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doi: 10.1242/10.1242/dev.00570

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zag-1, a Zn-finger homeodomain transcription factor controlling neuronal differentiation and axon outgrowth in C. elegans

¹ Max Planck Institute for Medical Research, Jahnstr. 29, 69120 Heidelberg, Germany
² Johns Hopkins University, Department of Biology, 3400 North Charles Street, 21218 Baltimore, MD, USA

View larger version (49K): [in a new window]   Fig. 1. Cloning of zag-1. (A) Genomic region containing the zag-1 gene. The fraction of transgenic lines rescuing zag-1 defects is indicated with numbers beside the cosmid names (3/4 – defects were rescued in 3 out of 4 transgenic lines). `Cosmid pool' refers to a mixture of all the cosmids shown. (B) ZAG-1 protein sequence. Zn fingers are indicated in bold, the homeodomain is underlined, the CtBP1/2 corepressor binding site (PLDLT) is in bold italics and the star indicates the premature stop codon in rh315. (C) Sequence alignments of Zn fingers. The sequence of the Zn fingers in the chick EF1 protein is identical to human ZEB. (D) Domain organisation of ZAG-1 and its homologs. Zn fingers are indicated in black, homeodomains in dark grey, SMAD-interacting domain in light grey and CtBP1/2 corepressor binding sites are dashed vertical lines.

View larger version (130K): [in a new window]   Fig. 2. Expression of zag-1. zag-1::YFP: DIC (A-C) and corresponding epifluorescence images (D-F) of embryos at different developmental stages. zag-1 expression is mainly seen in neurons in the head and tail ganglia as well as in ventral cord motorneurons. Stars (F) mark two pharyngeal nuclei, probably m4 and m5 muscle cell nuclei. (G-H) Early (G) and late (H) L1 larvae; expression is seen transiently in postembryonic motorneurons (H). Arrowheads (H) indicate motorneuron nuclei in the ventral cord. Pzag-1::YFP in wildtype (I) and zag-1(rh315) animals (J-L); zag-1 expression in neurons is not downregulated in zag-1(rh315). Arrows (I,J,L) indicate intestinal muscle, arrowheads (I,J,L) indicate the anal depressor muscle. Ventral aspects in (I,J), side views in all others. Anterior is to the left, dorsal is up. Scale bars: 20 µm.

View larger version (90K): [in a new window]   Fig. 3. Neuronal defects in zag-1(rh315). Wild-type (A,C,E,G,I,K) and zag-1(rh315)-mutant animals (B,D,F,H,J,L) expressing glr-1::GFP (A-F), unc-47::GFP (G-J) and unc-4::GFP (K,L). zag-1(rh315) mutants have several axon outgrowth defects and misexpression of neuronal markers. Arrowheads (B,F) indicate cells ectopically expressing glr-1::GFP. Arrows (B) indicate lateral axons, (F) the PDB axon, which has a characteristic and unique trajectory, (H) a missing anterior commissure branch, and (J) a commissure growing on the wrong side. Ventral aspects in (C,D,I,J), side views in all others. Anterior is to the left, dorsal is up. Scale bars: 20 µm.

View larger version (129K): [in a new window]   Fig. 4. Mesodermal and neuronal defects in zag-1(hd16). (A,B) Wild-type and zag-1(hd16) larvae after 1 hour incubation with fluorescent latex beads. Fluorescent material was transported into the gut in wild type (A), but remained in the anterior part of the pharynx in zag-1 (B). zag-1(hd16) also has pronounced axon guidance defects. (C) zag-1(hd16) L1 larva expressing glr-1::GFP; the arrow indicates an axon extending laterally, arrowheads indicate ectopically expressing cells, and dotted lines indicate ventral cord defasciculation. (D) zag-1(hd16) L1 larva expressing unc-47::GFP; the arrows indicate commissures not reaching the dorsal cord but extending processes in a lateral position, arrowheads indicate gaps in the ventral cord, dotted lines indicate ventral cord defasciculation. Ventral aspect in C,D; side views in A,B. Anterior is to the left. Scale bars: 20 µm.