7TM receptors: the splicing on the cake

Within a given family of seven transmembrane domain (7TM) receptors, functional diversity is most often afforded by the existence of multiple receptor subtypes, each encoded by a distinct gene. However, it is now clear that the existence of introns in genes encoding some members of a receptor family provides scope for additional diversity by virtue of splicing events that result in the formation of different receptor mRNAs and consequently distinct receptor isoforms. A large number of 7TM receptor splice variants have now been shown to exist. In this article, the current data on alternatively spliced variants for hormone and neurotransmitter 7TMs are reviewed, their potential physiological importance considered and some of the issues pertaining to the classification and nomenclature of receptor isoforms produced in this way are addressed.