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A follower neuron is a nerve cell that arises in the developmental stage of the brain and which growth and orientation is intrinsically related to pioneer neurons. These neurons can also be called later development neurons or follower cells. In the early stages of brain development, pioneer neurons define axonal trajectories that are later used as scaffolds by follower neurons, which project their growth cones and fasciculate with pioneer axons, forming a fiber tract 〔Chédotal A and Richards LJ (2010). Wiring the Brain: The Biology of Neuronal Guidance. Cold Spring Harb Perspect Biol; 2:a001917.〕 and demonstrating a preference for axon-guided growth.〔Hidalgo A and Booth GE (2000). Glia dictate pioneer axon trajectories in the Drosophila embryonic CNS. Development, 127: 393-402.〕〔Raper J and Mason C (2010). Cellular Strategies of Axonal Pathfinding. Cold Spring Harb Perspect Biol; 2:a001933.〕 It is thought that these neurons can read very accurate cues of direction and fasciculate or defasciculate in order to reach their target, even in a highly dense axon bundle.〔 == Follower - pioneer interactions == The interactions between follower and pioneer axons can be of two types: isotypic, when the axons are from the same neuronal type; and heterotypic, when the axons are from different neuronal types and have different origins and targets. In the development of complex vertebrate nervous systems, axons usually have the same origin and target, so they can be guided by isotypic interactions.〔Pittman AJ, Law M-Y and Chien C-B (2008). Pathfinding in a large vertebrate axon tract: isotypic interactions guide retinotectal axons at multiple choice points. Development, 135: 2865-2871.〕 It has been assumed that pioneer neurons have an important role in guiding follower axons, being essential for them to reach their targets. However, the results about this role of pioneer neurons in specifying the projection path of follower axons are conflicting, once that some studies have been showing that pioneer neurons are not required or only facilitate the extending along follower neurons’ normal path.〔〔〔Takizawa K and Hotta Y (2001). Pathfinding analysis in a glia-less gcm mutant in Drosophila. Dev Genes Evol, 211: 30-36.〕〔Merianda TT, Botta V and Bhat KM (2005). Patched regulation of axon guidance is by specifying neural identity in the Drosophila nerve cord. Dev Genes Evol, 215: 285-296.〕 For example, studies in ''C. elegans'' and ''Drosophila'' developing embryos showed that the correct outgrowth of follower neurons is not dependent on pioneer neurons, instead they probably only give further cues to make sure that each axon is in the right axon tract.〔〔〔Hutter H, Wacker I, Schmid C, Hedgecock EM (2005). Novel genes controlling ventral cord asymmetry and navigation of pioneer axons in C. elegans. Developmental Biology, 284: 260-272.〕 There is even a study in zebrafish with results showing that, when pioneer axons are eliminated, they can be replaced by follower axons, which since then behave like pioneer ones.〔Bak M and Fraser SE (2003). Axon fasciculation and differences in midline kinetics between pioneer and follower axons within commissural fascicles. Development, 130: 4999-5008.〕 On the other hand, in invertebrates, pioneer neurons seem to have a central role in guiding follower neurons to their targets, because their removal leads to errors in follower neurons’ pathfinding.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Follower neuron」の詳細全文を読む スポンサード リンク
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