Cellular fragmentation-­mediated chromosome elimination and blastomere exclusion: mechanisms for overcoming chromosome missegregation in the rhesus macaque preimplantation embryo. Public Deposited

In this dissertation, the rhesus macaque embryo was evaluated for aneuploidy frequency to determine if it is a suitable translation model to study human embryology. Using single-­cell DNA-­Sequencing, chromosome instability was established in the rhesus macaque monkey model and found to occur in 74% of embryos at a nearly identical rate to human embryos. Additional findings of reciprocal sub-­chromosomal deletions and duplications support  previous  reports  that  chromosome  breakage  is  common  in  human  embryos.  Pairing sequencing technology with non-­invasive live-­cell time-­lapse imaging revealed that multipolar divisions were present as well and often resulted in chaotic aneuploidy, which is defined as greater than five whole or segmental chromosomes affected in at least one blastomere where chromosome distribution amongst cells appeared unconstrained and random [1]. Furthermore, measuring cell cycle division intervals to the four-­cell stage, was predictive of whether an embryo would reach the blastocyst stage or arrest. When the  cellular  fragments  of  embryos  were  also  sequenced,  ~20%  of  rhesus  macaque  embryos contain cellular fragments that encapsulate whole or partial chromosomes, either maternal  or  paternal  origin.  Confocal  microscopy  revealed  that  indeed,  micronuclei  containing missegregated chromosomes are found within the cellular fragments of cleavage stage embryos. These ejected micronuclei experienced extensive DNA damage which may indicate their expulsion for this reason. Despite frequent chromosomal errors, rhesus macaque embryos were also found that prevented cellular fragments and non-­dividing blastomeres from incorporating at the blastocyst stage.

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