[FOREIGN]. Linda Buck and Richard Axel, [FOREIGN] in 1991 they published a paper. That paper actually a cloned the OR gene, odor receptor gene from the rat, from the [FOREIGN]. And they found actually, it's quite surprising. In the rat, there are about 1,000 OR genes, more than 1,000 OR genes in the rat. In the mouse is about 1,400. And then, there are some pseudogenes but then the functional gene is over 1,000. In rat there is actually much, is more than the mouse genes. So the total gene in the genome, roughly how many? It's about 20,000, right. So if we have more than 1,000 then almost actually about 45% of the gene in the genome devoted for the olfaction. This is surprising, right? Olfaction [FOREIGN]. So it's important the olfaction, obviously. For a lot was animals, as we said, they detect the food of the worst enemies for their survival or maybe find the mating partner, they need olfactory cues. They cloned this gene and then as they really make a huge impact in the field, then people start to okay, so this system actually is different from the visual system. It's also different from their hypothesis, each receptor detect one chemical because right now you only have 1000 for example in the mouse, the functional gene. And then the mouse can detect tens of thousands of chemicals. So then you already have a flavor how the system should work. [FOREIGN] Use one thousand gene to detect tens of thousands of chemicals. [FOREIGN] Okay. >> [INAUDIBLE] >> [FOREIGN]. That's good. That's a very good insight. [FOREIGN]. Indeed, laser a lot of studies confirmed that hypothesis. Really good. So actually in 2004, they gotten the Nobel Prize for this work. So they cloned this gene and then they wanted to know, okay so we have around 5 million olfactory sensory neuron in the nose. [FOREIGN] Sensory neuron [FOREIGN]. So you got neuron, one neuron expressed many different types of olfactory receptors or one neuron just express one type of all the receptors. They don't know. So they did experiments actually here, then they use the use different probes. [FOREIGN]. There's 1000 type of receptors. So each one type of receptor detect is about 0.1% [FOREIGN] receptor [FOREIGN]. Then the did other experiments to confirm indeed each receptor neuron or sensory neuron only express one type of odor receptor. [FOREIGN]. 5 million and 1,000. How many? 5,000, right. [FOREIGN]. [FOREIGN]. It's quite a challenge actually for, if you want to study those sensory neurons. [FOREIGN]. If you want to find a specific type of receptor neuron for the recording is quite challenging. [FOREIGN] olfaction [FOREIGN]. So if you want to study this neuron, olfactory sensory neuron, do the then you need to identify them, right? [FOREIGN] Like a receptor. [FOREIGN] Like a stimulation, just put on a chemical. [FOREIGN] Chemical [FOREIGN]. So for this kind of study actually is quite difficult even if you have 5,000 neurons, express one type of receptor. You can express GFP under that promoter of this receptor. But still, you can only find or one or few of these kinds of receptor neurons, during the recording if we isolate them. This is kind of a difficult study. So in any case, the principle is one sensory neuron only express one type of odor receptor. Let's take a look. This is, actually is receptor gene is the main protein here. Is typical. And then this one is quite cross one southern type of odor receptor, this actually maybe features for the. And this black one, actually quite different across different receptors. So what do you think? This different than. So they are different because the key features, the common features maybe for signalling is binding to the g protein, right? Those should be similar, but if they are different then in most case may be related to the recognition of different chemicals. For example the. So here then actually is the [FOREIGN] odor receptors only enriched in the olfactory [FOREIGN], this is some information. And take a look here, this one. In human, we have in total it's about 800 odorant gene. But they are, about 400 odorant gene are pseudo-gene. Function, almost half. No function. It is quite surprising right? And you can take a look actually here. Like a rat, [FOREIGN] function odor. In the mouse, [FOREIGN] pseudogene, [FOREIGN] function odor. >> [INAUDIBLE] >> [INAUDIBLE] >> About what? [FOREIGN]. [FOREIGN] Why in the human actually we have much fewer odor receptors compared with the lower order animals. >> [INAUDIBLE] >> Okay, yeah this actually evolution or the kind of selective pressure. So then has a lot of those pseudogene happened, actually selected out. That's good. So, indeed, people believe within the field is, why in the human the olfactory system are not comparable to the mouse, the dogs. That's because human actually rely on the color vision. [FOREIGN]. The color vision is so powerful for human to recognize the food, in the jungle, not human, for monkey. Human we are fine right now, right. We don't rely on olfaction. You have a coat, you are fine. [FOREIGN] Not such a critical thing. But as I said, for human, the olfactory system is mainly for those long term memory and control your emotion and it's the other things. We know one sensory neuron only expresses one type of receptors. They select one type of receptor from 1000 types of receptors. Only express one. This is really quite interesting topic. How the cell can do this thing. Make the decision, select only particular one. Indeed it is like really a fundamental question in the field. A lot of really good labs actively study this topic. Yeah it does include a lot famous labs. Even Richard Axel. Also interested is one like and also some other labs. So to answer, I guess a lot of important studies suggest that system works is because there is some mechanism within the cell. When the cell expresses one type of receptor, and then that receptor can inhibit the other receptor expression, there's a kind of dis-controlling mechanism. This is quite interesting, right? But most important is, how did that cell convert in the first place to express the OR gene? That's the key. [FOREIGN] Control. >> [FOREIGN] >> Yeah. >> [FOREIGN] >> Okay. >> [FOREIGN] >> Yeah >> [FOREIGN] >> [FOREIGN] >> [FOREIGN] >> Okay, [FOREIGN].
