How, and where, does gene expression work?

Richard Alex won (1/2 of) the 2004 Nobel Prize in Medicine / Physiology for his (joint) work on the olfactory system. His work is crazy and wonderful; you can listen to a talk on the topic, or read a transcript, from some recent conference at Columbia University.Here's an article about cloning a mouse based on the DNA of a 'mature' (i.e. non-dividing / replicating) cell, one of the olfactory neurons.This article brings up some issues about gene expression that I'd like to know more about. It's been puzzling me, and continues to puzzle me.

1. I know that gene expression can be based on many 'factors'.Here's two that I know.
   
   • the presence of molecules in the cell that directly trigger gene expression (forgot the technical term)
   • the absence of molecules in the cell that directly inhibit gene expression (forgot the term)
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2. The article says the researchers thought the olfactory sensory neuron 'mature' cells might:
   
   • choose the single gene (out of a pool of more than 1000) which they express (and thus sense some aspect of smell) due to some re-arrangement of the cell's DNA.
   • fail to replicate because of this suggested rearrangement
   
   
   The researchers chose olfactory neurons as the source of genetic material because previous research had suggested that these cells might undergo gene rearrangements during development. Whatever the underlying process involved in generating their spectacular diversity, olfactory neurons are distinguished by their ability to randomly express any one of some 1,500 diverse odor receptor genes. Such genes give rise to the protein receptors on the surface of the neurons that detect specific chemical odorants.
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3. The researchers WERE able to clone using this DNA, suggesting either:
   
   • The cell's DNA was not re-arranged OR
   • The cell's DNA was re-arranged, BUT it was reversible.
   
   
   According to Axel, the cloning achievement eliminates one potential mechanism and narrows the possible ways in which a cell chooses one of thousands of receptor genes. The findings also demonstrate that the developmental changes are reversible.
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4. Finally, Axel suggests at the end of the article that this technique is applicable to discovering these facts about other cells.
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   Axel said that the cloning technique should be broadly applicable. gFrom a mechanistic point of view, it's very important to be able to investigate whether irreversible changes in the DNA accompany development, differentiation and maturation,h he said. gThis approach, although technologically demanding, affords an opportunity to detect those changes that are irreversible in virtually all cells.

OK, FINALLY!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.Please, help!!BenP.S. This stuff is so cool!edited: trying to change non-descript titleThis message has been edited by bencip19, 12-12-2004 01:31 AMADMIN: can you change the title of the thread to 'How, and where, does gene expression work?' and to remove the subttile? Heck, remove this message too Thanks.This message has been edited by bencip19, 12-12-2004 01:32 AM

(sheepishly) .. any takers?(pacing slowly while looking at my feet, and my hands behind my back)Ben

WK,Thanks for the post. I read it through yesterday, and I'll go through more thoroughly this week.My goal is to understand these issues so that, when talking about genetics and especially gene expression and it's role in brain development, I have a better understanding. Kandel gave a talk about long-term memory vs. short-term memory, and labeled it "genetic vs. non-genetic" memory. But of course (given the audience) he glossed over the actual details.So, just to say thanks and explain the relevance of this for me. Thanks!Ben