Fig. 6

Lam1 Contact Is Sufficient to Transform a Neurite into an Axon In Vivo

(A) ath5:GAP-GFP transgenic, lamα1 morphant embryos were grown to 24 hpf, and Lam1-coated polystyrene beads were implanted into the retina of the right eye.

(B) Confocal reconstruction of an embryo that was implanted with a clump of 1 μM Lam1 beads and grown until RGC axons had extended (~3 dpf), immunostained with polyclonal anti-Lam1 antibody. This demonstrates the intimate association between the highly stained Lam1-coated beads and the extended axons. Axons hug the surface of the bead clump (arrow), causing the beads to lie within the axon fascicle.

(C) Time-lapse confocal imaging during axon extension demonstrates the dramatic interaction between polarizing RGC axons and the Lam1-coated beads (pseudocolored yellow), resulting in axon extension along the surface of the beads (visible growth cones marked by arrowheads) and bead engulfment by the axon fascicle (arrows).

(D) Highlighting an individual RGC by pseudocoloring it green demonstrates that after Lam1 bead contact (white arrows), the contacting neurite transforms into a process tipped with an elaborate growth cone that extends to form the axon, while the axon shaft remains associated with the bead (blue arrows).

Frames are taken from Movie S10. Lam1 Is Sufficient to Orient RGC Axon Extension In Vivo (Part 1) and [Movie S12. Lam1 Contact Transforms a Neurite into an Axon In Vivo]. Time is shown in hr:min; scale bars = 10 μM.