gene expression

Examples of gene expression in the following topics:

• Prokaryotic versus Eukaryotic Gene Expression

  • Prokaryotes regulate gene expression by controlling the amount of transcription, whereas eukaryotic control is much more complex.
  • To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell.
  • Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
  • The regulation of gene expression can occur at all stages of the process .
  • Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm.

• The Process and Purpose of Gene Expression Regulation

  • At any given time, only a subset of all of the genes encoded by our DNA are expressed and translated into proteins.
  • The expression of specific genes is a highly-regulated process with many levels and stages of control.
  • In this section, you will learn about the various methods of gene regulation and the mechanisms used to control gene expression, such as: epigenetic, transcriptional, post-transcriptional, translational, and post-translational controls in eukaryotic gene expression, and transcriptional control in prokaryotic gene expression.
  • The genetic content of each somatic cell in an organism is the same, but not all genes are expressed in every cell.
  • The control of which genes are expressed dictates whether a cell is (a) an eye cell or (b) a liver cell.

• Cell Signaling and Gene Expression

  • Gene expression, vital for cells to function properly, is the process of turning on a gene to produce RNA and protein.
  • The process of turning on a gene to produce RNA and protein is called gene expression.
  • The regulation of gene expression conserves energy and space.
  • The control of gene expression is extremely complex.
  • The regulation of gene expression can occur at all stages of the process.

• Mammalian Gene Expression in Bacteria

  • Bacterial genetics can be manipulated to allow for mammalian gene expression systems established in bacteria.
  • Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product.
  • In a genetically engineered system, this entire process of gene expression may be induced depending on the plasmid used.
  • In the broadest sense, mammalian gene expression includes every living cell but the term is more normally used to refer to expression as a laboratory tool.
  • E. coli is one of the most popular hosts for artificial gene expression.

• Altered Gene Expression in Cancer

  • Cancer, a disease of altered gene expression, is the result of gene mutations or dramatic changes in gene regulation.
  • Cancer can be described as a disease of altered gene expression.
  • There are many proteins that are turned on or off (gene activation or gene silencing) that dramatically alter the overall activity of the cell.
  • A gene that is not normally expressed in that cell can be switched on and expressed at high levels.
  • This can be the result of gene mutation or changes in gene regulation (epigenetic, transcription, post-transcription, translation, or post-translation).

• Tracking Cells with Light

  • This can be achieved by using tools to monitor gene expression to track when proteins are made and where they go in the cell.
  • It is important to use a reporter gene that is not natively expressed in the cell or organism under study, since the expression of the reporter is being used as a marker for successful uptake of the gene of interest.
  • In cells where the gene is expressed, and the tagged proteins are produced, GFP or luciferase are produced at the same time.
  • GFP as biomarker is also useful in monitoring gene expression and protein localisation in bacterial cells.
  • Reporter gene used as an indication of the regulatory sequence expression in the cell.

• Gene Inversion

  • Gene Inversion utilizes recombinases to invert DNA sequences, resulting in an ON to OFF switch in the gene located within this switch.
  • There is also a change in orientation of the DNA that will affect gene expression or the structure of the gene product.
  • Many bacterial species can utilize inversion to change the expression of certain genes for the benefit of the bacterium during infection .
  • The inversion event can be simple by involving the toggle in expression of one gene, like E. coli pilin expression; or more complicated by involving multiple genes in the expression of multiple types of flagellin by S. typhimurium.
  • The FimE recombinase has the capability to only invert the element and turn expression from on to off, while FimB can mediate the inversion in both directions.

• Epistasis

  • Epistasis occurs when one gene masks or interferes with the expression of another.
  • Genes may also oppose each other with one gene modifying the expression of another.
  • In epistasis, the interaction between genes is antagonistic: one gene masks or interferes with the expression of another.
  • Epistasis can also occur when a dominant allele masks expression at a separate gene.
  • Homozygous recessive expression of the W gene (ww) coupled with homozygous dominant or heterozygous expression of the Y gene (YY or Yy) generates yellow fruit, while the wwyy genotype produces green fruit.

• Epigenetic Alterations in Cancer

  • Silencing genes through epigenetic mechanisms is very common in cancer cells and include modifications to histone proteins and DNA that are associated with silenced genes.
  • Histone proteins that surround that region lack the acetylation modification (the addition of an acetyl group) that is present when the genes are expressed in normal cells.
  • When these modifications occur, the gene present in that chromosomal region is silenced.
  • In cancer cells, silencing genes through epigenetic mechanisms is a common occurrence.
  • Describe the role played by epigenetic alterations to gene expression in the development of cancer

• Reporter Fusions

  • Certain genes are chosen as reporters because the characteristics they confer on organisms expressing them are easily identified and measured, or because they are selectable markers.
  • Reporter genes are often used as an indication of whether a certain gene has been taken up by or expressed in the cell or organism population.
  • It is important to use a reporter gene that is not natively expressed in the cell or organism under study, since the expression of the reporter is being used as a marker for successful uptake of the gene of interest.
  • This enzyme causes bacteria expressing the gene to appear blue when grown on a medium that contains the substrate analog X-gal.
  • Reporter genes can also be used to assay for the expression of the gene of interest, which may produce a protein that has little obvious or immediate effect on the cell culture or organism.