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.

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SUMMARYRecent advances in human blastoids generated from naïve pluripotent stem cells have opened a new avenue for modelling early human development and implantation. Despite the success, however, existing protocols have several limitations, e.g., the use of custom-built microwell arrays impedes wide adoption by the research community, and mass production of human blastoids is hampered by low-output or low-efficiency methods. To address these issues, here we developed an optimized protocol based on commercially available microwell plates, which enabled efficient generation of high-fidelity human blastoids at a large scale. Leveraging on the improved protocol, we identified MAPK. PI3K/AKT and mTOR signaling pathways were activated in both blastoids and blastocyst, and discovered endometrial stromal effects in promoting trophoblast cell survival, proliferation and syncytialization during extended co-culture with blastoids. Our optimized protocol will facilitate broader use of human blastoids as an accessible, perturbable, scalable, tractable, and ethical model for human blastocysts.

Research Question: In the early stages of the COVID-19 pandemic, IVF clinics stopped the majority of patient treatment cycles to minimize the risk of disease transmission. The risk of SARS-CoV-2 viral exposure and potential cross contamination within the IVF lab remains largely unclear. To that end, the objective of this study was to examine follicular fluid (FF), culture media (M) and vitrification solution (VS) for SARS-CoV-2 in an IVF lab. Design : Prospective clinical study. All females undergoing transvaginal oocyte retrieval (TVOR) were required to have a negative SARS-CoV-2 RNA test 3-4 days prior to the procedure. Male partners were not tested. All cases utilized intracytoplasmic sperm injection (ICSI). The first tube of FF aspirated during oocyte retrieval, M drops following removal of embryos on day 5, and VS after blastocyst cryopreservation were analyzed for SARS-CoV-2 RNA. Results: In total, M from 61 patients, VS from 200 patients, and FF from 300 patients were analyzed. All samples were negative for SARS-CoV-2 viral RNA. Conclusion(s): With stringent safety protocols in place, including female patient testing and symptom-based screening of men, the presence of SARS-CoV-2 RNA was not detected in FF, M or VS. 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.

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