The thrombospondin type 1 repeat (TSR) superfamily: Diverse proteins with related roles in neuronal development

The thrombospondins are a family of proteins found widely in the embryonic extracellular matrix. Like most matrix proteins, thrombospondins are modula r and contain a series of repeated domains arrayed between globular amino a nd carboxyl terminal domains. In recent years, other proteins that share th rombospondin type 1 repeats, or TSRs, have been identified. These include t he F-spondin gene family, the members of the semaphorin 5 family, UNC-5, SC O-spondin, and others. Most of these are expressed in the developing nervou s system, and many have expression patterns and in vitro properties that su ggest potential roles in the guidance of cell and growth cone migration, Bo th cell- and matrix-binding motifs have been identified in the TSRs of thro mbospondin-l, so it has been hypothesized that the properties of these dive rse proteins may also depend on the presence of these repeats. Here, are re view the cell biology of the TSR module, the extensive literature regarding the distribution and functions of thrombospondins and other TSR superfamil y proteins, and evaluate their possible roles during the development of the nervous system. Dev Dyn 2000;218:280-299. (C) 2000 Wiley-Liss, Inc.