Rj. Sommer et Pw. Sternberg, APOPTOSIS AND CHANGE OF COMPETENCE LIMIT THE SIZE OF THE VULVA EQUIVALENCE GROUP IN PRISTIONCHUS-PACIFICUS - A GENETIC-ANALYSIS, Current biology, 6(1), 1996, pp. 52-59
Background: To understand how alterations in the molecular mechanisms
underlying developmental processes generate a diversity of biological
forms, comparative developmental biology can be combined with genetic
analysis. The formation of the nematode vulva is one tractable system
for such evolutionary developmental analysis, as much is understood ab
out its development in Caenorhabditis elegans. In Caenorhabditis, six
of twelve ventral epidermal cells form the 'vulva equivalence group';
although all six cells are competent to adopt vulval cell fates in res
ponse to an inductive signal, only three of these cells are induced to
form vulval tissue. Results: In some species of the nematode families
Rhabditidae, Neodiplogastridae and Panagrolaimidae, the number of cel
ls in the vulva equivalence group is limited by apoptosis and decrease
d responsiveness to inductive signals (competence). We have initiated
a genetic analysis in one of these species, Pristionchus pacificus, to
understand the evolution of the specification of ventral epidermal ce
lls that are competent to generate the vulva. A ped-4 mutation restore
s competence to an incompetent cell. Mutation of either of two other g
enes of Pristionchus cause two anterior cells that die in wild-type to
survive. A ped-5 mutation causes these cells to be competent to respo
nd to inductive signals, expanding the equivalence group. A ped-6 muta
tion causes these cells to form ectopic, anterior vulva-like invaginat
ions. Conclusions: During nematode evolution, apoptosis and change of
competence alter the number and potency of ventral epidermal cells. Th
e phenotypes of Pristionchus mutants suggest that alterations in homeo
tic gene control of anteroposterior patterning is involved in creating
this cellular diversity.