These zygotes had likely arrested at the spindle assembly checkpoint of the first cell cycle [ 24].
Following the first round of centriole duplication in the zygote, the two centrosomes, now each with a pair of centrioles, direct assembly of a bipolar spindle during the first mitotic division.
The midbody, a cytoplasmic structure formed by the compression of the microtubule spindle during the first embryonic cleavage, was proposed to be involved in the positioning of spermatozoon mitochondria in the region that eventually gives rise to germ cells [ 12].
According to Rienzi et al. (2003) high degrees of misalignment between the meiotic spindle and the first PB increased risk of fertilization abnormalities.
In zygotes lacking MBK-2, MEI-1 degradation is delayed and MEI-1 activity interferes with the formation of the mitotic spindle, causing the first cleavage to fail.
(A ) Schematic and fluorescence confocal images of the spindle at early anaphase of the first mitotic division in C. elegans embryos from the indicated genotypes.
Overall, our observations show that during anastral spindle formation, the first MTs appeared in the vicinity of the condensing chromosomes.
Given the aberrant behavior of mitotic spindles in the first three cleavages prior to LR symmetry breaking (Bergmann et al., 2003), the it143 mutant could have slightly misplaced neighbors that could as well result in impaired LR symmetry breaking.
In purely diploid organisms, the sperm, in addition to contributing half of the hereditary material, provides a centrosome derived from the sperm tail basal body that is essential for organizing the first mitotic spindle of the embryo (Schatten 1994).
This is followed by segregation of homologues and non-sister chromatids by unipolar attachment of sister kinetochores to spindles, during the first meiotic division.
