The function of Semaphorin on the neural network formation

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During embryogenesis, axons reach their specific targets correctly to form the complex neural network found in the mature functional nervous system. Several groups of axon guidance molecules such as semaphorins, ephrins, netrins, and slits have been reported to repel or attract the growing axons that express their cognate receptors. Semaphorin gene family contains a large number of secreted and transmembrane proteins, and some of them are functioning as the repulsive and attractive cues of the axon guidance during development. I report a novel member of murine class 3 semaphorin genes, semaphorin 3G (Sema3G), mapped on the chromosome 14. In the adulthood, Sema3G is mainly expressed in the lung and kidney, and a little in the brain. Interestingly, in the adult rodent brain Sema3G is expressed only in the granular layer of the cerebellum, as determined by Northern blot and in situ hybridization analyses. I also found that Sema3G binds Neuropilin-2, but not Neuropilin-1, and induces the repulsion of sympathetic axons, but not dorsal root ganglion axons, indicating that Sema3G utilizes Neuropilin-2 as a receptor to repel specific types of axons.