Figure 6.

Differential subcellular targeting of DAGLα and MGL during axon development. A, A₁, In primary cortical cultures, DAGLα and MGL are cotargeted to growing axons and often coexist in stable varicosities (B, arrowheads). During axon fasciculation (C) and postsynaptic targeting (D), DAGLα (Bisogno et al., 2003) but not MGL (arrowheads) is eliminated from axons and presynapses. D₁, VAMP2 (synaptobrevin 2) was used to visualize presynaptic specializations. E, MGL is selectively trafficked into the quiescent premature axon (a) and accumulates in its proximal segment as soon as neuronal polarization commences. In neurites with looped growth cones (E₁), fluorescence signal separation reveals mutually exclusive distribution of actin and MGL in motile axons (a; open rectangle) or dendrites (d). E₂, MGL microgradients are invariably present in coexisting neurites with bundled (gc₁), spread (gc₂), or looped (gc₃) growth cones. E₃,E₃′, The presence of MGL in established axon segments and presynapse-like varicosities (arrows) is maintained in elaborate axonal meshworks in vitro. F, F₁, Subcellular MGL and DAGLα targeting is strikingly different, with MGL being primarily excluded from the motile neurite tip (arrow). Arrowheads indicate the transition point between MGL⁺ and MGL⁻ domains. G, MGL immunofluorescence intensity measured in individual bundled/spread (left) or looped (right) growth cones (gcs) and adjoining distal axon segments. Individual fluorescence intensity plots are in gray, and average values are in blue/red. Scale bars: A–C₁, D₁, F–G₁, 10 μm; E, 3 μm.