Chemotaxis Flashcards
What type of protein is mediating olfaction in the animal kingdom?
G-protein coupled olfactory receptors.
In c. elegans, what is determining the sign (attraction or repulsion) of chemotaxis?
It happens at the level of sensory neuron. By example, if you delete AWB, the worm does not know if it should avoid or be attracted to nonanone (usually avoided chemical). In the same idea, when ODR-10 is suppressed, the worm is no longer sensitive to diacetyl.
How does tracking of an odorant seems to occur in c. elegans: is it according to the bacterial model which track the change in concentration over time or by doing a left-right comparison like a snapshot of odor distribution in space?
C. elegans mostly follows the bacterial model: when there is no gradient = random walk, when there is a gradient = biased random walk. When they are attracted to a chemical, the probability to do a reversal is greater while moving down the gradient and lower while moving up the gradient. After a course change, it is more likely to be oriented up gradient. This show that there is a biased random walk. Contrarily to bacteria, they seem to remember where they were right before because they are more likely to position the right way after a reversal.
How does tracking of an odorant seems to occur in fruit fly larvae: is it according to the bacterial model which track the change in concentration over time or by doing a left-right comparison like a snapshot of odor distribution in space?
Fruit fly larvae have bilaterally symmetric chemosensory organs.
In fruit fly larvae OSN, what OR is expressed in all of them and what manipulation can we do with it afterwards?
Or83b is expressed in all OSNs. If it is not expressed, no ORs are functional. If you express Or83b with the promoter of an OR of interest (ex: Or42a), only Or42a OSN will be functional. To get chemotaxis, you only need one OR functional anyway.
What happens in fruit fly larvae if you express OSN only on one side?
The chemotaxis score is reduced: it is not doing as well to track the odorant compared to when both OSNs are functional.
How does tracking of an odorant seems to occur in mammals: is it according to the bacterial model which track the change in concentration over time or by doing a left-right comparison like a snapshot of odor distribution in space?
Mammals appear to smell in stereo: in mice, when the odor is on one side, the olfactory bulb is activated on that side. Also, when a nostril is stitched, they are less accurate in chemotaxis.
In humans, how did they prove we smell in stereo?
Made someone track an odorant by either plugging both sides of the nose to one track or not. They saw that those connected to the same track instead to have differentiated nostrils took more time to track the odorant and were less accurate.
How are odorants integrated in c. elegans?
When odorant is there, AWC neuron is off, when it is not, it gets on (takes seconds). They respond to changes in concentration of odorant. When AWC on, AIY off, AIB on (takes minutes) which leads to a turn. This regulates turning behavior.
How can c. elegans decide what is a good odor vs. not? What does it prove?
When they are in contact with pathogenic bacteria, they learn to avoid it. It is due to serotonin secreted by ADF neuron in presence of pathogenic bacteria which affects AIY neuron by activating it, leading to aversive learning. It proves that c. elegans, even if they are all the same, working in labeled lines, can show sensory learning.
