Arber S, Caroni P
Friedrich Miescher Institute, Basel, Switzerland.
J Cell Biol. 1995 Nov;131(4):1083-94. doi: 10.1083/jcb.131.4.1083.
Extracellular matrix (ECM) molecules are involved in multiple aspects of cell-to-cell signaling during development and in the adult. In nervous system development, specific recognition processes, e.g., during axonal pathfinding and synaptogenesis involve modulation and signaling by ECM components. Much less is known about their presence and possible roles in the adult nervous system. We now report that thrombospondin-4 (TSP-4), a recently discovered member of the TSP gene family is expressed by neurons, promotes neurite outgrowth, and accumulates at the neuromuscular junction and at certain synapse-rich structures in the adult. To search for muscle genes that may be involved in neuromuscular signaling, we isolated cDNAs induced in adult skeletal muscle by denervation. One of these cDNAs coded for the rat homologue of TSP-4. In skeletal muscle, it was expressed by muscle interstitial cells. The transcript was further detected in heart and in the developing and adult nervous system, where it was expressed by a wide range of neurons. An antiserum to the unique carboxyl-terminal end of the protein allowed to specifically detect TSP-4 in transfected cells in vitro and on cryostat sections in situ. TSP-4 associated with ECM structures in vitro and in vivo. In the adult, it accumulated at the neuromuscular junction and at synapse-rich structures in the cerebellum and retina. To analyze possible activities of TSP-4 towards neurons, we carried out coculture experiments with stably transfected COS cells and motor, sensory, or retina neurons. These experiments revealed that TSP-4 was a preferred substrate for these neurons, and promoted neurite outgrowth. The results establish TSP-4 as a neuronal ECM protein associated with certain synapse-rich structures in the adult. Its activity towards embryonic neurons in vitro and its distribution in vivo suggest that it may be involved in local signaling in the developing and adult nervous system.
细胞外基质（ECM）分子在发育过程和成年期的细胞间信号传导的多个方面发挥作用。在神经系统发育过程中，特定的识别过程，例如在轴突导向和突触形成过程中，涉及ECM成分的调节和信号传导。而关于它们在成体神经系统中的存在及其可能的作用，我们所知甚少。我们现在报告，血小板反应蛋白-4（TSP-4），TSP基因家族最近发现的成员，由神经元表达，促进神经突生长，并在成年期积聚在神经肌肉接头和某些富含突触的结构处。为了寻找可能参与神经肌肉信号传导的肌肉基因，我们分离了去神经支配后在成年骨骼肌中诱导表达的cDNA。其中一个cDNA编码大鼠TSP-4的同源物。在骨骼肌中，它由肌肉间质细胞表达。该转录本在心脏以及发育中和成年的神经系统中也被进一步检测到，在这些组织中它由多种神经元表达。针对该蛋白独特羧基末端的抗血清能够在体外转染细胞和原位冰冻切片上特异性检测TSP-4。TSP-4在体外和体内均与ECM结构相关联。在成年期，它积聚在神经肌肉接头以及小脑和视网膜中富含突触的结构处。为了分析TSP-4对神经元可能的活性，我们用稳定转染的COS细胞与运动神经元、感觉神经元或视网膜神经元进行了共培养实验。这些实验表明TSP-4是这些神经元的优选底物，并促进神经突生长。这些结果确立了TSP-4作为一种与成年期某些富含突触的结构相关联的神经元ECM蛋白。它在体外对胚胎神经元的活性及其在体内的分布表明，它可能参与发育中和成年神经系统中的局部信号传导。
