Cellular and genetic analysis of oocytes and embryos in a human case of spontaneous oocyte activation

Abstract

Unusual and consistent defects in infertility patients merit attention as these may indicate an underlying genetic abnormality, in turn necessitating tailored management strategies. We describe a case of repeated early pregnancy loss from in vivo conceptions, followed by cancelled embryo transfers after one IVF and one ICSI/PGD cycle. Following the unexpected presence of cleaved embryos at the fertilization check in the first IVF attempt, oocytes and embryos were subsequently analyzed in an ICSI/PGD case. Part of the oocyte cohort was fixed at retrieval for a cellular evaluation of microtubules, microfilaments and chromatin. The remaining oocytes were injected with sperm, and resultant embryos were biopsied for genetic analysis by fluorescence in situ hybridization (FISH), single-nucleotide polymorphism (SNP) microarray for 23 chromosome pairs, as well as with PCR for sex chromosomes. The presence of interphase microtubule networks and pronuclear structures indicated that oocytes were spontaneously activated by the time of retrieval. FISH revealed aneuploidy in all seven blastomeres analyzed, with all but two lacking Y chromosomes. Microarray SNP analysis showed an exclusively maternal origin of all blastomeres analyzed, which was further confirmed by PCR. From our multi-faceted analyses, we conclude that spontaneous activation, or parthenogenesis, was probably the pathology underlying our patient's recurrent inability to maintain a normal pregnancy. Such analyses may prove beneficial not only in diagnosing case-specific aberrations for other patients with similar or related failures, but also for furthering our general understanding of oocyte activation.