Lecture 21 Flashcards
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
They will move to be in white light over UV light as opposed to the other way around as is seen in wild type
What kind of experimental methods could be used to confirm the role of the transcription factors that specify formation of the eye fields
In situ hybridisation
What is seen in mice with a homozygous mutation in the gene that specifies eye development
Small eyes
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
Important role in the balance of stem cells and differentiated cells
Where do the axons of the outer photoreceptors (R1-R6) project to
The lamina
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
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
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
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
What type of protein is boss
Bride of sevenless is a membrane-tethered ligand specific for sev
What is the name of the EGF receptor ligand secreted by R8, 2 and 5 that leads to subsequent recruitment of cells
Spitz
What structure of the eye is derived from the retina
Retina
Which bHLH proneural gene is involved in a horizontal cell fate
Prox1
The expression of which three transcription factors characterise the eye fields
Pax6, Six3 and Rx
How are the R8 photoreceptors specified to form
Notch-delta signalling between the cells within the morphogenetic furrow acts as a lateral inhibition mechanism to space future R8 cells
Explain how the lens or optic placode is induced
As the optic vesicles grows out is touches the adjacent surface ectoderm and induces a thickening of this tissue forming the optic placode
Explain how the optic cup forms from the optic vesicle and lens placode
The lens placode invaginates with the optic vesicle to produce a double-layered cup structure referred to as the optic cup
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
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
Flies with mutant R1, 2 and 3 wont develop R7 is R8 isnt present, T or F
T – having wild type R1, 2 and 3 is not sufficient to generate an R7
Outline the process of interkinetic nuclear migration
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
What are the two structures from which the major sensory organs of the head develop from
Anterior neural tube and the adjacent cranial ectoderm
Wild type Drosophila are phototactic with a preference for UV light, what is seen in R7 mutants
They will go towards white (visible) light due to an inability to see UV light
What is the name of the structure where the axons of the R7 and R8 neurons cross over
Optic chiasm
What can be said about the cell division seen ahead of, within and behind the morphogenetic furrow
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
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
Cranial ectodermal placode
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
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
Sev and boss genes can be removed from R1-6 without causing loss of R7 specification, T or F
T
Cells of the optic stalk give rise to only one cell type, which cells are these
Astrocytes of the optic nerve
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
Reciprocal inductive interaction
What is the term given to a gene that is both sufficient and necessary to dictate the formation of particular structures
Master regulatory genes
How do the stem-like cells of the early lens differentiate
The cells of the lens elongate to form lens fibre cells
What is the significance of using notch-delta signalling in lateral inhibition
Notch delta signalling uses transmembrane ligands which limits the distance over which it can act to a single cell diameter
Homozygous mutants for Pax6 die perinatally with no eyes having developed, T or F
T
Sev is absolutely required in R8, T or F
F – sevenless is absolutely required in R7, bride of sevenless is absolutely required in R8
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
Chx10
How is the lens of the Drosophila eye formed
The cones cells of the ommatidia secrete the overlying lens
In sensory organs, the neurons develop from the neural tube. From which structure do the specialised sensory organs such as the lens develop from
Placode
Describe the cells of the mature lens
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
Describe how interkinetic nuclear migration leads to the development of a layered retina
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.
Six3, Rx and Pax6 are sufficient for eve development, T or F
T
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
Eye fields – these form the retina
Describe briefly how the cornea forms after the lens
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
What is the phenotype of Rx and Pax6 heterozygotes
Small eyes
What causes the appearance of the morphogenetic furrow
The morphogenetic furrow is caused by a shortening of the columnar epithelial cells
Rx and Pax6 homozygotes have no eyes, T or F
T
R6 and R1 are then recruited before R7 is specified last, T or F
T
Pax6 has been determined to be both necessary and sufficient to dictate eye development, what is the experimental evidence for this in Drosophila
Misexpression of human Pax6 in Drosophila leads to the development of ectopic eyes throughout the fly
Which cells of the ommatidia are the first to form
R8
How does the lens form from the optic placode
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
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
Lens fibre cells
Pax6, Rx and Six3 are extremely conserved genes. Describe the experimental evidence for this significant conservation
Insertion of the mouse Pax6 gene into the Drosophila genome and random activation leads to the development of Drosophila eyes from Pax6 positive cells
Ectopic activation of Pax6, Rx and Six3 is sufficient to induce ectopic eye development, what can be inferred about these transcription factors
They are master regulatory genes governing eye development
After the lens placode invaginates and pinches off, it forms a hollow ball of cells. What is the name given to this structure
Lens vesicle
What structure connects the optic vesicle to the diencephalon and what will the structure later become
The optic stalk – will later become the optic nerve
In which cell(s) of the ommatidia is boss expressed in
R8
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
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
A balance of which anterior-posterior patterning signals lead to the positioning of the eye fields
Wnt signalling and wnt antagonists (FGF and RA)
What type of protein is sevenless
RTK
What is meant when in development of the eye it is said that neurons are born in waves over time
Essentially, the time of when stem cell generates a neuron will determine what that particular neuron is going to be
With what you know about the cells of the mature lens, describe what cataracts are
Cataracts are a failure of the lens to make more lens fibre cells. As they are enucleate, they die within 6 weeks
What is the significance of the equator that runs through the neurocrystalline lattice structure of the Drosophila eye
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
The anterior most regions of the neural tube forms the diencephalon, T or F
T
The primary optic vesicles arise from the frontal eye fields as an evagination of the neural tube epithelium, T or F
T
