Figure 3. CEH-12 is the nematode HB9 homolog, is expressed in VB motor neurons, and specifies VB fate. (A) Phylogenetic tree comparing members of the Mnx/HB9, UNC-4, and Even-skipped homeodomain transcription factor families. CEH-12 is more closely related to members of the Mnx family than to other C. elegans homeodomain proteins. (B) Genomic structures of Mnx family homeodomain genes. CEH-12 contains a homeodomain (70% identical to other species) and conserved N-terminal eh-1 Groucho interaction domain. (C) A promoter-GFP reporter,
ceh-12::GFP, is expressed in all 11 VB motor neurons and in a single head neuron, RID; occasional weak GFP expression was observed in the pharyngeal/intestinal valve cell and in the excretory gland cell (data not shown). (D) Structure of
ceh-12::GFP and
ceh-12 deletion alleles.
ceh-12::GFP was constructed using 2.8 kb of promoter sequence upstream of the predicted start site. The
gk391 allele deletes 0.5 kb of
ceh-12, including the predicted start site. The
tm1619 allele is a 1.1-kb deletion that removes the start site and most of the homeodomain. Both alleles are predicted null mutations. (E, top) Immunostaining reveals VAB-7 expression in DB and VC motor neurons in wild-type adult animals. (Bottom) VAB-7 is detected ectopically in VB motor neurons in
ceh-12(
gk391) mutant adult. Similar results are seen with
ceh-12(
tm1619) (data not shown). Bars: C,E, 10 μm.