When we were watching the DNA sequencing video a thought struck me. Very early in the video they mention how DNA consists of exons (which code for the proteins) and introns (“junk DNA”?).
I took the Intro to Stem Cells course my first year, and learned of the different type of stem cells. Obviously, The First (fertilized) Cell must be capable of differentiating into anything, and thus have chemical signals to change what sections of DNA make up introns, and which ones should be activated for exons.
A basic search of “stem cells and exons” did not bring up any research on such specificity. Then again, I’m sure it’s not easy to research. Also, the nature of stems cells means that they would have to be researched in vitro, which could of course change pathways.
I’d be curious to hear if anyone else knows more!
This is not really in response to your question but just about stem cells in general. They are such a mystery and just this week I have learnt that they promise a cure for many diseases but at the same are a reason that some diseases such as cancers and AIDS are not cured. They can harbor in their DNA the mutations or the virus causing the disease and are not responsive to drugs that mostly target the protein products of the illnesses.
I don’t have an answer to your questions as well, but I was thinking that if stem cells can be created by proteins that are coded by exons, I would expect diseased cells be easily removed to be replenished by stem cells which can basically create any type of cell. Then again, the pluripotency of stem cells can also lead to tumor genesis since these cells can form any type of cells and can have the ability to generate them uncontrollably.
Generally, differential gene expression is caused by the availability of different transcription factors as opposed to changing introns and exons. Some genes do have multiple forms because proteins can bind to the part of the DNA sequence that signals the cell to splice out part of the DNA (although this isn’t something unique to stem cells). In other words, in some cases you’re removing an intron and other times you’re tricking the cell into leaving it in.
The other really important part of what makes cells become differentiated, is that cell identity tends to be supported by positive feedback loops. So, once a cell receives a signal to becomes an endodermal cell for example, it turns on a gene that up regulates itself and represses the genes that are required to become mesoderm or ectoderm.
Hi! Not sure if I am helping to answer your question, but I’ll post what I think is relevant. if I remember correctly from genetics, an intron region and exon region is not so explicitly specified in the genomic DNA (or color-coded so neatly as it is in our diagrams!); like Alyssa, said, usually it is the presence of certain transcription factors (for ESCs, I think that usually means TFs like Oct4 and Nanog) that bind to certain regions along the DNA that helps us determine where an exon starts and ends.
For all cells, the biological environment (i.e., presence of certain regulatory proteins) is really key – this can be observed by placing four transcription factors (Oct4, Nanog, Klf4, c-Myc) in differentiated fibroblast cells in vitro and reprogramming them back to a pluripotent state. These proteins upregulate genes associated with pluripotency and repress genes associated with differentiation, as mentioned before.
Thank you for all the great responses!