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Lecture 15

Lecture 15. 3/26/13 Invertebrate phototransduction. Drosophila visual transduction. Invertebrate phototransduction. Invertebrate vision starts with absorption of photon by opsin. Drosophila eye. 800 ommatidia Single ommatidium CO corneal lens psC pseudocone PC pigment cell

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Lecture 15

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  1. Lecture 15 3/26/13 Invertebrate phototransduction

  2. Drosophila visual transduction

  3. Invertebrate phototransduction • Invertebrate vision starts with absorption of photon by opsin

  4. Drosophila eye • 800 ommatidia • Single ommatidium • CO corneal lens • psC pseudocone • PC pigment cell • CC cone cell • R photoreceptor cells

  5. Rhabdomeres are microvillar cells containing different opsins:R-opsin R1-6 like rods: sensitive+slow R7-8 like cones: high acuity, color

  6. Drosophila mutant screen • Model system • Screen for mutants which have visual defect • Find gene causing defect • Piece together genes that are important part of visual pathway

  7. Earliest mutant screens Phototaxis behavior Fly goes to the light if eyes are functioning Mutants do not

  8. Earliest mutant screens Phototaxis behavior Fly goes to the light if eyes are functioning Mutants do not

  9. Electroretinograms, ERGs • Send light pulse to eye • Wire outside of retina records voltage coming from whole eye response • Sum of all neural signals in eye

  10. Light coincident receptor potential 5 s pulse Electrical response to light flash

  11. Light coincident receptor potential Drosophila mutants 5 mV 5 s pulse Norp - no receptor potential Trp - transient receptor potential

  12. Identified > 40 genes from Drosophila mutants A few are: • norpA - phospholipase C • ninaA - rhodopin transporter • ninaC - protein kinase • ninaE - rhodopsin • Trp - cation channel

  13. Response begins with opsin bound to 11-cis retinal Rhodopsin gets turned off by being bound by arrestin Same as vert phototransduction

  14. Phototransduction pathway

  15. Phototransduction pathway TRP-TRPL likely heteromeric channels

  16. Comparison of vert and invert phototransduction

  17. Where do these pathways come from?

  18. Relationship of bilateria

  19. Vert and invert vision • Did they evolve at same time?

  20. Did ciliary and rhabdomeric pathways evolve at same time? Science 2004

  21. Both ciliaryand rhabdomericcells in worm C-opsin in brain R-opsin in eyes ae = adult eye le = larval eye Brain with cPRC – cilated photoreceptor cells So worm has both types of photoreceptors!!

  22. C-opsin and r-opsin at least to here Vertebrate camera eye Rods and cones

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