Mosaic Analysis Reading: 152-155; 731-732 & lecture notes Problem set 7.

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Presentation transcript:

Mosaic Analysis Reading: ; & lecture notes Problem set 7

The Drosophila eye Composed of several hundred repeating units known as ommatidia Each ommatidium has 8 photorecetor cells, 4 cone cells, pigment cells and a sensory bristle.

Drosophila eye development

Visible UV When given a choice of light preference

Visible UV Drosophila prefers UV

Visible UV Screens for UV blind flies.

UV blind flies Defective in rhodopsin that detects UV Missing R7 (R7 photoreceptor cell that contains UV senesitive rhodopsin)

In both sev and boss mutants, R7 is missing because it is transformed into a cone cell wild-type sev - or boss - No R7

If Boss is a ligand for the RTK Sevenless, then Boss’s function should be required in a cell other than R7 and Sev should be required in R7. Ras

In 1936 Curt Stern observed twin spots y + sn / y sn +

…and explained the patches by mitotic recombination

But first a note on how mosaics were used to show how the fly eye develops. R1 R2 R3 R4 R5 R6 R7 R8 Invariant lineage? Like C. elegans R1 R2 R3 R4 R5 R6 R7 R8 R3 R1 R4 R7 R6 R8 R4 R5 No lineage restrictions? And all other combinations!

Mutant clone Analyze ommatidia at the periphery of mutant clone. These will be mosaic, containing both wild-type (red) and mutant (white) cells.

Irradiate white/+ animals and study mosaic eyes. R1 R2 R3 R4 R5 R6 R7 R8 If invariant lineage, then lineage relationships will be maintained in white clones.

R1 R2 R3 R4 R5 R6 R7 R8 R3 R1 R4 R7 R6 R8 R4 R5 If not invariant then there will be no lineage relationships among cells in clone. This is what happens! Any cell can adopt any fate. Cells are specified entirely by cell interactions. Etc…

Boss expression is restricted to R8, but Sev is expressed in R1, R3, R4, R6, R7, the precursors to the cone cells and mystery cells. 1. Does Boss function in R8 as predicted by its expression pattern? 2. Does Sev function in R7, or is signaling to the R7 cell via Sev more complex?

white can be used as cell autonomous marker to monitor the loss of sev.

sev is required in the R7 cell; it functions cell automomously

w - /w - ; boss - /boss + P[white+] Can use P element mediated transposition to insert white on other chromosomes. w-w- w-w- boss- P[w + ] boss +

boss is required in the R8 cell; it functions cell nonautomomously

Ras