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要旨:
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, the reduction of the vulva equivalence group is achieved by programmed cell death of individual precursor cells. 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 which 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. Instead, the size of the C. elegans vulva equivalence group is regulated by the EGF and WNT signaling pathways.
