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Is the Human Embryo an Organism?
Published in Nicholas Colgrove, Bruce P. Blackshaw, Daniel Rodger, Agency, Pregnancy and Persons, 2023
Early human development is summarized in Figure 1.1. Briefly, upon sperm-egg fusion at fertilization, a single cell (the zygote) is formed (Figure 1.1A). The zygote divides rapidly, producing a number of smaller cells known as blastomeres (Figure 1.1B). By the second or third day following sperm-egg fusion, the blastomeres have formed a ball-like structure known as a morula-stage embryo (Figure 1.1C). Cell division continues, and by the fifth day, the embryo has grown to about one hundred cells and formed a fluid-filled structure known as a blastocyst (Figure 1.1E). At this stage, the first two committed cell types have arisen. The cells that make up the outer layer of the blastocyst are known as trophectoderm (TE). Inside the blastocyst is a cluster of cells, known as the inner cell mass (ICM).
Preimplantation Genetic Testing of Aneuploidies (PGT-A)
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Daniela N. Bakalova, Darren K. Griffin, Maria E. Póo, Alan R. Thornhill
Some groups and two RCTs have demonstrated positive results following good laboratory practice, including improved live-birth rates as compared to untested day 5 blastocysts [36]. However, as summarized in a meta-analysis comparing IVF with and without PGT-A using blastomere biopsies, data from several groups concluded no overall benefit of PGT-A on live-birth rates [37]. It should be noted that the studies of the meta-analysis employed an outdated FISH methodology, as compared to a more comprehensive aCGH approach used in one of the RCT studies. Again, this supports the theory that the success of blastomere biopsies is governed by good lab techniques.
Fertilization and normal embryonic and early fetal development
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Asim Kurjak, Ritsuko K. Pooh, Aida Salihagic-Kadic, Iva Lausin, Lara Spalldi-Barisic
A series of mitotic divisions lead to the development of the pre-embryo. The newly divided cells are called blastomeres. 24 hours after fertilization from single-cell zygote two-celled embryo is developed. 2 days after the fertilization embryo consists of 6 to 8 blastomeres. Blastomeres form cellular aggregates of distinct, totipotent, undifferentiated cells that retain the capacity to develop independently into normal pre-embryos. After every division, blastomeres become half of their previous size keeping the total size the same as in the beginning when it was just one cell. All up to eight-cell phase, blastomeres are cluster of cells inside the zona pellucida. But after the third division, they lose their round shape and they impact one to the other making compact round cluster of cells that are tightly connected by tight junctions. With that change, which is called compaction, cells from the outside start to differentiate from those inside. Third day after the fertilization, cells of the compact embryo divide again and morula arises. It contains 16 cells, outer part from which trophoblast will appear and inner cells from which embryo will appear.
Mitochondrial DNA copy number in cumulus granulosa cells as a predictor for embryo morphokinetics and chromosome status
Published in Systems Biology in Reproductive Medicine, 2023
Pitra Rahmawati, Budi Wiweko, Arief Boediono
In this study, no significant relationship was indicated between mtDNA copy number in CGCs and the morphokinetic parameters (tPN, tPNf, M1, M2, M3, CC1, CC2, CC3, S2, S3, DC, RC and MN). A considerable correlation was only observed with M1 after adjusting for the potential confounding factors. M1 constitutes the early stages of embryo development between t8 and t2. Prior to EGA which occurs at the 8-cell stage in humans (Conti and Franciosi 2018), degradation of maternal mRNA takes place hence the quality of early oocyte becomes the main factor for fertilization and early embryonic development potential (Miao et al. 2009; Van Blerkom 2011). Upon fertilization, mtDNA replication of a mammalian embryo is deferred until it reaches the morula stage (Thundathil et al. 2005). At the early cleavage stage, the embryos exhibit little to no expression of mtDNA replication factor (May-Panloup P et al. 2005; Thundathil et al. 2005; Spikings et al. 2007). As a result, the mtDNA copy number per blastomere decreases after every embryonic cell division. Consequently, the mtDNA copy number per blastomere decreases after every embryonic cell division and each blastomere capability to produce ATP through oxidative phosphorylation would therefore be reduced, increasing its dependence on anaerobic respiration for energy (Van Blerkom 2004). Should this occur during the early embryonic development, fragmentation of the blastomere could ensue, resulting in an embryo developmental arrest or retention and/or poor-quality blastocyst with a very small number of cells (May-Panloup et al. 2007).
Modification of late human embryo development after blastomere removal on day 3 for preimplantation genetic testing
Published in Systems Biology in Reproductive Medicine, 2021
Jenna Lammers, Arnaud Reignier, Sophie Loubersac, Sana Chtourou, Tiphaine Lefebvre, Paul Barrière, Thomas Fréour
Since the release of the first commercial time-lapse monitoring (TLM) system in 2009, several laboratories around the world have implemented this technology in order to improve embryo culture conditions and embryo quality evaluation. As it allows continuous monitoring of embryo development, this technology is a useful tool to observe embryo development after blastomere biopsy. The studies of Kirkegaard et al. 2012 and Bar-El et al. 2016, reported the use of TLM system to evaluate post-biopsy embryo development in PGT cycles. Both found that embryonic development was significantly delayed after blastomere biopsy on day 3, as compared to non-biopsied embryos. However, these studies were conducted in relatively limited population (109 and 751, respectively), thus highlighting the need for confirmation in larger studies. Therefore, this study aimed at evaluating the potential impact of blastomere biopsy on subsequent embryo development by comparing late morphokinetic parameters in embryos with or without blastomere biopsy on day 3.
Genetic analysis of embryo in a human case of spontaneous oocyte activation: a case report
Published in Gynecological Endocrinology, 2020
Yuanyuan Ye, Na Li, Xiaohong Yan, Rongfeng Wu, Weidong Zhou, Ling Cheng, Youzhu Li
Finally, there were 3 MII oocytes retrieved. Considering the results of the semen showed the total number of motile sperm did not meet the criteria to perform IVF in our laboratory (more than 2 × 105), therefore, ICSI was performed. However, prior to conducting ICSI, we surprisingly found that one of the MII oocytes presented 1 PN without injection. The abnormal oocyte did not be injected later and it kept the same in the next morning (D1). In the afternoon, it developed into an 8-cell embryo with almost 30% fragment 30 h after oocyte retrieval (Figure 1). Then blastomere biopsy was performed on the embryo by laser (Hamilton Thorne, Beverly, MA, USA). Blastomere was aspirated one by one from the embryo and released into the medium. Each intact blastomere was submitted to genome amplification (YK001B, Yikon, China). The results of DNA quantification implied there was only one cell containing DNA (Figure 2). The DNA containing cell was subjected to copy number variation (CNV) analysis and next generation sequencing (NGS) (Illumina, San Diego, CA, USA). The CNV results indicated a genotype of 48, XX, +17, +17 (Figure 3). The NGS data was used for MultiSNPs analysis and the results showed the SNPs of the biopsied embryo were exclusively in consistence with that of maternal side (see Supplementary material 1).