User:Mkingston10/sandbox

Ryan Murphy and Mackenzie Kingston are collaborating on two separate, unrelated articles.

Our topics are Ectopic Expression (previously a stub) and Splice Junction (new article)

The words used from the ectopic expression stub are italisized

Ectopic expression
Ectopic expression is the expression of a gene in a tissue in which is it not normally expressed. The ability to artifically produce ectopic expression is a powerful way of determining a gene's function in a variety of model organisms. Ectopic expression of a gene can be achieved by introducing a transgene with a modified tissue specific promoter into a target organism. More apparent is the use of ectopic expression to generate abnormal dominant gene function. Less apparent is to use ectopic expression of transcription factors that antagonize endogenous gene products, to generate endogenous gene loss of function. Normally with age cells will degenerate and as a consequence many wild-type proteins will lose their function. Compensation for wild-type protein loss of function by ectopic expression of genes that code for these proteins is an approach with therapeutic potential.

Drosophila GAL4-UAS system
Ectopic expression of a gene can be done by using the Gal4-UAS system. The GAL4-UAS system was created by geneticists for targeted gene expression to investigate gene function in Drosophila. Initially in the GAL4-UAS system, GAL4 and UAS-target genes are found in two different transgenic Drosophila lines. The GAL4 transgenic line is crossed to the UAS-target gene transgenic line and as a result the target gene is expressed in the offspring. A tissue specific promoter is able to control expression of GAL4—a yeast transcription activator—which activates UAS target gene transcription. A well-known application using the GAL4-UAS system for ectopic expression in Drosophila is the Antennapedia gene. Antennapedia is normally only found in the second thoratic segment in Drosophila larvae. By ectopic expression in the anterior tissue of Drosophila larvae a second pair of legs grows in place of antennae, implying Antennapedia’s role in leg development. The GAL4-UAS system has also been used to discover the function of many other genes through ectopic expression and the formation of abnormal Drosophila body plans including eyes being formed on wings, antennae and legs.

Induced pluripotent stem cells
Ectopic expression is capable of generating induced pluripotent stem cells (iPSCs) for use in disease modelling and treatment. Genes screened specifically in embryonic stem cells (ESCs), identified multiple transcription factors responsible for the induction of pluripotent stem cells. iPSCs unlimited self-renewal and differentiation abilities show potential for regenerative medicine, cell-based therapy, disease modelling and drug discovery. Ectopic expression makes possible the generation of iPSCs which lack the ethical and moral concerns surrounding the use of embryonic tissues.

Senescence
Inducing cellular senescence utilizing ectopic expression is a potential anticancer mechanism. Cellular senescence can be divided into replicative cellular senescence and premature senescence where the former is due to telomere length and the latter to cellular stress. Some oncogenes (e.g. RasG12V, B-RafV600E and c-MYC) can be ectopically expressed to induce cell senescence by activating a DNA damage response independent of telomere length. This form of stress-induced senescence is called "oncogene-induced senescence" is rapidly activated when oncogene stress is present resulting in death in vitro. Oncogene induced senescence may serve an anti-tumorigenesis mechanisms in vivo through the ectopic expression of certain oncogenes.

Splice junction
Splice Junction is a two nucleotide long sequence found in introns that define the boundaries of exons. Splice junctions are the most important feature for exon recognition, at which the spliceosome assembles.The GT-AG rule describes the 5' and 3' splice junction sequences at the first and last two nucleotides of nuclear introns. Mutations at splice junction sites cause abnormalities in splicing, can be very deleterious to the organism. In humans, splice junction mutations make up approximately 15% of all point mutations that result in genetic disease.