Nervous system function relies on precise synaptic connections. A number of widely-conserved cell adhesion proteins are implicated in cell recognition between synaptic partners, but how these proteins act as a group to specify a complex neural network is poorly understood. Taking advantage of known connectivity in C. elegans, we identified and studied cell adhesion genes expressed in three interacting neurons in the mating circuits of the adult male. Two interacting pairs of cell surface proteins independently promote fasciculation between sensory neuron HOA and its postsynaptic target interneuron AVG: BAM-2/neurexin-related in HOA binds to CASY-1/calsyntenin in AVG; SAX-7/L1CAM in sensory neuron PHC binds to RIG-6/contactin in AVG. A third, basal pathway results in considerable HOA-AVG fasciculation and synapse formation in the absence of the other two. The features of this multiplexed mechanism help to explain how complex connectivity is encoded and robustly established during nervous system development.

神经系统功能依赖于精确的突触连接。许多广泛保守的细胞粘附蛋白与突触伙伴之间的细胞识别有关，但是人们对这些蛋白如何作为一个组来指定一个复杂的神经网络知之甚少。利用秀丽隐杆线虫的已知连接性，我们确定并研究了成年男性交配回路中三个相互作用神经元中表达的细胞粘附基因。两个相互作用的细胞表面蛋白对独立地促进感觉神经元HOA与突触后靶标间神经元AVG之间的束缚：HOA中的BAM-2 /神经毒素相关蛋白与AVG中的CASY-1 /钙调蛋白结合。感觉神经元PHC中的SAX-7 / L1CAM与AVG中的RIG-6 / contactin结合。第三种基础途径在没有其他两种途径的情况下会导致大量的HOA-AVG束缚和突触形成。这种多路复用机制的功能有助于解释在神经系统发育过程中如何编码和牢固建立复杂的连接性。