Figure 2.

Dorsal and Ventral RGCs Exhibit Homo- and Heterotypic Axon-Axon Contact Recognition

(A) Schematic of the retinotectal projection in Xenopus embryo. Time-lapse imaging of the OT was done from the indicated lateral view.

(B1–B3) An example of each observed in vivo axon-axon response is showed first as an initial acquired large field, followed by a time-lapse sequence at high magnification. The position of the ventral (VOT) and dorsal (DOT) optic tract is indicated. (B1) RGC growth cone (GC) crossing the encounter axon shaft. (B2) RGC GC tracking along the encounter axon shaft by multiple filopodia contacts (yellow arrows). (B3) RGC GC growing on the encounter axon, leading to the fasciculation of the two axon shafts (yellow arrowheads).

(C) Quantification of the axon-axon responses observed in the optic tract.

(D) Assay used to monitor axon-axon interactions in vitro.

(E and F) Examples of fasciculation (E) and crossing (F) events observed during homotypic interactions.

(G and H) Examples of tracking (G) and retraction (H) events observed during heterotypic interactions.

(I) Quantification of the global homotypic and heterotypic responses.

(J) Quantification of the axon-axon responses relative to the RGC topographic origin. Time stamps are in the format of min:s. ^∗p < 0.05, ^∗∗∗p < 0.001 (chi-square test for I and J). Numbers of events analyzed are indicated on the graph (n = 21 independent experiments).

Scale bars: 10 μm (B) and 5 μm (E–H).