Catarina Mrck1, Claes Axng2, Mattias Goksr3 and Marc Pilon2.
pha-2 is the C. elegans homolog of the vertebrate homeobox gene Hex. Embryonic expression of
pha-2 is mostly pharyngeal and the only described mutant allele of
pha-2 results in a severe pharyngeal defect in which certain muscle cells (
pm5 cells) and neurons are grossly deformed. Here we report a detailed characterization of the
pha-2 gene and phenotype using cell-type specific reporters, optical manipulation of the nuclei in pharyngeal muscle cells using optical tweezers, electron microscopy, staining of the actin cytoskeleton as well as phenotypic rescue and ectopic expression experiments. The main findings of the present study are: (i) The
pha-2 (
ad472) mutation specifically impairs the pharyngeal expression of
pha-2; (ii) In the
pha-2 mutant, the cytoskeleton of the
pm5 cells is measurably weaker and severely disrupted by large tubular structures and organelles; (iii) The
pm5 cells of the
pha-2 mutant fail to express the acetylcholinesterase genes
ace-1 and
ace-2; (iv) Ectopic expression of
pha-2 can induce ectopic expression of
ace-1 and
ace-2; and (v) Inhibition of acetylcholinesterase in a mutant with mislocalized
pm5 cell nuclei can reproduce the deformed isthmus phenotype of the
pha-2 mutant.