The unknown human trophectoderm: implication for biopsy at the blastocyst stage
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COMMENTARY
The unknown human trophectoderm: implication for biopsy at the blastocyst stage Angelo Tocci 1 Received: 5 June 2020 / Accepted: 11 August 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Trophectoderm biopsy is increasingly performed for pre-implantation genetic testing of aneuploidies and considered a safe procedure on short-term clinical outcome, without strong assessment of long-term consequences. Poor biological information on human trophectoderm is available due to ethical restrictions. Therefore, most studies have been conducted in vitro (choriocarcinoma cell lines, embryonic and pluripotent stem cells) and on murine models that nevertheless poorly reflect the human counterpart. Polarization, compaction, and blastomere differentiation (e.g., the basis to ascertain trophectoderm origin) are poorly known in humans. In addition, the trophectoderm function is poorly known from a biological point of view, although a panoply of questionable and controversial microarray studies suggest that important genes overexpressed in trophectoderm are involved in pluripotency, metabolism, cell cycle, endocrine function, and implantation. The intercellular communication system between the trophectoderm cells and the inner cell mass, modulated by cell junctions and filopodia in the murine model, is obscure in humans. For the purpose of this paper, data mainly on primary cells from human and murine embryos has been reviewed. This review suggests that the trophectoderm origin and functions have been insufficiently ascertained in humans so far. Therefore, trophectoderm biopsy should be considered an experimental procedure to be undertaken only under approved rigorous experimental protocols in academic contexts. Keywords Trophectoderm biopsy . Polarization . Compaction . Cell junctions . Human embryo
Introduction The trophectoderm (TE) is the external cell mass of the blastocyst that develops into the placenta and the other extraembryonic membranes. For implantation to occur, the embryo needs to acquire a well-differentiated functional TE, whose aim is to interact with the endometrium, start implantation, and provide a proper placental development. Due to ethical restrictions, research on the human embryo is scant and conducted on very few embryos [1–3] sometimes obtained from in vitro matured oocytes [4, 5] which do not necessarily reflect the physiological counterpart. Studies on TE cells have been preferentially undertaken on animal embryos and in vitro models (choriocarcinoma cell lines, embryonic and pluripot e n t s t e m c e l l s ) a s t he y a r e m o r e av a i l a b l e an d
* Angelo Tocci [email protected] 1
Reproductive Medicine Unit, Gruppo Donnamed, Via Giuseppe Silla 12, Rome, Italy
morphologically similar to the human counterpart. Nevertheless, these models display marked differences in gene expression, epigenetic changes, chromatin remodeling, transcriptional activity, genome activation, timing of polarization and compaction, blastocyst formation, implantati
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