title: HAIRY-like transcription factors and the evolution of the nematode vulva equivalence group.
abstract: BACKGROUND
  Nematode vulva formation provides a paradigm to study the evolution of pattern formation and cell-fate specification. The Caenorhabditis elegans vulva is generated from three of six equipotent cells that form the so-called vulva equivalence group. During evolution, the size of the vulva equivalence group has changed: Panagrellus redivivus has eight, C. elegans six, and Pristionchus pacificus only three cells that are competent to form vulval tissue. In P. pacificus, programmed cell death of individual vulval precursor cells alters the size of the vulva equivalence group.
  
  
  RESULTS
  We have identified the genes controlling this cell-death event and the molecular mechanism of the reduction of the vulva equivalence group. Mutations in Ppa-hairy, a gene that is unknown from C. elegans, result in the survival of two precursor cells, which expands the vulva equivalence group. Mutations in Ppa-groucho cause a similar phenotype. Ppa-HAIRY and Ppa-GROUCHO form a molecular module that represses the Hox gene Ppa-lin-39 and thereby reduces the size of the vulva equivalence group. The C. elegans genome does not encode a similar hairy-like gene, and no typical HAIRY/GROUCHO module exists.
  
  
  CONCLUSIONS
  We conclude that the vulva equivalence group in Pristionchus is patterned by a HAIRY/GROUCHO module, which is absent in Caenorhabditis. Thus, changes in the number, structure, and function of nematode hairy-like transcription factors are involved in the evolutionary alteration of this equivalence group.
authors.affiliation: Department for Evolutionary Biology, Max-Planck Institute for Developmental Biology, Tübingen, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Schlager
authors.forename: Waltraud
authors.initials: W
authors.lastname: Röseler
authors.forename: Min
authors.initials: M
authors.lastname: Zheng
authors.forename: Arturo
authors.initials: A
authors.lastname: Gutierrez
authors.forename: Ralf J
authors.initials: RJ
authors.lastname: Sommer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D005075:Biological Evolution; D017173:Caenorhabditis elegans / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018257:Helix-Loop-Helix Motifs; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009348:Nematoda / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D016415:Sequence Alignment; D014844:Vulva / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D015801:Helminth Proteins; D018398:Homeodomain Proteins; D012097:Repressor Proteins