Drosophila Eye Development Flashcards
What are imaginal discs?
Areas which develop into the mouth, eye etc
When are imaginal discs set side?
In early embryogenesis
What is the haltere?
A balance organ
How many cells gather to form an imaginal disc?
Around 30
How big do structures from imaginal discs grow?
To about 50,000 cells
What is the phenotype of a Pax 6 mutant?
They have no eyes
What is eyeless?
A homeobox transcription factor homologous to vertebrate PAX6
Eyeless PAX6 is both … and … to make an eye
necessary
sufficient
PAX6 misexpressed in a fly induces what?
An ectopic eye
How many flies do drosophila have?
5 - 2 large and 3 small
What are the flies small eyes called?
Ocelli
What are ocelli used for?
Sense the flies orientation ie where they are in the sky
Each large eye consists of how many ommatidia?
800
What are ommatidia?
each of the optical units that make up the compound eye of an insect.
Why are the ommatidia hexagonal?
Makes them efficient in their packaging
Each ommatidia is associated with what?
A bristle involved in the cleaning process
Why are the fly eyes curved?
To give them a wide plane of view
Each ommatidia consists of:
8 photoreceptors 4 cone cells 2 primary pigment cells 6 secondary pigment cells 3 tertiary pigment cells
Why do fly eyes contain red granules around the lens?
They stop light from other places being scattered so light is focused in a straight line on the ommatidia
Why does a white mutant have worse vision than a wildtype fly?
The white mutant has no red granules so the light scatters and confuses things
What are rhabdomeres?
Light sensitive structures
They trigger neuronal input
Made of microvilli packed with rhodopsin
How many rhabdomeres are there?
7
What is the role of the equator across the eye?
It senses the horizon
Where do R1 to R6 axons project into?
The lamina
Where do R7 and R8 photoreceptors project to?
The medulla
Why can a single object be seen by many rhabdomeres?
It increases resolution
What do flies respond to?
Movement
When does most growth of the eye field occur?
The third instar
Photoreceptors are preceded by what?
The morphogenetic furrow
Describe the morphogenetic furrow
Rich in actin
Moves across the disc from the posterior to the anteror
Has very few photoreceptors
Which is the first cell to be recruited in the ommatidia?
R8 - they are born with in the morphogenetic furrow
How are R8 cells recruited?
Using a process of lateral inhibition through Notch singalling - this inhibits other cells to become R8 cells
Describe the order which Rhabdomeres are recruited
1) R8, R2 and R5 secrete EGF pathway ligand Spitz
2) R3, R4 , then R1 and R6 recruited
3) R7 is the last
4) Then cone cells are recruited after
Mutants lacking R7 can not see what?
UV light
This means they go towards white light rather than UV light
Where are R8 cells born?
The morphogenic burrow
Mutations in which genes causes the loss of R7?
Boss and sevenless
What does the gene sevenless do?
Trans membrane receptor kinase
Activator of the Ras/Raf/Erk pathway
Expressed in R8,1,6,4,3,7 and con cells
What does Boss do?
A membrane tethered ligand specific to sev
Expressed eclusively in R8
