Fig. 3.

Stabilization of Cytoneme Contacts. A Cytoneme stabilization through additive contact. Stability can be conferred by protein–protein interactions in trans. Cytoneme-localized transmembrane proteins can bind heparan sulfate proteoglycans (HSPGs) (green). For Hh (dark purple), HSPGs contribute to Ihog (blue) interactions in trans to stabilize cytoneme-cytoneme contacts (left). HSPGs in the ECM or on cytoneme membrane can also cooperate in the higher affinity Ihog–Hh interaction (center). Highest affinity interactions are achieved between the Ihog, ligand, and Hh receptor Ptc (orange) to allow for morphogen transfer and pathway activation. B Stability of cytoneme contact through CAMs. HH co-receptors BOC/Boi and CDON/Ihog also function as CAMs to stabilize these points of interaction. Dpp transport is supported by wing disc expression of CAM Capricious (Caps)/Tartan (Trn) and by ASP expression of neuronal CAMs Neuroligin 2 (Ngl2) and Neuroglian (Nrg) at cytoneme tips