Cell-cell recognition, fusion, migration and rearrangements are processes involved in organ formation and patterning. In C. elegans these have been reported to occur in the formation of the hypodermis, uterus, excretory gland cells, pharynx and vulva. Cell migrations and fusions during vulval development were characterized using immunofluorescence techniques and confocal microscopic reconstructions. Vulval sections at different times during the developmental process were stained for MH27, an adherens junction protein (1). Events have been followed from the time the fates of the six vulval precursor cells (VPCs) have been specified through inductive signalling by the anchor cell to the construction of a tube that consists of seven toroidal rings stacked together (a total of 20 hr.). These rings are designated as: vulA, vulB1, vulB2, vulC, vulD, vulE and vulF (2,3). Early morphogenesis involves generation of the VPC daughters, VPC grand-daughters and great-granddaughters, which results in 22 epithelial cells forming a vulva primordium. These cells are more or less arranged in a two dimensional fashion. Later, these cells perform short range migrations from the outer regions towards the central midline of the developing vulva in a symmetrical fashion. They also undergo fusions with specific partners before they migrate, eg. precursors of vulA on either side of the primordium fuse in pairs before migrating. The cells adjacent to the innermost cells form processes and migrate around them. This is repeated in a temporal sequence by the next outer cells which send processes around their inner neighbours, which meet at the midline. These migrations push the inner ring precursors dorsally, forming an invagination. The final result is the formation of a stack of seven rings (vulA to vulF). This is followed by fusion between the component cells in each ring, the order of the intra-toroidal fusions being vulD,vulA, vulC, vulF and vulE. The anchor cell eventually penetrates the inner ring (vulF) and fuses with the uterine cell, utse (4). In the late L4 stage, the vulva is connected to the uterus by vulF and vulval muscles attach the vulva to the body wall and the uterus. In summary, vulval development involves specific migrations and fusions of the cells involved in a spatial and temporal order. Our preliminary studies on the Muv mutant
lin-15(
e1763) which has one !real! vulva and 2-3 !pseudovulvae! have shown early L4 worms where the vulval ring precursor cells have failed to migrate, and form ring-like processes around their inner neighbours thus failing to produce the stack of rings in the center. Further studies with this mutant and other Muv mutants will explain the mutant phenotype in terms of specific defects in migration and fusions of the cells involved. 1. Podbilewicz, B. and White, J.G. (1994). Dev.Biol. 161, 408-424. 2. White, J.G. Personal Communication. 3. Sharma-Kishore, R. and Podbilewicz, B. (1997).The Worm Breeders Gazette. Vol.15#1.
p58. 4. Newman, A.P., White, J.G. and Sternberg, P.W. (1996). Development 122, 3617-3626.