SAC during early cell divisions: Sacrificing fidelity over timely division, regulated differently across organisms Chromosome alignment and segregation are left unsupervised from the onset of development until checkpoint activity is acquired, varying from species to species

摘要

Early embryogenesis is marked by a frail Spindle Assembly Checkpoint (SAC). The time of SAC acquisition varies depending on the species, cell size or a yet to be uncovered developmental timer. This means that for a specific number of divisions, biorientation of sister chromatids occurs unsupervised. When error-prone segregation is an issue, an aneuploidy-selective apoptosis system can come into play to eliminate chromosomally unbalanced cells resulting in healthy newborns. However, aneuploidy content can be too great to overcome, endangering viability.