I-38: Chromosome Instability in The Cleavage Stage Embryo

Recently, we demonstrated chromosome instability (CIN) in human cleavage stage embryogenesis following in vitro fertilization (IVF). CIN not necessarily undermines normal human development (i.e. when remaining normal diploid blastomeres develop the embryo proper), however it can spark a spectrum of conditions, including loss of conception, genetic disease and genetic variation development. To study embryonic CIN further we have developed new methods based on high-resolution microarray as well as next-generation sequencing technology that characterize the genome of a single human cell. We delivered proof-of-principle for detecting various types of structural variants, including Mb- to Kb-sized duplications and deletions, in single human (tumor) cells by low coverage sequencing and mapping. Based on the copy number changes that were detected by single-cell microarray analysis of multiple blastomeres of the same embryo, it was hypothesized that chromosome breakages and fusions occur frequently in human cleavage stage embryos and instigate subsequent breakage-fusion-bridge cycles. In addition, we hypothesized that the DNA breaks present in spermatozoa could trigger this CIN. To test these hypotheses, we genotyped both parents as well as 93 blastomeres from 24 IVF embryos and developed a novel SNP-array based algorithm to determine the parental origin of (aberrant) loci in single cells. Paternal as well as maternal alleles were commonly rearranged in the blastomeres indicating that sperm-specific DNA-breaks do not explain the majority of these structural variants. In addition, single-cell genome sequencing together with parent-oforigin SNP-array and microarray-guided FISH analyses demonstrate that breakage-fusion-bridge cycles as well as more complex rearrangements are sparked in the human cleavage stage embryo. Our data provide evidence that the human cleavage stage embryo is likely an important source of constitutional chromosomal disorders. The developed single-cell genome analysis methods are generic and will deliver novel insights in embryo and tumor genome research.