optic vesicles?

A

no Shh in ventral midline = no Pax6 repression = eye field wouldn’t split - potential for midline eye defects

22
Q

Q: considering eye field specification - give an example of intrinsic vs inductive events

A

intrinsic
- eye field transcription factors specifying eye fate through co-expression
- Otx expression defining anterior identity (esp. for eye field in the anterior neural plate) (mutual repression with Gbx - posterior-conferring TF)

inductive
- Shh signalling from ventral midline of continuous eye field represses Pax6 = drives splitting eye field & bilateral optic vesicles

23
Q

when does optic vesicle evagination begin in relation to neurulation?

A

begins before neural tube fully closes; during neurulation

24
Q

what are optic vesicles? where do they come from?

A

bilateral outpouchings of neuroepithelial cells- come form anterior neural plate, originate from specified eye field

25
what cell movements drive optic vesicle evagination?
outpouchings of neuroepithelial cells initially form bulges - begin moving towards each other at dorsal midline dorsal-ventral compressions force eye field cells to move laterally - form lateral evaginations of optic grooves that become optic vesicles
26
what's the role of the surface ectoderm during evagination?
surface ectoderm comes into close contact neuroepithelium of optic vesicle - reciprocal signalling promotes: - lens placode formation > lens vesicle - differentiation of neuroepithelial cells into retina, RPE & optic stalk (neural-derived eye structures) - optic cup folding of optic vesicle
27
what does the surface ectoderm induce in response to contact with the optic vesicle (neuroepithelium)?
lens placode > later forms lens vesicle
28
what occurs during the process of optic vesicle evagination?
occurs during neurulation; once eye field has been specified in anterior neural plate region - neural plate region consists of surface ectoderm & neuroepithelial cells - outpouching of neuroepithelial cells on either side of surface ectoderm move towards each other at dorsal midline - dorsal-ventral compressions of neural plate force evagination of eye field cells - form optic grooves > become optic vesicles as they evaginate laterally - end up with optic vesicle in close contact with surface ectoderm
29
what does the proximal region of the optic vesicle give rise to?
**optic stalk** - connects developing eye to the brain; guides retinal ganglion cell axons to form the optic nerve
30
what establishes proximal identity in the optic vesicle?
- Shh signalling secreted from ventral midline (notochord & floor plate) - induces TFs (e.g. Pax2, Vax1, Vax2) = define optic stalk region - Shh represses Pax6 in the proximal domain = helps define distinct boundaries between proximal/ optic stalk and distal/ neuroretina regions
31
how is distal (neuroretina) identity established in the optic vesicle?
FGFs from overlying surface ectoderm to distal optic vesicle (neuroepithelial cells) - induce Vsx2 expression, in combination with Pax6 expressed in distal regions = promotes neuroretina fate - neuroretina later thickens, invaginates - forms inner layer of optic cup (distal inner layer of optic cup = neuroretina)
32
what transcription factors are essential for conferring proximal/ optic stalk fate?
Pax2 (and Vax 1 & 2) - induced by Shh signalling from ventral midline Pax2 & Pax6 also exhibit mutual repression - confers distinct proximal/ optic stalk identity and sharp tissue boundaries
33
what part does the distal inner layer of the optic vesicle become? what signals specify this fate?
neuroretina - specified by FGFs from overlying surface ectoderm - induce Vsx2 (in combination with Pax6 already expressed in distal region) - confers neuroretina fate
34
what signals promote RPE fate over neuroretina fate in the distal region of the optic vesicle?
RPE fate: - Wnt signalling from extraocular mesenchyme > upregulates Otx2 and Mitf in distal outer/future RPE layer neuroretina fate: - FGFs from overlying surface ectoderm > induce Vsx2 (+ Pax6 already exp.) > confers neuroretina fate in distal inner layer - Vsx2 (retina) and Mitf (RPE) repress each other to prevent fate mixing between retina and RPE
35
what maintains the boundary between proximal & distal domains of the optic vesicle?
proximal = Pax2 distal = Pax6 - Pax2 and 6 mutually repress each other = maintains sharp border between optic stalk and neuroretina & RPE cells
36
why is mutual repression between Pax2 and Pax6 important in the optic vesicle?
establishes a clear boundary between proximal/ optic stalk & distal structures (neuroretina, RPE) - prevents fate mixing, proper regional identity in developing eye
37
how would loss of Shh affect PD patterning of the optic vesicle?
no Shh from ventral midline (notochord + floor plate) = no Pax2, Vax1, Vax 2 - no Pax2 = no repression of Pax6 keeping it in distal region - pax6 may expand abnormally over to proximal region - affects eye field cell fates = disrupt retinal vs optic stalk boundaries; affect optic stalk formation - further effects on tissue architecture = affects optic nerve
38
what outcome might result from ectopic FGF signalling in the optic vesicle?
- ectopic FGF signalling from overlying surface ectoderm - expanded Vsx2 expression - expanded neuroretinal fate; limited RPE fate/domain
39
FGF signalling from the overlying surface ectoderm to the distal optic vesicle specifies which fate?
specifies neural retina - FGF signals > induces Vsx2 & in combination with already exp/ Pax6 > neuroretina fate in distal outer layer of optic vesicle
40
what key tissue interaction drives further morphogenesis after optic vesicle evagination?
close contact between the optic vesicle and the surface ectoderm - leads to reciprocal signalling - induces the lens placode; promotes optic cup formation; differentiation of retina, RPE and optic stalk
41

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