NEUREXINS - 3 GENES AND 1001 PRODUCTS

The human brain has approximately 10(12) neurons, three orders of magn itude more than there are basepairs in the human genome. Each neuron i s connected to other neurons by thousands of synapses, creating a dens e network of communicating neurons. Cell-recognition events between ne urons at, and outside of synapses, are likely to guide the development and maintenance of the complex network formed by neurons. However, li ttle is known about which proteins are important for neuronal cell rec ognition. Neurexins, a family of polymorphic cell-surface proteins, mi ght mediate some of these cell recognition events. Thousands of neurex in isoforms are generated from three genes by usage of alternative pro moters and alternative splicing. These isoforms are displayed on the n euronal cell surface, with different classes of neurons expressing dis tinct combinations of isoforms. Neurexins probably have a multitude of ligands, some of which interact only with subsets of neurexin isoform s. This review describes the properties of the neurexin protein family and their potential roles in neuronal cell adhesion and intercellular signaling.