pha-2 was iolated in 1993 by Leon Avery in a screen for worms with visible defects in pharyngeal feeding behaviour. Worms in this strain exhibits morphological defects in muscles that form the isthmus and the terminal bulb. Many of the worms arrest as L1 and escapers grow slowly. We have recently cloned the gene and found that
pha-2 encodes the homeobox gene M6.3 which is most related to the vertebrate haematopoietic homeobox gene, hex. hex is one of the earliest known marker for anterior visceral endoderm and is involved in anterior-posterior axis formation and in the development of organs such as liver, lungs, thyroid and forebrain. We have sequenced the only existing allele (
ad472) and discovered that a point mutation in exon 2 introduces a stop codon such that it should only produce a short truncated protein without a homeodomain. The allele
ad472 is thus likely a null allele. To identify
pha-2 expressing cells we have made a pPHA-2::GFP reporter *. Our preliminary results indicates that the gene is only expressed in I4, an interneuron, of which the cell body is located in the terminal bulb and which sends out two axons through the isthmus and into the metacorpus. We are currently trying to identify genetic interactors and in particular will investigate if
pha-2 regulates or is regulated by
pha-4,
ceh-22 and
myo-2. * in which 2.7 kb of 5UTR from
pha-2 was used to drive GFP expression