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For example, in a systems biology analysis, what is a "downstream target" and why are these significant in pathway analyses?

I have looked for answers on Google, DuckDuckGo, Wikipedia, etc. but I have not seen a clear definition that explains what it is.

My guess is:

For downstream targets, these are targets (e.g., a protein) that are affected by upstream targets (e.g., another protein) in some kind of pathway (e.g., some pathway related to cancer). It is called a downstream target because it is used to signify where it is in the pathway (located downwards in the pathway) and that it's being affected by something, as opposed to them affecting something (which would make it upstream target)?

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    – bob1
    Oct 10 at 7:43
  • $\begingroup$ Is there a particular instance or area of research you're applying this to? You use the cancer tag and molecular biology tag, is it some related field? $\endgroup$ Oct 10 at 12:50
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    $\begingroup$ I found this via google ("systems biology upstream downstream"), i believe it is the answer to your question: en.wikipedia.org/wiki/Upstream_and_downstream_(transduction). It is not a great page as these things go, but it gets the gist that downstream is "stuff affected by the entity in question". $\endgroup$ Oct 10 at 19:13
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    – tyersome
    Oct 10 at 23:29
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    – Ollie
    Oct 11 at 14:43
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It's mostly just a flowery extra word in there when you also have the word "target".

If you imagine a signalling pathway as a river/stream, then you have some parts of the pathway that are toward the beginning of the river, and you have some that are towards the end of the river, but up/downstream really all depends on where on the river your reference point is. Targets are pretty much always going to be downstream by definition, though, unless you're talking about a feedback loop where two parts of a pathway are connected bidirectionally.

I don't think it makes much sense to have a "definition" for "downstream target" any more than you have a definition for most pairs of adjective-noun; there's no special extra meaning here besides the stream metaphor.

As far as importantance, well, nothing in biology really does anything by itself: everything acts on something else. For a protein or other molecule in a signalling pathway, you can understand the significance of that entity in the pathway only by what other entities it affects.

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  • $\begingroup$ @luuuna If someone refers to an upstream target, probably something else is doing the targeting. $\endgroup$
    – Bryan Krause
    Oct 11 at 3:44
  • $\begingroup$ @luuuna I'm going to let you just think on this. I'd highly recommend working on being more wholistic in your thinking. Knowing these answers really isn't going to teach you any biology. $\endgroup$
    – Bryan Krause
    Oct 11 at 3:46
  • $\begingroup$ @luuuna I mean to think less about this narrow question you have and more about everything else going on. Understand what's actually happening and what's important from that, not what these particular words mean just because someone else indicated that's important. $\endgroup$
    – Bryan Krause
    Oct 11 at 5:12

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