Lecture 21

Question 1

Bride of sevenless and sevenless are two genes identified to be involved in the ability to Drosophila to perceive light. What is seen in sev and boss mutant flies

Answer 1

They will move to be in white light over UV light as opposed to the other way around as is seen in wild type

Question 2

What kind of experimental methods could be used to confirm the role of the transcription factors that specify formation of the eye fields

Answer 2

In situ hybridisation

Question 3

What is seen in mice with a homozygous mutation in the gene that specifies eye development

Answer 3

Small eyes

Question 4

Pax6, Rx and Six3 expression is maintained in the forming retina as well as in the early eye field. What is the role of this continued expression later in development

Answer 4

Important role in the balance of stem cells and differentiated cells

Question 5

Where do the axons of the outer photoreceptors (R1-R6) project to

Answer 5

The lamina

Question 6

If wnt signalling is used to induce expression of Pax6, Rx and Six3, what would you expect to be the results of an overexpression of frizzled and why

Answer 6

Frizzled is a wnt receptor and so overexpression of fz will lead to increase wnt signalling and a subsequent overexpression of the eye field specifying genes

Question 7

There are 2 layers to the optic cup consisting of inner neural epithelium and the outer retinal pigment epithelium. To what do these structures give rise to

Answer 7

The inner neural epithelium give rise to the ganglion, bipolar, amacrine and photoreceptor cells as well as the Muller glia. The outer pigmented epithelium give rise to the pigmented cells that give the eyes their colour

Question 8

What type of protein is boss

Answer 8

Bride of sevenless is a membrane-tethered ligand specific for sev

Question 9

What is the name of the EGF receptor ligand secreted by R8, 2 and 5 that leads to subsequent recruitment of cells

Answer 9

Spitz

Question 10

What structure of the eye is derived from the retina

Answer 10

Retina

Question 11

Which bHLH proneural gene is involved in a horizontal cell fate

Answer 11

Prox1

Question 12

The expression of which three transcription factors characterise the eye fields

Answer 12

Pax6, Six3 and Rx

Question 13

How are the R8 photoreceptors specified to form

Answer 13

Notch-delta signalling between the cells within the morphogenetic furrow acts as a lateral inhibition mechanism to space future R8 cells

Question 14

Explain how the lens or optic placode is induced

Answer 14

As the optic vesicles grows out is touches the adjacent surface ectoderm and induces a thickening of this tissue forming the optic placode

Question 15

Explain how the optic cup forms from the optic vesicle and lens placode

Answer 15

The lens placode invaginates with the optic vesicle to produce a double-layered cup structure referred to as the optic cup

Question 16

Using what you know about sonic hedgehog signalling governing the bilateral splitting of the early eye field, describe the effects of sonic hedgehog mutations on eye development

Answer 16

Mutations in the shh gene or inhibition of protein processing results in cyclopia. The phenotype results in a single eye in the centre of the face (and usually below the nose). This occurs to the failure of the early eye field to split and in humans leads to the condition holoprosencephaly. This is characterised by a Failure of the ventral forebrain to form and a failure of the pituitary as well as cyclopia, general problems within the midline of the face

Question 17

Flies with mutant R1, 2 and 3 wont develop R7 is R8 isnt present, T or F

Answer 17

T – having wild type R1, 2 and 3 is not sufficient to generate an R7

Question 18

Outline the process of interkinetic nuclear migration

Answer 18

As elsewhere in the developing CNS, proliferating cells undergo interkinetic nuclear migration. Cell division takes place at the lumen. During G1 cells migrate inward towards the lumen. They undergo S-phase at the inner surface and migrate outward in G. Cells that exit the cell cycle at the outer surface then migrate to their final location

Question 19

What are the two structures from which the major sensory organs of the head develop from

Answer 19

Anterior neural tube and the adjacent cranial ectoderm

Question 20

Wild type Drosophila are phototactic with a preference for UV light, what is seen in R7 mutants

Answer 20

They will go towards white (visible) light due to an inability to see UV light

Question 21

What is the name of the structure where the axons of the R7 and R8 neurons cross over

Answer 21

Optic chiasm

Question 22

What can be said about the cell division seen ahead of, within and behind the morphogenetic furrow

Answer 22

Ahead of the morphogenetic furrow the cells are dividing, within the furrow the cells have arrested in G1 of the cell cycle. Behind the morphogenetic furrow there is limited cell division

Question 23

Interactions between the parts of the anterior neural tube with the adjacent ectoderm results in a series of epidermal thickenings. What is the name given to this thickened region of ectoderm

Answer 23

Cranial ectodermal placode

Question 24

Th eye fields initially form as a single structure in the midline. Describe how development of the neural tube leads to the formation of two bilateral eye field structures

Answer 24

Prechordal mesoderm expresses sonic hedgehog in the midline. Cells in the midline are induced to form floor plate by sonic hedgehog signalling which forces the separation of the eye field. The floor plate itself pushes aside cells of the early eye field. Then Shh protein from the prechordal mesoderm and floor plate suppresses Pax6/Rx expression in the centre of the embryo, dividing the field in two

Question 25

Sev and boss genes can be removed from R1-6 without causing loss of R7 specification, T or F

Answer 25

T

Question 26

Cells of the optic stalk give rise to only one cell type, which cells are these

Answer 26

Astrocytes of the optic nerve

Question 27

What is the term used to describe the mechanism by which the optic placode and optic vesicle interact with each other to form the optic cup and lens

Answer 27

Reciprocal inductive interaction

Question 28

What is the term given to a gene that is both sufficient and necessary to dictate the formation of particular structures

Answer 28

Master regulatory genes

Question 29

How do the stem-like cells of the early lens differentiate

Answer 29

The cells of the lens elongate to form lens fibre cells

Question 30

What is the significance of using notch-delta signalling in lateral inhibition

Answer 30

Notch delta signalling uses transmembrane ligands which limits the distance over which it can act to a single cell diameter

Question 31

Homozygous mutants for Pax6 die perinatally with no eyes having developed, T or F

Answer 31

T

Question 32

Sev is absolutely required in R8, T or F

Answer 32

F – sevenless is absolutely required in R7, bride of sevenless is absolutely required in R8

Question 33

Many extrinsic signalling factors (including Shh, Notch, BMPs) govern differentiation of the different neuronal cell types found in the retina by inducing expression specific transcription factors that determine cell fate. Which bHLH proneural gene drive bipolar cell fate

Answer 33

Chx10

Question 34

How is the lens of the Drosophila eye formed

Answer 34

The cones cells of the ommatidia secrete the overlying lens

Question 35

In sensory organs, the neurons develop from the neural tube. From which structure do the specialised sensory organs such as the lens develop from

Answer 35

Placode

Question 36

Describe the cells of the mature lens

Answer 36

Lens fibre cells are long fibre-like cells that fill the inside of the lens. These cells are enucleate and transparent due to the production of a protein called crystallin

Question 37

Describe how interkinetic nuclear migration leads to the development of a layered retina

Answer 37

During G1 and S phase the nucleus is moving towards to the mantle zone away from the lumen. The nucleus then retracts to the lumen; the cell divides and its projection to the mantle zone is temporarily lost during M phase and cytokinesis. The two daughters produced are either retained as stem cells at the lumen or differentiate into neuron. The daughter that differentiates into a neuron migrates along its sister cell which has reformed its projection with to the mantle zone. The inner layer of optic cup contains the stem like population which is maintained. Closer to the forming lens neurons are built up creating a thickening of the retina.

Question 38

Six3, Rx and Pax6 are sufficient for eve development, T or F

Answer 38

T

Question 39

What is the name given to the two characteristic bulges that appear either side of the anterior neural tube at the start of eye development

Answer 39

Eye fields – these form the retina

Question 40

Describe briefly how the cornea forms after the lens

Answer 40

Once the lens has formed, another inductive interaction causes the surface ectoderm that has joined up where the lens vesicle invaginated to become the transparent cornea. This is under the influence of signals from the lens

Question 41

What is the phenotype of Rx and Pax6 heterozygotes

Answer 41

Small eyes

Question 42

What causes the appearance of the morphogenetic furrow

Answer 42

The morphogenetic furrow is caused by a shortening of the columnar epithelial cells

Question 43

Rx and Pax6 homozygotes have no eyes, T or F

Answer 43

T

Question 44

R6 and R1 are then recruited before R7 is specified last, T or F

Answer 44

T

Question 45

Pax6 has been determined to be both necessary and sufficient to dictate eye development, what is the experimental evidence for this in Drosophila

Answer 45

Misexpression of human Pax6 in Drosophila leads to the development of ectopic eyes throughout the fly

Question 46

Which cells of the ommatidia are the first to form

Answer 46

R8

Question 47

How does the lens form from the optic placode

Answer 47

As the optic vesicle invaginates to form the optic cup, the optic placode invaginates too. The concavity of the optic placode increases to the point where it pinches off from the overlying ectoderm and forms a spherical structure that will ultimately become the lens

Question 48

The cells that form the hollow ball of the early lens are a stem-like population. As well as self-renewing, what cells can they give rise to

Answer 48

Lens fibre cells

Question 49

Pax6, Rx and Six3 are extremely conserved genes. Describe the experimental evidence for this significant conservation

Answer 49

Insertion of the mouse Pax6 gene into the Drosophila genome and random activation leads to the development of Drosophila eyes from Pax6 positive cells

Question 50

Ectopic activation of Pax6, Rx and Six3 is sufficient to induce ectopic eye development, what can be inferred about these transcription factors

Answer 50

They are master regulatory genes governing eye development

Question 51

After the lens placode invaginates and pinches off, it forms a hollow ball of cells. What is the name given to this structure

Answer 51

Lens vesicle

Question 52

What structure connects the optic vesicle to the diencephalon and what will the structure later become

Answer 52

The optic stalk – will later become the optic nerve

Question 53

In which cell(s) of the ommatidia is boss expressed in

Answer 53

R8

Question 54

Two different cell types arise from the inner and outer layers of the optic cup, which specific fates are these and from which region are they derived

Answer 54

The retina will develop from the inner surface of the optic cup whereas the pigmented epithelium develops from the outer layer of the optic cup

Question 55

A balance of which anterior-posterior patterning signals lead to the positioning of the eye fields

Answer 55

Wnt signalling and wnt antagonists (FGF and RA)

Question 56

What type of protein is sevenless

Answer 56

RTK

Question 57

What is meant when in development of the eye it is said that neurons are born in waves over time

Answer 57

Essentially, the time of when stem cell generates a neuron will determine what that particular neuron is going to be

Question 58

With what you know about the cells of the mature lens, describe what cataracts are

Answer 58

Cataracts are a failure of the lens to make more lens fibre cells. As they are enucleate, they die within 6 weeks

Question 59

What is the significance of the equator that runs through the neurocrystalline lattice structure of the Drosophila eye

Answer 59

The equator is a line of mirror symmetry that runs through the centre of the eye where the R7 indents of each surrounding ommatidia is positioned so as to face it

Question 60

The anterior most regions of the neural tube forms the diencephalon, T or F

Answer 60

T

Question 61

The primary optic vesicles arise from the frontal eye fields as an evagination of the neural tube epithelium, T or F

Answer 61

T