触觉是由体感神经元和皮肤细胞的联合功能赋予的。这些细胞通过由基底层填充的间隙相遇,在后生动物中发现的古老结构。使用秀丽隐杆线虫,我们研究了表皮和触摸受体神经元(TRN)界面的细胞外基质的组成和超微结构。我们证明含有层粘连蛋白的膜-基质复合物,Nidogen,MEC-4机电转换通道位于该界面处,并且是正确触感的中心。有趣的是,这些复合物的尺寸和间距与连续截面透射电子显微照片中观察到的不连续束状细胞外基质结构相对应。这些复合物无法在触摸不敏感的细胞外基质突变体和解离的神经元中合并。巢蛋白的损失降低了机械感受器复合物的密度和它们携带的触摸诱发电流的幅度。因此,神经元-上皮细胞界面在机械感觉复杂的组装和功能中起重要作用。与覆盖咽部和体壁肌肉的基底层不同,nidogen沿TRN募集到puncta不依赖于层粘连蛋白结合。MEC-4,但不是层粘连蛋白或nidogen,由细胞外基质成分的C末端Kunitz结构域中的点突变不稳定,MEC-1.这些发现表明,体感神经元分泌的蛋白质会积极地重新利用基底层,以产生负责振动触觉感知的特殊用途的机械感觉复合物。
The sense of
touch is conferred by the conjoint function of somatosensory neurons and skin cells. These cells meet across a gap filled by a basal lamina, an ancient structure found in metazoans. Using Caenorhabditis elegans, we investigate the composition and ultrastructure of the extracellular matrix at the epidermis and
touch receptor neuron (TRN) interface. We show that membrane-matrix complexes containing laminin, nidogen, and the MEC-4 mechano-electrical transduction channel reside at this interface and are central to proper
touch sensation. Interestingly, the dimensions and spacing of these complexes correspond with the discontinuous beam-like extracellular matrix structures observed in serial-section transmission electron micrographs. These complexes fail to coalesce in
touch-insensitive extracellular matrix mutants and in dissociated neurons. Loss of nidogen reduces the density of mechanoreceptor complexes and the amplitude of the
touch-evoked currents they carry. Thus, neuron-epithelium cell interfaces are instrumental in mechanosensory complex assembly and function. Unlike the basal lamina ensheathing the pharynx and body wall muscle, nidogen recruitment to the puncta along TRNs is not dependent upon laminin binding. MEC-4, but not laminin or nidogen, is destabilized by point mutations in the C-terminal Kunitz domain of the extracellular matrix component, MEC-1. These findings imply that somatosensory neurons secrete proteins that actively repurpose the basal lamina to generate special-purpose mechanosensory complexes responsible for vibrotactile sensing.