IncenpQA26 oocytes exhibit only one focus for each pair of centromeres and mono-orientation of homologous chromosomes while they exhibit chromosome movements and bipolar spindles (in majority) as compared to controls.
55% of stage 12 and 13 oocytes show prometaphase I configurations with separated chromosomes in homozygous females, but by stage 14, the oocytes have configurations comparable to those seen in wild-type control oocytes.
Embryos derived from IncenpQA26 females arrest early, with defects such as chromosome bridging in the first anaphase.
The condensed chromosomes normally present in the polar body rosette structure of early embryos have aberrant morphology in embryos derived from IncenpQA26 females; the chromosomes are elongated and fragmented.
The morphology of the metaphase-I arrested spindle in female meiosis is disrupted in over 50% of oocytes in IncenpQA26 females. Typical defects include the formation of one or more ectopic spindle poles, usually around the equator or next to the main poles. Chromosome alignment or location is abnormal in 32% of mutant metaphase-I arrested oocytes, compared to 15% of control oocytes.
Live-imaging analysis of metaphase I-arrested spindles in IncenpQA26 oocytes indicates that approximately 40% have an abnormal morphology, typically ectopic or split poles, at the beginning of the observation. Half of these abnormal spindles become bipolar during the observation (typically 20-40 minutes), whereas some of the others change their morphology but remain abnormal. Conversely, most of the initially bipolar spindles remain bipolar during the observation, but some lose their bipolarity, mostly through the appearance of ectopic poles, or, less often, splitting of poles. Ectopic poles usually grow from the spindle equatorial region, and spindle bipolarity is restored by disassembling the ectopic pole or merging it with one of the main poles. In total, more than one-third of the observed spindles show at least one interconversion between bipolar and abnormal morphology during the period of observation.
Spindle microtubules are assembled around the chromosomes after nuclear envelope breakdown in the mutant oocytes and multiple transitory poles appear at the beginning of spindle formation, as occurs in wild type. However, unlike in wild type, even after one spindle axis has become dominant, other poles continue to be formed in the mutant oocytes. In addition, the time between nuclear envelope breakdown and the first appearance of microtubules around the chromosomes is significantly increased in the mutant oocytes compared to wild type.
The spindle equatorial region is defective in the mutant oocytes, having a significantly reduced tubulin intensity at the midzone relative to the poles compared to wild-type oocytes.
The length of the metaphase I spindle in mutant oocytes is not significantly different from that of wild type.
Homozygous female complete meiosis without detectable defects, but there are defects in embryonic mitoses.
Homozygous males have reduced fertility.
Mutant males show defects in meiosis I; small bits of chromatin that could result from chromosome fragmentation or aberrant condensation are seen.
Homozygous males show increased nondisjunction of the sex chromosomes during meiosis (15.8%) compared to controls (0.6%).
Mutant spermatocytes show defective chromosome condensation in meiosis; prophase I figures with loosely packed and minimally condensed chromosomes are seen in 34% of mutant spermatocytes compared to 14% of wild-type spermatocytes. The mutant spermatocytes also show premature loss of sister chromatid cohesion in prometaphase I; bivalents that are compacted into blobs but have protruding arms that appear to be single sister chromatids are seen. Anaphase I spermatocytes contain completely separated sister chromatids at the poles and prometaphase II cells with separated sister chromatids are also seen. Precocious sister chromatid separation is seen in 34% of mutant spermatocytes in which the chromosome arrangement allows cohesion to be assessed. Aneuploid meiosis II spermatocytes are also seen.
Eggs derived from homozygous females show no visible sign of embryonic development when observed under transmitted light in a stereo microscope. After 4-6 hours after egg deposition the originally unformly dense (like wild type) yolk mass starts to disintegrate into a network of darker and lighter yolk droplets. The defect may be in fertilisation or very early in embryonic development.