Failure to execute cross-midline divisions results in duplicated neuraxes in EphA4 and EfnB2a MO mosaics.
Immunostaining of 18 hpf mosaic embryos shown in dorsal view with anterior to the left. (A-C) merged images showing α-aPKC (green) and MO host cells labelled with rhodamine (red). (A) aPKC is expressed on the apical surface of neuroepithelial cells, which is at the midline. (B) WT EphA4+ cells (unlabelled) fail to cross the midline and form unilateral clusters in EphA4MO r3 and r5 (white arrowheads); these clusters have an ectopic aPKC+ apical region that is frequently perpendicular to the endogenous midline. Likewise WT EfnB2a+ cells form a unilateral cluster in r4 of an EfnB2a MO host (data not shown). (C) WT cells transplanted into an EphA4;EfnB2a double MO host form three separate clumps with ectopic apical surfaces (data not shown) or fuse to give rise to a partially duplicated neuroepithelium in the r3-r5 region; cell clustering is also sometimes evident in r7 (N=6). OV (otic vesicle). (E,F) α-laminin staining (left panels); right panel is a merge with the rhodamine-labeled double MO host cells (red). (E) Laminin is expressed along the lateral edges of the neuroepithelium in WT (not shown) and in double MO host embryos (N=24). (F) Laminin is ectopically expressed around the eges of the cluster of unlabeled WT cells in a WT to double MO mosaic embryo (N=27). Scale bars: 50μm.