Determination if the TS mutations are potentially fast-acting.

1We determined if an allele was potentially fast-acting in the following manner: We mounted embryos produced at 15°C on microscope slides and immediately made time-lapse videomicrographs at a room maintained at 24°C. If defects similar to those observed after long temperature shifts were found in at least 20% of the embryos and if there was little embryonic lethality at 15°C, we conclude that the allele may be fast-acting. We have labeled these cases as “Yes”. However, if there was significant embryonic lethality at 15°C, we cannot conclude that the presence of cellular defects after short upshifts is due to the upshift or to defects that occur even at 15°C. We have labeled these cases as “Unclear”.2For mei-1, par-2, and zyg-1, we incubated mutant worms at 26°C for 30 minutes prior to imaging (instead of the usual∼1 min. upshift) because the gene products appeared to be required prior to when we started our imaging (pronuclear migration).3High lethality at the permissive temperature precludes making a determination.4The low penetrance of severe defects precludes making a determination.