Embryos derived from grpunspecified females have significantly shorter interphases during cycles 11, 12 and 13 compared to wild-type or lokp6 single mutant embryos.
When exposed to increasing levels of X ray irradiation mutant animals exhibit similar levels of lethality to wild-type. However no decrease in mitotic index is seen in mutants, in contrast to wild-type, which show a gradual reduction of mitotic index with increasing X ray dose. Mutants also exhibit a slightly suppressed reduction of the frequency of anaphase seen when wild-type animals are exposed to increasing does ox X ray.
In embryos derived from homozygous females mated to wild-type males, microtubule organisation is indistinguishable from that of wild-type embryos through the first 11 divisions. During mitosis 12, the spindles are somewhat shorter than wild type and the centrosomal foci are somewhat weaker than normal, but microtubule organisation during interphase following mitosis 12 appear normal. During mitosis 13 the centrosomal foci become essentially undetectable and anastral spindles with broad poles are formed. The chromosomes do not form a compact mass at the metaphase plate. Mitosis 13 is prolonged. On exit from mitosis 13, centrosomal foci reappear and organise interphase microtubule arrays.
After interphase cycle 12, grp-derived embryos begin to exhibit an uneven nuclear distribution and irregular shaped nuclei. This phenotype becomes more extreme as the nuclei form distinct clusters. Cellularization does not occur. Abnormal nuclei do not recede into the interior. Fusion of sister nuclei occurs during telophase of nuclear cycle 12, and midbody formation is abnormal. Embryos arrest in cycle 13 with their chromosomes encompassed by spindles. Unusually, X irradiation induces metaphase arrest at all syncytial cycles.