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My question is, how much do we know about gene expression? What are the ways that gene expression can happen? And what gene expression goes on that we really don't know how it's happening? For example, how does gene expression works such that a cell 'decides' it's going to express this ONE gene out of a pool of more than 1000, even though it is identical to all the other olfactory sensory cells otherwise.
As the title of my post says, there are as many mechanisms for gene expression as there are ways to skin a cat. Just a wild guess, a hypothesis if you will, the olfactory expression may be a "first come, first serve" type of expression. The first gene to be fully expressed may shut down the expression of the other olfactory genes. This would require receptor turnover (ie removal and replacement) because there would be an initial, but limited expression of a number of receptors early on. I could prattle on about this subtopic, so I'll move on.
Gene expression is a very diverse subject. Most gene expression involves something binding to the DNA which initiates trascription or the removal of something from the DNA which initiates transcription. Then there are also invertases. I have only read a couple papers on this, but it is quite interesting. In some bacteria (typhirium IIRC) there is an enzyme that snips the DNA and inverts the whole thing upside down. This actually turns the gene "on" and allows transcription of a whole host of genes. The invertases are thought to have been derived from viral enzymes that perform similar tasks during insertion and infection.
It is very difficult to describe gene expression in over-arching themes because each gene is almost a new case in itself. Also, there are often cascades, or the upregulation of a whole suite of genes by a single regulator. Gene expression is one of those things that "If you can imagine it, it probably happens" sort of phenomena.
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