A PGD pregnancy achieved by embryo copy number variation sequencing with confirmation by non-invasive prenatal diagnosis

Clinical application of next-generation sequencing in preimplantation genetic diagnosis cycles for Robertsonian and reciprocal translocations

PURPOSE

The purpose of this study was to apply next-generation sequencing (NGS) technology to identify chromosomally normal embryos for transfer in preimplantation genetic diagnosis (PGD) cycles for translocations.

METHODS

A total of 21 translocation couples with a history of infertility and repeated miscarriage presented at our PGD clinic for 24-chromosome embryo testing using copy number variation sequencing (CNV-Seq).

RESULTS

Testing of 98 embryo samples identified 68 aneuploid (69.4 %) and 30 (30.6 %) euploid embryos. Among the aneuploid embryos, the most common abnormalities were segmental translocation imbalances, followed by whole autosomal trisomies and monosomies, segmental imbalances of non-translocation chromosomes, and mosaicism. In all unbalanced embryos resulting from reciprocal translocations, CNV-Seq precisely identified both segmental imbalances, extending from the predicted breakpoints to the chromosome termini. From the 21 PGD cycles, eight patients had all abnormal embryos and 13 patients had at least one normal/balanced and euploid embryo available for transfer. In nine intrauterine transfer cycles, seven healthy babies have been born. In four of the seven children tested at 18 weeks gestation, the karyotypes matched with the original PGD results.

CONCLUSION

In clinical PGD translocation cycles, CNV-Seq displayed the hallmarks of a comprehensive diagnostic technology for high-resolution 24-chromosome testing of embryos, capable of identifying true euploid embryos for transfer.

Casein kinase 1 (α, δ and ε) localize at the spindle poles, but may not be essential for mammalian oocyte meiotic progression

CK1 (casein kinase 1) is a family of serine/threonine protein kinase that is ubiquitously expressed in eukaryotic organism. CK1 members are involved in the regulation of many cellular processes. Particularly, CK1 was reported to phosphorylate Rec8 subunits of cohesin complex and regulate chromosome segregation in meiosis in budding yeast and fission yeast. (1-3) Here we investigated the expression, subcellular localization and potential functions of CK1α, CK1δ and CK1ε during mouse oocyte meiotic maturation. We found that CK1α, CK1δ and CK1ε all concentrated at the spindle poles and co-localized with γ-tubulin in oocytes at both metaphase I (MI) and metaphase II (MII) stages. However, depletion of CK1 by RNAi or overexpression of wild type or kinase-dead CK1 showed no effects on either spindle organization or chromosome segregation during oocyte meiotic maturation. Thus, CK1 is not the kinase that phosphorylates Rec8 cohesin in mammalian oocytes, and CK1 may not be essential for spindle organization and meiotic progression although they localize at spindle poles.

Detection and quantitation of chromosomal mosaicism in human blastocysts using copy number variation sequencing

OBJECTIVE

Currently, our understanding of the nature and reproductive potential of blastocysts associated with trophectoderm (TE) lineage chromosomal mosaicism is limited. The objective of this study was to first validate copy number variation sequencing (CNV-Seq) for measuring the level of mosaicism and second, examine the nature and level of mosaicism in TE biopsies of patient's blastocysts.

METHOD

TE biopy samples were analysed by array comparative genomic hybridization (CGH) and CNV-Seq to discriminate between euploid, aneuploid and mosaic blastocysts.

RESULTS

Using artificial models of TE mosaicism for five different chromosomes, CNV-Seq accurately and reproducibly quantitated mosaicism at levels of 50% and 20%. In a comparative 24-chromosome study of 49 blastocysts by array CGH and CNV-Seq, 43 blastocysts (87.8%) had a concordant diagnosis and 6 blastocysts (12.2%) were discordant. The discordance was attributed to low to medium levels of chromosomal mosaicism (30-70%) not detected by array CGH. In an expanded study of 399 blastocysts using CNV-Seq as the sole diagnostic method, the proportion of diploid-aneuploid mosaics (34, 8.5%) was significantly higher than aneuploid mosaics (18, 4.5%) (p < 0.02).

CONCLUSION

Mosaicism is a significant chromosomal abnormality associated with the TE lineage of human blastocysts that can be reliably and accurately detected by CNV-Seq.

Nuf2 is required for chromosome segregation during mouse oocyte meiotic maturation

Nuf2 plays an important role in kinetochore-microtubule attachment and thus is involved in regulation of the spindle assembly checkpoint in mitosis. In this study, we examined the localization and function of Nuf2 during mouse oocyte meiotic maturation. Myc6-Nuf2 mRNA injection and immunofluorescent staining showed that Nuf2 localized to kinetochores from germinal vesicle breakdown to metaphase I stages, while it disappeared from the kinetochores at the anaphase I stage, but relocated to kinetochores at the MII stage. Overexpression of Nuf2 caused defective spindles, misaligned chromosomes, and activated spindle assembly checkpoint, and thus inhibited chromosome segregation and metaphase-anaphase transition in oocyte meiosis. Conversely, precocious polar body extrusion was observed in the presence of misaligned chromosomes and abnormal spindle formation in Nuf2 knock-down oocytes, causing aneuploidy. Our data suggest that Nuf2 is a critical regulator of meiotic cell cycle progression in mammalian oocytes.