Worm Breeder's Gazette 9(3): 102
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.
The cell lineage of a wild-type worm results in two kinds of cells:
live ones, which survive long enough to function, and dead ones, which
die shortly after they are born. Ellis and Horvitz (Cell 44: 817-829,
1986) showed that almost all programmed cell deaths are prevented by
mutations in the gene ced-3, so that in ced-3 worms, dead cells are
converted to undead. They also showed that dead cells can have hidden
fates, and that ced-3 mutations can reveal these hidden fates, so that
undead cells take on some differentiated characteristics of closely
related cells. We wanted to find out if a cell that ordinarily dies
during wild-type development could become a functional neuron.
We used a laser microbeam to show that the pharyngeal neuron M4 is
essential for normal feeding. The first line of the table shows the
data. When M4 was killed in a newly hatched larva, the worm couldn't
swallow food and therefore starved. The front halves of the pharynxes
of arrested worms were always stuffed with bacteria, the result of the
loss of posterior isthmus function that happens when M4 is killed.
Work described in the last WBG showed that this syndrome is produced
only by loss of M4 function. Unfortunately, almost 40% of the worms
crawled off the agar, never to be seen again. Because we were worried
about these lost worms, we did some operations in unc-54(e190) and cha-
1(p1152) worms, which are unable to crawl away as quickly as wild-type.
The mutations reduced the frequency of loss, and M4 proved essential
in these genotypes as in wild-type.
In about half of ced-3 worms there are two cells, M4(a) and M4(p),
where one sees only M4 in wild-type. The last four lines of the table
show the results of experiments we did to determine whether the undead
cell (which we suspect is MSpaaaaap, the posterior sister of M4) can
replace M4.
Intact ced-3 worms always had full M4 function. (Intact refers to a
worm that has not been operated on.) The table shows data on 20 worms
that were followed in detail. Some intact ced-3 worms arrest as eggs,
larvae, or stunted adults, but none of these stuff, so we believe
their problems have nothing to do with M4. (Ellis and Horvitz also
noticed that MT1522 ced-3(n717) worms are less healthy than wild-type,
possibly due to a linked mutation.) None of the many intact ced-3
worms we've looked at in the course of other experiments has stuffed. (
In fact, we have never seen intact worms of any genotype stuff.)
When we killed M4(p), almost all worms had full M4 function. When we
killed M4(a), almost no worms had full M4 function. The simplest
interpretation is that in most ced-3 worms, M4(a) is M4. Unexpectedly,
40-50% of the worms in which M4(a) was killed had partial M4 function.
These worms were clearly distinct from both the arrested larvae
characteristic of total lack of M4 function, and the normal adults
characteristic of full M4 function. The last line of the table shows
that this partial M4 function is due to M4(p). When both M4(a) and M4(
p) are killed, ced-3 worms have no M4 function. We conclude that a
cell that dies during normal wild-type development, M4(p) (probably
MSpaaaaap), can have some M4 function in ced-3.{Figure
1}
Unless otherwise noted, operated worms were checked one day after
the operation to make sure that the desired nuclei had been killed,
and that there was no other damage visible using Nomarski optics. Lost
means that the worm was lost within three days after hatching. Larva
means that the worm never became an adult. (Worms were followed until
they died or were lost.) Stunted adult means that the worm took longer
than normal to reach adulthood, was small, and looked starved. Normal
means that the worm was indistinguishable from an intact wild-type
worm. Unless otherwise noted, worms in the larva and stunted adult
classes stuffed, indicating a deficit in M4 function. Normal worms
never stuffed. Blank positions are zeroes.
a Only 17 of the 62 animals in this row were checked for successful
operation. Seven were lost; the other ten stuffed and arrested as
b These two worms did not stuff. They are discussed in the text.
c One of these two worms did not stuff.
d This worm made a vulva after 10 days, but did not produce any
progeny.