Wednesday, June 27, 2012

ISOT 2012, dag fem

(For previous entries, see days one, two, three, and four.)

Kristin Scott:

The Scott lab focuses on taste receptors and circuits in drosophila, and today she presented two new stories.

On the receptor side, the Scott lab had identified the receptor for 3/4 of the cells in the fly taste ganglion, the SOG. Today she presented one channel for the last cell, ppk23. Another ppk, ppk25 was previously identified as a water/stretch receptor for flies. Ppk23 expression is sexually dimorphic: male flies' ppk25 cells project across the midline while females' do not; furthermore ppk23 is coexpressed with fruitless. They knocked ppk23 out, and found that male flies could no longer distinguish between males and females, and started courting male flies. Since ppk23 is in "taste" cells, they guessed it might be detecting sexually dimorphic surface hydrocarbons, and presented these hydrocarbons to the fly. Using calcium imaging they found two cells in the SOG that responded: one to male hydrocarbons, and the other to female. There are many other ppks expressed in those cells, so it's unclear whether ppk23 is the actual sensor or simply involved in signal transduction.

The second story concerned modulation of feeding behaviour. In a paper earlier this year, the found that dopamine activity  increases with hunger, and that dopamine activation can drive increased feeding behavior. Here they looked for neurons that drive satiety.  They generated GAL4 lines, and then measured how much sucrose the flies would accept. One line, 98, were "insatiable," and drank well beyond WT flies. In fact, they eagerly drank bitter fluid, or oil as well. The 98 line labelled ~30 cells in the SOG, so now they are trying to use mosaics to pin down the exact cells.

Robert Barretto:

Rob expanded on what Zuker previewed the first day: 2p endoscopy in the taste ganglion. He described seven populations: five single tastes, and two pairs, sweet/umami ans bitter/sour. Notably, umami was represented the least,  by far, with 30/1200 cells. In comparison, during the questions, he mentioned that 15-20 cells represented another pair, sour/salty (I think).
After his talk, a few people approached him with further questions. Since he did not publicly say them, I will refrain from repeating them. Suffice it to say that consideration of stimulus concentration, and crosstalk between receptors (e.g. artificial sweeteners and bitter) is essential to interpreting the results.
And with that the conference is over.

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