In: Biology
It is known that a human protein is expressed only in the brain. There is an identical but smaller protein that is expressed only in the liver. What experiments would you use to determine the origin of this differential expression?
The protein is expressed only in the brain. However, an identical but a smaller protein is expressed only in the liver. Therefore, the protein is showing differential expression across tissues.
To check for the origin of this differential expression, we can perform cloning experiments.
The expression of a gene is controlled by the promoters and enhancers. Hence, we are basically interested in determining the region upstream to the gene that is involved in the differential expression. For this, we can clone the upstream segment of the gene upstream to a GFP in a plasmid. This plasmid can then be cloned in both brain and liver cells. Whenever the GFP is expressed in either of these cells, the corresponding upstream sequence is responsible for driving the expression in the respective cells.
Moreover, the liver protein is smaller. Hence, clearly the protein is being produced here with an alternative splice isoform. To determine, which exon(s) is/are removed in the liver protein, we can isolate the RNA and convert it to cDNA. The cDNA can then be PCR amplified and sequenced. The two sequences can then be compared to determine the exon(s) that is/are lost in the liver.