Figure 3.

Glycoproteins with special roles in the nervous system. These three proteins are involved in synapse formation (Agrin) and in axonal guidance (Slits and Netrins). Sites for binding other ECM proteins (laminins), growth factors, and cell-surface receptors (α-dystroglycan and MuSK) are indicated for agrin. Slit also contains known GF-binding domains (Foln). Agrin has two small alternatively spliced exons that markedly affect its functions, a characteristic of many ECM proteins. Unlike many ECM proteins, the major receptors for these three proteins are not integrins. Slit family proteins bind to Robo receptors, whereas Netrins bind to Unc5 and DCC receptors. The functions of these ECM-receptor pairs in the CNS are discussed in Barros et al. (2011) but they also function in other aspects of cell and tissue pattern regulation during development. They are evolutionarily ancient and are conserved in all bilaterial phyla.