Figure 1. Vulval development of C. elegans and lineage defect of bed-3 mutants.

A. Arrangements of Pn.p descendant cells through three rounds of division. Ovals represent cell nuclei. First two divisions occur in anterior/posterior orientation and produce a linear array of twelve Pn.p granddaughters. The twelve cells then divide in sublineage-specific orientations (indicated by letters below: L = longitudinal (a/p), T = transverse (l/r), U = undivided). Letters A through F represent cell types produced by each Pn.p granddaughter, vulA through vulF. In general, the third round of cell division produces two cells of the same type, thus each of the twelve Pn.p granddaughters corresponds to a single cell type. The only exceptions are the cells marked by the letter "B". These divide to produce vulB1 and vulB2 cells, which exhibit distinct gene expression patterns. B. The wild-type vulval cell divisions represented as a lineage diagram. The time is plotted on the vertical axis, and markers on the left are at one hour intervals. Each branching of the inverted tree figure represents a cell division. The orientation of the terminal division is marked below each sublineage. Cells are referred to by their ancestry: The posterior daughter of P5.p is P5.pp. The anterior daughter of P5.pp is P5.ppa and so on. We use x(e.g. P5.ppx) to refer to an unspecified daughter cell, and Pn.p refers to P5.p, P6.p or P7.p. C. Top: Lineage diagrams of representative bed-3(sy644) and bed-3(sy705) mutant animals. Observations were initiated after the completion of the first two rounds of Pn.p divisions and continued until several hours after the last division. Bottom: Lineage diagrams of representative cye-1(eh10) and bed-3(sy705) animals. Observations were started before the first Pn.p division and stopped after the second round of division. Whether these cells had divided further was not determined. The observed portion of the lineage is marked by black lines. Grey lines represent portions of the lineage that were inferred based on cell size and position. The time of molting is indicated by a horizontal line across the lineage diagram. Molting was not scored in the bed-3(sy644) animal, and probably took place after all divisions were completed.