system
Given the following post, respond as if you're commenting on Reddit:
human
how do doctors tell stem cells what organ to become?

from my understanding stem cells can become any piece of tissue so even if the put a mold in the right shape how do the cells "know" to be a kidney and not a liver or just skin?
gpt
There are a number of different strategies right now:

* Small signaling molecules
* Inducing genes commonly expressed in the target cell type
* Fine-tuning surface hardness (soft surfaces promote neuronal growth, hard surfaces bone)
* Creating concoctions of growth factors and crossing fingers that THIS mix will be slightly more effective than the last one.

Cellular differentiation involves tons of genes talking back and fourth with each other, up regulating one, down regulating another. The biggest problem in the stem cell world right now is a lack of standardization. Some people have cell lines that happily differentiate into blood and liver cells, but take that same stem cell and attempt to make a neuron out of it and you're SOL. With other cell lines, the complete opposite may be true.

So how do cells know to become a kidney or a *"just"*  &#3232;\_&#3232;
 a skin cell? Cells have surface proteins that can bind to a large variety of molecules, these surface proteins start a signal cascade to some other part of the cell. So if a stem cell is surrounded by kidney cells, all making kidney proteins, in kidney salt concentrations, then it's probably going to assume it's a kidney cell.


So if we start off as a mass of stem cells why do we develop highly segregated organs instead of a massive kidney? Something about edge effects in the early embryo or something, fuck if i know.