GENETIC MANIPULATIONS OF CHOLINERGIC COMMUNICATION REVEAL TRANS-ACTING CONTROL MECHANISMS OVER ACETYLCHOLINE-RECEPTORS

Several approaches have been developed for genetic modulations of rece ptor expression. These initiated with gene cloning and heterologous ex pression in microinjected Xenopus oocytes, and proceeded through trans genic expression and genomic disruption of receptor genes in mice. In addition, antisense treatments have reduced receptor levels in a trans ient; reversible manner. Integration of foreign DNA with host genomic sequences yields both cis- and trans-acting responses. These may depen d on the DNA integration site, host cells condition and, most importan tly, the affected signal transduction circuit. For example, acetylchol inesterase (AChE) overexpression in microinjected Xenopus tadpoles has been shown to upregulate alpha-bungarotoxin binding levels, indicatin g trans-acting control conferring overproduction of muscle nicotinic a cetylcholine receptors. In transgenic mice expressing human AChE, the hypothermic response to oxotremorine was suppressed, reflecting modifi ed levels of brain muscarinic receptors. To dissociate the feedback pr ocesses occurring in transfected cells from responses related to DNA i ntegration, we examined the endogenous expression of the alpha(7) neur onal nicotinic acetylcholine receptor in PC12 cells transfected with D NA vectors carrying alternative splicing variants of human AChE mRNA. Our findings demonstrate suppression of alpha(7) receptor levels assoc iated with the accumulation of foreign DNA in the transfected cells. A cetylcholine receptor levels thus depend on multiple elements, each of which should be considered when genetic interventions are employed.