Deletion of 3 nucleotides leading to a deletion of Serine 241 (which is within an alpha-helix in the third Arm repeat).
Embryos maternally mutant for Apc2ΔS exhibit a weak actin pseudocleavage furrow extension defect that is apparent only at a depth of 2.2 micrometer from the surface.
58% of Apc2ΔS maternally mutant syncytial embryos show movement of over 2% of cortical nuclei into the embryo interior, compared to 0-3% of wild-type embryos. Furthermore, 21% of embryos from Apc2ΔS/+ mothers show this phenotype.
The cuticle of an average Apc2ΔS maternal/zygotic embryo shows an anterior hole, is 50-60% the length of wild-type and has 2-3 patches of denticles remaining. This cuticle phenotype is less severe when embryos are raised at 180C.
Asymmetric divisions appear to be unaffected in the brains of mutant larvae.
Apc2ΔS is temperature sensitive but even at the restrictive temperature it is homozygous viable in the first generation. Homozygous mutant flies mated to each other will produce 100% lethal embryos, all showing the excess naked cuticle typical of ectopic wg pathway activity. At 18o, the homozygous mutant (maternal/zygotic) embryos are essentially wild-type and the flies can be maintained as a homozygous stock. The phenotype at restrictive temperature is not equivalent to a null phenotype.
Embryos derived from homozygous parents show residual denticle bands.
Nuclei migrate to the cortex normally in syncytial homozygous embryos derived from homozygous female germline clones, but then many nuclei are lost from the cortex into the internal cytoplasm. When spindles and chromosomes are lost from the surface, centrosomes remain behind and continue to organise pseudocleavage furrows and actin caps. Overall spindle morphology and astral microtubules appear normal during early peripheral divisions, but during later peripheral divisions, spindles adjacent to regions of nuclear loss show a range of defects, including spindles attached by only one pole and partially "collapsed" spindles.
Slightly misshapen Apc2ΔS egg chambers are often seen, with irregularities in their nurse cell arrays, particularly at the anterior ends. These ends appear somewhat elongated and occasionally squashed. Occasionally a slightly misplaced oocyte is seen.
At the permissive temperature (18oC) mutants are viable and fertile. At the restrictive temperature (25oC), homozygous embryos derived from heterozygous mothers are viable and heterozygous embryos derived from homozygous mutant mothers are wild-type and survive to adulthood. Homozygous embryos derived from homozygous females have severe abnormalities in their embryonic body plan; the denticle belts are replaced with an almost uniform expanse of naked cuticle. Many more cells on the dorsal surface of the embryo secrete fine hairs than wild type. Temperature shift experiments indicate that Apc2 activity is required between 4-10 hours after egg laying. Embryos shifted to the restrictive temperature after 10 hours develop into apparently normal adults, suggesting that Apc2 may be dispensible for adult patterning. Embryos that are both maternally and zygotically hemizygous are indistinguishable from embryos that are both maternally and zygotically homozygous.
Apc2ΔS, ApcQ8 has lethal | larval stage phenotype
Apc2ΔS, ApcQ8 has decreased occurrence of cell division | larval stage phenotype
Apc2ΔS, ApcQ8 has lethal | recessive | larval stage phenotype
Apc2ΔS is a suppressor of embryonic/first instar larval cuticle phenotype of wgl-17
Apc2ΔS, ApcQ8 has neuroblast | larval stage phenotype
Apc2ΔS, ApcQ8 double homozygotes die as second instar larvae. Double mutant second larval instar brains are essentially normal in size and the optic anlage has become epithelial. Second instar larval mushroom body neuroblasts proliferate as normal, but the number of other mitotic neuroblasts is drastically reduced relative to wild type. BrdU incorporation in the brain is drastically reduced in second instar larvae, with most labelled cells appearing to be mushroom body neuroblasts. The remaining larval neuroblasts retain the ability to divide asymetrically. The axonal scaffold is unaltered in Apc2ΔS, ApcQ8 double mutant embryos.
Apc2ΔS ApcQ8 double zygotic mutants are embryonic viable and exhibit a wild-type cuticle pattern, but die as larvae. In the embryonic progeny of Apc2ΔS ApcQ8/Apc2ΔS males and females crossed to each other, ventral cells secrete only naked cuticle. This is a more severe cuticle phenotype than that seen in Apc2ΔS maternal and zygotic mutant embryos.
Partially rescues the wgl-17 lawn of uniform denticles phenotype; the normal diversity of cuticular pattern elements and small expanses of naked cuticle are restored. The dsh75 mutant phenotype (embryos both maternally and zygotically homozygous for dsh75) is not affected if the embryos are also maternally and zygotically homozygous for Apc2ΔS. The arm8 mutant phenotype is not affected if the embryos are also maternally and zygotically homozygous for Apc2ΔS. The pan3 mutant phenotype is not affected if the embryos are also maternally and zygotically homozygous for Apc2ΔS.
Apc2ΔS is a less severe allele than Apc2d40.
Apc2 alleles can be divided into three categories based on their embryonic cuticle phenotypes, from weak to moderate to strong: Apc2e90 = Apc2b5 = Apc2N175K < Apc2c9 = Apc2ΔS = Apc2d40 < Apc2g41 = Apc2f90 = Apc2g10.