One of the most striking aspects of biology is in the diversity of cellular life. Although much of this variability has been attributed to genetic and environmental factors, recent studies have shown4 that genetically identical organisms in the same environment exhibit heterogeneity in gene expression. This phenomenon, gene expression noise, has been observed and measured across species as divergent as prokaryotes and mammalian cells.1-4
We have been keenly interested in understanding more about the origin of this heterogeneity as well as wondering what potential functional consequences it may have. We have begun addressing these questions with a suite of experiments described in the following chapters.
In Chapter 1, we examine the effects selection may have on gene expression noise in silico. We find that under fairly general conditions, directional selection for the value of a quantitative phenotypic trait can yield an increase in the noise in that trait.
In Chapter 2, we begin to look experimentally at the effects cis-regulatory mutations have on gene expression noise. Through the creation of promoter mutant libraries, we look for mutations that change noise; furthermore, by also looking at how these same mutations affect mean levels of gene expression noise, we test the independence of these two parameters. By measuring mean and noise levels of gene expression in three mutant yeast promoter libraries, we see that the two parameters are independent in some cases. More importantly, we see a wide variety of mean and noise values, suggesting that cis-regulatory mutations can control gene expression noise independently of mean.
Upon finding out that specific promoter mutations can impact gene expression noise, we were in...
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...will help uncover mechanistic insights into the observed fast bursts.
To summarize, we have looked at different potential mechanisms for generating gene expression noise, namely selection, cis-regulatory mutations, and the localization of trans-acting factors. All appear as if they could contribute to gene expression noise; most notably, the bursting of transcription factors in and out of the nucleus, in addition to leading to increased amounts of gene expression noise, also yields proportional control of a suite of genes. These results also provide a mechanism for proportional control, a phenomenon which may be important in several contexts and may even provide a rationale for some of the gene expression noise that we observe. We anticipate that further investigation of the functional consequences of noise will continue to provide insights into cellular behavior.
Jared Diamond is a professor of geography at UCLA. He has a PhD in physiology and has spent his time since then researching molecular physiology and evolutio...
3 Leicht B. G., McAllister B.F. 2014. Foundations of Biology 1411, 2nd edition. Southlake, TX: Fountainhead Press. Pp 137, 163-168, 177-180,
-Reilly Philip. Is It In Your Genes. Cold Spring Harbor Laboratory Press. 2004: 223-228. Print
Hall, Linley Erin. “Understanding Genetics DNA and RNA.” New York: The Rosen Publishing Group, Inc., 2011. Print. 01 Apr. 2014.
Some individuals have developed different traits to help them in the process of intra-sexual competition. The organisms with more distinctive traits have greater reproductive success. More genes of those traits are then ‘selected’ and are passed onto the offspring of the organisms. Throughout time variability in these traits becomes
DNA methylation is catalyzed by the enzyme: DNA methyl trasnferase (DNMTs). Methylation of DNA segments leads to the silencing of transposable elements. Hence this mechanism is repressive to transcription, by that enhancing genomic stability. However, there exist “CpG” islands that are associated with gene promoters that escape methylation hence stability.
Trafton, A. (2013, June 23). MIT News. Enhancing RNA Interference, pp. 1-2. Retrieved 12 16, 2013, from http://web.mit.edu/newsoffice/2013/enhancing-rna-interference-0623.html
"Result Filters." National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 27 May 2014. .
"Result Filters." National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 25 Apr. 2014.
... to RNA and the translation to proteins, as well as gene expression. Noble does an excellent job of presenting an opposing view to the central dogma of biology, using metaphors to attempt to make his differing views clearer to the reader. While Noble does use a lot of scientific evidence to support his opinions, his use of metaphors is overwhelming and it can easily distract the reader from the point that he is trying to make. ,Nobles’ explanations of gene expression help the reader to understand the process of evolution, giving a more or less clear view as to how redundancy in the genome can lead to variation. Noble neglects, however, to expand upon natural selection or any other ideas related to evolution. If these ideas were present, they were lost somewhere between the overwhelming use of metaphors and the overly detailed explanations of cell signaling processes.
Cain, M. L., Urry, L. A., & Reece, J. B. (2010). Campbell Biology. Benjamin Cummings.
This paper addresses a currently relevant topic of detection of associations of copy number polymorphism with traits and will be of interest to readers of Genetics Research.
Nature Publishing Group, n.d., p. 78. Web. The Web. The Web. 25 Mar. 2014. The 'Standard' of the 'Standard SparkNotes.com - a SparkNotes.com site SparkNotes - n.d. Web.
A recent field of biology, called epigenetics, is rapidly transforming previous ideas on the impact of genes. The...