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My textbook tells me that it’s specific transcription factors that allow for a different set of genes to be expressed in different cells (differential gene expression). My book gives the example of liver and lens cells—liver cells contain the specific transcription factors (STFs) to activate the enhancer for the albumin gene, while lens cells contain the STFs to activate the enhancer for the crystallin gene. Liver cells do not have the STFs to activate the crystallin gene, and lens cells cannot activate the album gene.

However, my book also tells me that there is a basal level of transcription that arises from the binding of general transcription factors. Enhancers only increase the rate of transcription on top of that basal rate. Does this mean that in differentiated cells, all genes are indeed transcribed? I.e. a lens cell does transcribe the gene for albumin and the liver cell does transcribe the gene for crystallin?

(The wording of my book dissuades me: "Liver cell: The albumin gene is expressed, and the crystallin gene is not. Lens cell: The crystallin gene is expressed, and the albumin gene is not.”)

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  • $\begingroup$ Theoretically, yes. They are all transcribed, but in trace amounts. And because hepatocytes do not need crystallin, it might get degenerated by proteases or processed into another protein by ER and golgi bodies. $\endgroup$ – another 'Homo sapien' Mar 13 '16 at 2:50
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    $\begingroup$ No, there are genes that are completely turned off. As in, our current technology cannot amplify any transcripts to detect in sequencing. If you do full high sensitivity RNA-seq in different cell types, you will find some transcripts for which there are zero reads (above noise) in each type, and they will be a different overall set based on cell type. In addition, some genes are silenced after development. This silencing is usually through histone modifications that completely abrogate the ability for transcription factors to even bind to the DNA. $\endgroup$ – akaDrHouse Mar 13 '16 at 21:41
  • $\begingroup$ This answer and the paper referenced therein may answer your question, if you still care after all these years. $\endgroup$ – canadianer Apr 19 '18 at 8:31
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No Not all genes are transcribed, repressor proteins and nuclear receptors can bind the DNA preventing transcription of particular genes. Even things like histone regulation can prevent transcription. There may even be epigenetic regulation of transcription.

Source 1

Source 2

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I think genes are transcribed but either mRNA is not transcloated (moved) into the cytoplasm or they are not translated (maybe degraded).I think if you do RNA screening you will get same positive results in both liver and lens cells (as transcription occurred and if your procedure is not having any error) but if you do a western blot, the result will change as now we are seeing the things at the protein level. So even though all of our cells have same gene composition depending upon the tissue and organ they have differential RNA selection so that they will not waste resources in making unwanted proteins.

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  • $\begingroup$ A source would be important, especially for an "I think" answer. $\endgroup$ – John Apr 14 at 17:35
  • $\begingroup$ Sorry, yes I should have given the proof. You could read it in Developmental Biology Gilberts 6th edition, here is the link of the book from NCBI ncbi.nlm.nih.gov/books/NBK10112 $\endgroup$ – Sarannya E Apr 16 at 8:53
  • $\begingroup$ You should add that is not the answer, I can't change my vote unless you edit it anyway. $\endgroup$ – John Apr 16 at 12:06

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