Mnx proteins promote MiP subtype identity and prevent interneuron-like and CaP-like processes. (A-D) Control and mnx MO-injected embryos. (A) In controls islet1 and islet2a expression is mutually exclusive at 18 hpf. (B) In embryos injected with mnx1, mnx2a, and mnx2b MOs, islet1 is co-expressed with islet2a in CaP and VaP. (C) Control embryos have normal, ventrally-projecting CaP axons (arrows) and dorsally-projecting MiP axons (arrowheads). (D) CaP axons (arrows) are normal in mnx MO-injected embryos whereas MiP axons (closed arrowheads) are absent and there are ectopic interneuron-like axons (open arrowheads). (E-J′′) Rhodamine-dextran-labeled MiPs in 28 to 32 hpf Tg(nrp1a:GFP) embryos injected with mnx1, mnx2a, and mnx2b MOs. Panels show rhodamine-dextran labeling (no superscript), nrp1a:GFP (2) and a merged image of the two channels (′′). Labeled MiPs (yellow arrowheads) become hybrids with six morphologies. (E-E′′) V2a hybrids express nrp1a:GFP and have a descending V2a-like axon. (F-F′′) MiP-V2a hybrids have a descending V2a-like axon as well as a normal-appearing MiP ventral axon; the red blob to the right is a cell that was killed during labeling. (G-G′′) MiP-V2a-CaP hybrids have a descending V2a-like axon as well as a ventrally-projecting CaP-like axon. (H-H′′) MiP-CaP hybrids have both a normal MiP axon and a CaP-like axon. (I-I′′) Truncated MiP-CaP hybrids have a truncated MiP dorsal axon as well as a ventrally-projecting CaP-like axon. (J-J′′) CaP hybrids have a CaP-like axon that extends next to a normal CaP axon. Scale bar: 20 μm, A-D; 40 μm, E-H′′.
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