Aneuploid Human Oocytes and Embryos Possess Significantly Reduced Quantities of Telomere DNA.

Abstract

Aneuploidy represents the most prevalent form of genetic instability found in human embryos and is the leading cause of miscarriage and developmental delay in newborns. Although maternal age is a well known risk factor, the underlying molecular etiology of human aneuploidy is unknown. Since telomere DNA content is associated with genomic instability and is naturally reset during mammalian preimplantation embryonic development, telomere DNA quantity may play a role in the development of aneuploidy commonly found in human embryos. To begin to characterize the potential association of telomere biology with development of human aneuploidy, we have characterized relative telomere DNA quantity at various stages of human preimplantation embryogenesis. First, we developed a method capable of accurate quantitation of telomere DNA from single cells. Whole genome amplification (WGA) of picogram amounts of DNA from cells with previously established telomere DNA quantities provided results equivalent to those obtained using large quantities of purified total DNA (Pearson correlation coefficient=0.97). This technology was then applied to human oocytes and embryos. Excess WGA DNA was available for telomere DNA analysis of oocyte and embryo biopsies as a result of previously performing SNP microarray based 24 chromosome aneuploidy screening on human in vitro fertilization derived samples. Paired analysis of aneuploid and euploid polar bodies and embryonic cells from within the same patients' oocytes and embryos and within the same treatment cycle provided the greatest control over critical variables including maternal age. Embryo fragmentation rates, which were previously shown to correlate with telomere DNA length, weren't significantly different among aneuploid (9.2%) and euploid (9.7%) samples (P=0.75). Results demonstrated, for the first time, that aneuploid human polar bodies possess significantly less telomere DNA than euploid polar bodies (-3.07 fold, P=0.016). Since the first and second polar bodies are extruded upon completion of meiosis I and II, respectively, and reflect the chromosomal complement of the remaining oocyte, abnormalities observed in polar bodies are indicative of development of aneuploidy during meiosis of the oocyte. Therefore, the present results indicate that oocytes with reduced telomere DNA quantity are prone to development of aneuploidy during meiosis. We also show that aneuploid embryonic cells possess significantly less telomere DNA than euploid embryonic cells at the cleavage stage (-2.60 fold, P=0.002) but not at the blastocyst stage (-1.18 fold, P=0.340). These results indicate that reduced telomere length is associated with aneuploidy prior to embryonic genome activation between the cleavage and blastocyst stages of development. This further suggests that aneuploidy is not associated with failed resetting of telomere DNA length but is instead associated with failed telomere maintenance in the maternal genome during oogenesis and early embryo development. (platform)