Dynamics of trophoblast differentiation in peri-implantation-stage human embryos.

Single-cell RNA sequencing of cells from cultured human blastocysts has enabled us to define the transcriptomic landscape of placental trophoblast (TB) that surrounds the epiblast and associated embryonic tissues during the enigmatic day 8 (D8) to D12 peri-implantation period before the villous placenta forms. We analyzed the transcriptomes of 3 early placental cell types, cytoTB (CTB), syncytioTB (STB), and migratoryTB (MTB), picked manually from cultured embryos dissociated with trypsin and were able to follow sublineages that emerged from proliferating CTB at the periphery of the conceptus. A unique form of CTB with some features of STB was detectable at D8, while mature STB was at its zenith at D10. A form of MTB with a mixed MTB/CTB phenotype arose around D10. By D12, STB generation was in decline, CTB had entered a new phase of proliferation, and mature MTB cells had begun to move from the main body of the conceptus. Notably, the MTB transcriptome at D12 indicated enrichment of transcripts associated with IFN signaling, migration, and invasion and up-regulation of HLA-C, HLA-E, and HLA-G. The STB, which is distinct from the STB of later villous STB, had a phenotype consistent with intense protein export and placental hormone production, as well as migration and invasion. The studies show that TB associated with human embryos is in rapid developmental flux during peri-implantation period when it must invade, signal robustly to the mother to ensure that the pregnancy continues, and make first contact with the maternal immune system.

Absence of SARS-CoV-2 (COVID-19 virus) within the IVF laboratory using strict patient screening and safety criteria.

RESEARCH QUESTION: Is there a risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral exposure and potential cross-contamination from follicular fluid, culture media and vitrification solution within the IVF laboratory using strict patient screening and safety measures? DESIGN: This was a prospective clinical study. All women undergoing transvaginal oocyte retrieval were required to have a negative SARS-CoV-2 RNA test 3-5 days prior to the procedure. Male partners were not tested. All cases used intracytoplasmic sperm injection (ICSI). The first tube of follicular fluid aspirated during oocyte retrieval, drops of media following removal of the embryos on day 5, and vitrification solution after blastocyst cryopreservation were analysed for SARS-CoV-2 RNA. RESULTS: In total, medium from 61 patients, vitrification solution from 200 patients and follicular fluid from 300 patients was analysed. All samples were negative for SARS-CoV-2 viral RNA. CONCLUSIONS: With stringent safety protocols in place, including testing of women and symptom-based screening of men, the presence of SARS-CoV-2 RNA was not detected in follicular fluid, medium or vitrification solution. This work demonstrates the possibility of implementing a rapid laboratory screening assay for SARS-CoV-2 and has implications for safe laboratory operations, including cryostorage recommendations.

Single Cell Collection of Trophoblast Cells in Peri-implantation Stage Human Embryos.

Human implantation, the apposition and adhesion to the uterine surface epithelia and subsequent invasion of the blastocyst into the maternal decidua, is a critical yet enigmatic biological event that has been historically difficult to study due to technical and ethical limitations. Implantation is initiated by the development of the trophectoderm to early trophoblast and subsequent differentiation into distinct trophoblast sublineages. Aberrant early trophoblast differentiation may lead to implantation failure, placental pathologies, fetal abnormalities, and miscarriage. Recently, methods have been developed to allow human embryos to grow until day 13 post-fertilization in vitro in the absence of maternal tissues, a time-period that encompasses the implantation period in humans. This has given researchers the opportunity to investigate human implantation and recapitulate the dynamics of trophoblast differentiation during this critical period without confounding maternal influences and avoiding inherent obstacles to study early embryo differentiation events in vivo. To characterize different trophoblast sublineages during implantation, we have adopted existing two-dimensional (2D) extended culture methods and developed a procedure to enzymatically digest and isolate different types of trophoblast cells for downstream assays. Embryos cultured in 2D conditions have a relatively flattened morphology and may be suboptimal in modeling in vivo three-dimensional (3D) embryonic architectures. However, trophoblast differentiation seems to be less affected as demonstrated by anticipated morphology and gene expression changes over the course of extended culture. Different trophoblast sublineages, including cytotrophoblast, syncytiotrophoblast and migratory trophoblast can be separated by size, location, and temporal emergence, and used for further characterization or experimentation. Investigation of these early trophoblast cells may be instrumental in understanding human implantation, treating common placental pathologies, and mitigating the incidence of pregnancy loss.