Mosaic Analysis Reading 152 155 731 732 lecture notes Problem set 7 The Drosophila eye QuickTime and a decompressor are needed to see this picture 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 When given a choice of light preference Visible UV QuickTime and a decompressor are needed to see this picture QuickTime and a decompressor are needed to see this picture QuickTime and a decompressor are needed to see this picture QuickTime and a decompressor are needed to see this picture QuickTime and a decompressor are needed to see QuickTime this picture and a decompressor are needed to see this picture Drosophila prefers UV Visible UV QuickTime andQuickTime a and a QuickTime and a decompressor decompressor decompressor are needed to see arethis needed picture to see this picture are needed to see this picture and aQuickTime and a QuickTime and a QuickTime decompressor decompressor decompressor are needed thisneeded picture to see this picture are needed to see this picture to see are Screens for UV blind flies Visible UV QuickTime and a QuickTime and a QuickTime and a decompressor decompressor decompressor are needed to see this arepicture needed to see this are picture needed to see this picture QuickTime and a decompressor are needed to see this picture QuickTime and aQuickTime and a QuickTime and a decompressor decompressor decompressor are needed to see are thisneeded picture to see this picture are needed to see this picture 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 bossNo 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 Invariant lineage Like C elegans No lineage restrictions R1 R2 R3 R4 R5 R6 R7 R8 R1 R2 R3 R4 R5 R6 R7 R8 And all other combinations R3 R1 R4 R7 R6 R8 R4 R5 Analyze ommatidia at the periphery of mutant clone These will be mosaic containing both wild type red and mutant white cells Mutant clone Irradiate white animals and study mosaic eyes If invariant lineage then lineage relationships will be maintained in white clones R1 R2 R3 R4 R5 R6 R7 R8 If not invariant then there will be no lineage relationships among cells in clone R1 R2 R3 R4 R5 R6 R7 R8 R3 R1 R4 R7 R6 R8 R4 R5 Etc This is what happens Any cell can adopt any fate Cells are specified entirely by cell interactions 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 Can use P element mediated transposition to insert white on other chromosomes w w boss boss P white w boss w P w boss boss is required in the R8 cell it functions cell nonautomomously Ras
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