The N-terminal extracellular domains of TM-agrin are required to induce BRF formation in COS7 cells. Cells were transfected with GFP-tagged TM-agrin (A), TM-N agrin, lacking the C-terminal domains (B), or TM-C agrin, lacking the extracellular N-terminal domains (C) and immunostained with GFP antibodies. TM-N agrin induced BRFs to a lesser extent than TM-agrin, but TM-C agrin did not induce BRFs.