Worm Breeder's Gazette 14(4): 43 (October 1, 1996)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Evolution of vulva formation: Part VIII: Changes of developmental mechanisms in the absence of changes in the cell lineage during the evolution of vulva formation in the Diplogastridae (Nematoda).

Ralf J. Sommer

MPI fuer Entwicklungsbiologie, Spemannstrasse 35, 72076 Tuebingen, Germany

Several aspects of cell fate specification during vulval development
differ between Caenorhabditis and Pristionchus. Two of the six cells
that correspond to the Caenorhabditis vulval equivalence group die by
programmed cell death in Pristionchus. Another cell fuses with the
epidermis early in development, making it incompetent to form vulval
tissue. A third evolutionary change of cell fate exists, as another cell
has only limited developmental potential and can adopt the 2o but not
the 1o fate. In Caenorhabditis, all six vulval precursor cells (VPCs)
are multipotent, i.e. they can adopt all three cell fates. Thus, in a
group of six cells, three evolutionary alterations of cell fate
specification occurred between the two species.
        To determine if the observed changes of cell fate specification
between Pristionchus and Caenorhabditis evolved independently, species
of six additional genera of the Diplogastridae have been studied.
Comparative studies of cell lineage and pattern formation during vulval
development in the species Diplogaster maupasi, Koerneria sp.,
Diplogasteroides sp., Pseudodiplogasteroides sp., Aduncospiculum halicti
and Goodeyus ulmi have been carried out. All species display an
identical differentiation pattern of ventral epidermal cells as revealed
by cell lineage analysis. Despite these morphological similarities, cell
ablation experiments suggest differences in the underlying pattern
formation processes. In four species (Koerneria, Diplogasteroides,
Pseudodiplogasteroides and Aduncospiculum), the cell (P7.p) that has
limited developmental potential in Pristionchus, can adopt either vulval
cell fates. In two species (Koerneria and Diplogasteroides), P8.p, the
cell that is incompetent in Pristionchus, is competent in a manner
similar to the corresponding cell in Caenorhabditis. Furthermore, in
Diplogaster and Goodeyus, some VPCs show differentiation properties in
the absence of gonadal inductive signal. The finding that the pattern of
cell competence varies among species indicates that developmental
mechanisms can change during evolution while differentiation pattern
remain invariant.