The human embryonic genome is karyotypically complex, with chromosomally abnormal cells preferentially located away from the developing fetus

AbstractSTUDY QUESTIONAre chromosome abnormalities detected at Day 3 post-fertilization predominantly retained in structures of the blastocyst other than the inner cell mass (ICM), where chromosomally normal cells are preferentially retained?SUMMARY ANSWERIn human embryos, aneuploid cells are sequestered away from the ICM, partly to the trophectoderm (TE) but more significantly to the blastocoel fluid within the blastocoel cavity (Bc) and to peripheral cells (PCs) surrounding the blastocyst during Day 3 to Day 5 progression.WHAT IS KNOWN ALREADYA commonly held dogma in all diploid eukaryotes is that two gametes, each with ‘n’ chromosomes (23 in humans), fuse to form a ‘2n’ zygote (46 in humans); a state that remains in perpetuity for all somatic cell divisions. Human embryos, however, display high levels of chromosomal aneuploidy in early stages that reportedly declines from Day 3 (cleavage stage) to Day 5 (b lastocyst) post-fertilization. While this observation may be partly because of aneuploid embryonic arrest before blastulation, it could also be due to embryo ‘normalization’ to a euploid state during blastulation. If and how this normalization occurs requires further investigation.STUDY DESIGN, SIZE, DURATIONA total of 964 cleavage-stage (Day 3) embryos underwent single-cell biopsy and diagnosis for chromosome constitution. All were maintained in culture, assessing blastulation rate, both for those assessed euploid and aneuploid. Pregnancy rate was assessed f...
Source: Human Reproduction - Category: Reproduction Medicine Source Type: research