Figure 3. SKN-1 distribution in
par-1,
par-2,
par-3 and
par-4 mutant embryos. Fluorescence micrographs showing fixed 4-cell-stage wild-type and par mutant embryos stained for SKN-1 protein (left column) and with DAPI to visualize DNA in nuclei (right column). Embryos are oriented with anterior to the left as determined by the position of DAPI-stained polar bodies (visible in I and J; out of the focal plane in the other DAPI images). (A,F) Wild-type embryo with high levels of SKN-1 in P2andEMS. Lower levels are just detectable in ABa and ABp. Note that the chromosomes are more highly condensed in ABa and ABp than in P2and EMS. In DAPI-stained par mutant embryos (G-I),chromosome condensation appears equivalent as all four cells divide synchronously. (B,G)
par-1(2012) mutant embryo. In 22/24 4-cell-stage
par-1 embryos, equal levels of staining were detected in all blastomeres; in 2/24 embryos, slightly lower levels of SKN-1 were detected in the two more anterior blastomeres. Similar results were obtained with
par-1(
b274) embryos (data not shown). (C,H)
par-2(
lw32) mutant embryo. In 10/13 4-cell-stage
par-2 embryos, SKN-1 was detectable in the two most posterior blastomeres and undetectable or barely detectable in the two most anterior blastomeres; in 3/13 slightly lower levels of SKN-1 were detected in the two more anterior blastomeres. Similar results were obtained using
par-2(
it5ts) embryos (data not shown). (D,I)
par-3(
it71) mutant embryo. In 8/14 4-cell-stage
par-3 mutant embryos, SKN-1 was evenly distributed; in 3/14, one 4-cell-stage blastomere stained less brightly than the other three; in 2/14, the two anterior blastomeres stained less brightly; in 1/14, the two posterior blastomeres stained less brightly. In all cases, SKN-1 was distributed more evenly than in wild-type. Similar results were obtained using
par-3(
it62) embryos (data not shown). (E,J)
par-4(
it57) mutant embryo. In 9/11 4-cell-stage
par-4 mutant embryos, high levels of SKN-1 were present in the two smaller posterior blastomeres with no or little SKN-1 detectable in the two larger anterior blastomeres; in 2/11 nearly equal levels of SKN-1 were detected in all four blastomeres. As in wild-type embryos, SKN-1 was detectable at low levels in all 2-cell-stage and 4-cell-stage par mutant embryos examined [n=18, 8, 16, and 14 for
par-1,
par-2,
par-3 and
par-4 mutant embryos, respectively]. SKN-1 was detectable in some but not all 8-cell-stage mutant embryos: 4/18
par-1, 2/9
par-2, 3/14
par-3 and 2/7
par-4 embryos had detectable staining, frequencies similar to wild-type (Bowerman et al., 1993). In all embryos, SKN-1 was not detectable by the 16-cell stage (data not shown).