Receptor-ligand genetics: Inactivation of receptors with a modified viral protein.

Extract: The function of a gene can be genetically investigated at the DNA (gene), RNA or protein levels. Homologous recombination or gene targeting has been widely used in mice whose embryonic stem cells can be manipulated to generate mutant offspring. However, it cannot be directly applied to human genetics or primary cells. In addition, it is difficult to generate mice with mutations in multiple genes that are closely linked. Moreover, knockout mice may have cell populations that are able to compensate for the loss of gene function during embryonic development. At the RNA level, anti-sense RNA has been used with limited success. More recently, RNA interference (RNAi) has been employed to knock down gene expression in a number of organisms. Although promising, RNAi has met with various levels of success, especially if the target protein is stable, and it may influence the expression of unrelated genes through unknown mechanisms. At the protein level, one common approach to studying receptor function is through the use of blocking antibodies. However, antibodies have limitations ranging from target specificity to toxicity and in vivo efficacy. The Intrakine and Intrabody system is another method of receptor inhibition in which a cytokine or single chain antibody specific to a receptor is fused to an endoplasmic reticulum (ER) retention signal to sequester the target receptor to the ER. While the Intrakine does reduce receptor function in the target cell, it has been shown to be secreted and to stimulate receptor signaling in surrounding cells. In addition, specific targeting of proteins for degradation is being rapidly developed to investigate protein functions.