4.3% of late stage 13 oocytes show metaphase I arrest in twe1 females, while 84% of the mutant oocytes are still in prophase I at this stage (virtually all wild-type oocytes are in metaphase I at this stage). At stage 14, 83% of mutant oocytes have abnormal DNA morphology. 82% of the mutant oocytes fail to form or maintain the meiotic spindle at stage 14 and 18% have abnormal spindle masses with DNA attached.
The nuclear envelope persists for longer than normal in twe1 oocytes.
Stage 14 mutant oocytes are not dehydrated (in contrast to wild-type oocytes at this stage) and have abnormal yolk morphology.
96% of 0- to 3-hour embryos derived from homozygous females have dispersed or undetectable DNA. Of these, approximately half have abnormal spindles associated with DNA masses, whereas 8% have free spindle asters and/or thin, long spindles.
Homozygous females show delayed nuclear envelope breakdown in the oocyte; the nucleus is still present until early stage 14.
When heterozygous with tweZO758 meiotic entry occurs and the phenotype is similar to loss of function twe or bol alleles.
Primary spermatocytes entering the first meiotic division have bivalents with only partially condensed chromosomes. Chromosome segregation and cytokinesis fail to occur and meiotic spindles do not form in the spermatocytes. Meiotic arrest does not occur. Nucleolar breakdown occurs and the cells proceeds to the round spermatid stage, and mitochondrial aggregates form. Eventually the bivalents decondense and assume a thin crescent shape apposed to the nuclear membrane.
Meiotic spindles and metaphase plates are never formed at high temperatures. Chromosomes still condense in late spermatocytes and spermatid differentiation continues. Heat induced expression of stghs.PE3 restores spindle formation in testis.
Mutation prevents spindle formation during the entry into meiosis in males but chromosome condensation and nuclear envelope breakdown still occur. Testes contain disordered sperm heads on partially elongated sperm. Meiotic spindles do form in females but appear abnormal. Female meiotic divisions do not arrest at metaphase I as in wild type but continue repeatedly, leading to gross non-disjunction. Small chromatin masses often segregate properly to the spindle poles and persist into the embryos where they appear to participate in mitotic divisions on thin spindles. In addition the embryos contain a small number of large chromatin masses that are not associated with spindles.
Large proportion of eggs derived from homozygous twe1 mothers lack nuclear structures or have 5 enlarged 'nuclei' within them. The few reamining undergo a number of normal mitotic cycles. Meiosis does not occur in homozygous twe1 males.
Block of meiosis in males and severe meiotic defects in females.
Eggs derived from homozygous females initiate development and cytoplasmic clearing occurs in a narrow zone around the egg periphery (in wild-type embryos this process is coupled to the arrival of the nuclei at the periphery). This cytoplasmic clearing appears irregular. The eggs do not seem to develop beyond this stage; pole cells are not formed and cellularisation does not occur. However, about two hours after cytoplasmic clearing, the egg periphery starts to show local contractions, in what might be an attempt at gastrulation.