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Fig. 1. Cell fate transformations in the T.pp lineage in sem-4 animals.
Lineage diagrams of the wild-type T.pp, AB.p(l/r)apappp and QL lineages (top)
and the variable T.pp lineage in sem-4 animals (bottom). Cell deaths
are indicated with an `X'. Cells in parentheses exhibit abnormal morphologies
or migration patterns. Cells that expressed the mec-3::gfp reporter
are indicated with a `mec-3'. The proportion of sem-4
animals in which T.pp adopted each fate (only one side was examined per
animal) is shown beneath the lineage diagrams. Of the 18 animals in which
T.ppa did not divide, T.ppa died in nine and lived in nine. In four out of 23
animals, T.ppa divided and gave rise to an anterior daughter that died and a
posterior daughter that migrated ventrally and then began to express
mec-3::gfp. In a fifth animal, T.ppa divided and the posterior
daughter migrated to the ventral side but the worm died before the lineage was
completed. While examining these lineages, we found that loss of
sem-4 function not only induced apoptosis in a cell that should
normally differentiate (T.ppa), but also sometimes induced deaths that
appeared to be necrotic, both in T.ppa and in a cell that normally undergoes
apoptosis (T.pppp). These necrotic deaths were characterized by the formation
of large vacuoles, similar to those induced by gain-of-function mutations in
degenerin genes (Chalfie and Wolinsky,
1990 ; Hall et al.,
1997). T.pppp died as a vacuolated cell in one of the five
lineages in which T.ppa divided and in two of the nine lineages in which T.ppa
lived; in all nine lineages in which T.ppa died, T.pppp underwent apoptosis.
T.ppa itself died as a vacuolated cell in three out of nine lineages. The
egl-5 gene was ectopically expressed both in cells undergoing
apoptosis and in cells undergoing necrosis in sem-4 animals.
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100gfp in
wild-type animals. PV6CREgfp in wild-type animals shows
only occasional, faint T lineage expression (top). Scale bar: 10 µm. Arrows
indicate T.pa and T.pp cells expressing GFP. (D) Binding to V6CRE. The
addition of SEM-4 to radiolabeled probe produced two complexes (arrows).
Binding decreased substantially in the presence of 100-fold molar excess of
cold specific competitor. Mutation of e5-4 and e5-5 as indicated in the
specific competitor restored binding of complexes 1 and 3. Mutation of e5-T1
as indicated did not restore binding. Mutation of e5-4, e5-5 and e5-T1
produced the same restoration of binding as mutation of e5-4 and e5-5.
3 kb upstream of the
egl-5 ATG fused to the gfp gene. Arrows indicate PLM (left)
and PLM and T.pppaa (right). The same ectopic expression was observed in
sem-4 animals with an egl-5::gfp reporter containing 12 kb
upstream of the egl-5 ATG fused to the gfp gene. Scale bar:
10 µm.
