Fig. 7. Interactions among NgCAM, contactin 4 and APPs in RGC axon outgrowth. Retinal strips cultured on different substrates before axon imaging. (A-D) APPs and APP(18-205) both enhanced outgrowth on NgCAM. AP, n=12; other conditions, n=6. (E) APPs enhanced NgCAM-dependent, but not laminin-dependent, axon outgrowth. n=6. (F) Contactin 4-Fc inhibitied NgCAM-dependent, but not laminin-dependent, axon outgrowth. n=10. Protein coating was varied in different experiments; the high basal outgrowth here allowed for robust quantitation of the inhibitory effect of contactin 4-Fc. (G-K) Contactin 4 shRNA in replication-competent retrovirus inhibited axon outgrowth on NgCAM+AP-APPs, but not on laminin. Laminin, n=11 (shRNA), n=11 (control virus); NgCAM+APPs, n=21 (shRNA), n=19 (control virus). (L) Model of APPs, NgCAM and contactin 4 function based on the assays of RGC axon outgrowth shown here. Other cis and trans interactions might also occur. See text for details. ^*, P<0.025 by Student's t-test. Error bars, s.e.m. Scale bars: 300 µm.