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Harmoush B, Tsikolia N, Viebahn C. Epiblast and trophoblast morphogenesis in the pre-gastrulation blastocyst of the pig. A light- and electron-microscopical study. J Morphol 2021; 282:1339-1361. [PMID: 34176156 DOI: 10.1002/jmor.21389] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 05/31/2021] [Accepted: 06/15/2021] [Indexed: 01/18/2023]
Abstract
The epiblast of the amniote embryo is of paramount importance during early development as it gives rise to all tissues of the embryo proper. In mammals, it emerges through segregation of the hypoblast from the inner cell mass and subsequently undergoes transformation into an epithelial sheet to create the embryonic disc. In rodents and man, the epiblast cell layer is covered by the polar trophoblast which forms the placenta. In mammalian model organisms (rabbit, pig, several non-human primates), however, the placenta is formed by mural trophoblast whereas the polar trophoblast disintegrates prior to gastrulation and thus exposes the epiblast to the microenvironment of the uterine cavity. Both, polar trophoblast disintegration and epiblast epithelialization, thus pose special cell-biological requirements but these are still rather ill-understood when compared to those of gastrulation morphogenesis. This study therefore applied high-resolution light and transmission electron microscopy and three-dimensional (3D) reconstruction to 8- to 10-days-old pig embryos and defines the following steps of epiblast transformation: (1) rosette formation in the center of the ball-shaped epiblast, (2) extracellular cavity formation in the rosette center, (3) epiblast segregation into two subpopulations - addressed here as dorsal and ventral epiblast - separated by a "pro-amniotic" cavity. Ventral epiblast cells form between them a special type of desmosomes with a characteristic dense felt of microfilaments and are destined to generate the definitive epiblast. The dorsal epiblast remains a mass of non-polarized cells and closely associates with the disintegrating polar trophoblast, which shows morphological features of both apoptosis and autophagocytosis. Morphogenesis of the definitive epiblast in the pig may thus exclude a large portion of bona fide epiblast cells from contributing to the embryo proper and establishes contact de novo with the mural trophoblast at the junction between the two newly defined epiblast cell populations.
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Affiliation(s)
- Braah Harmoush
- Institute of Anatomy and Embryology, University Medical Centre Göttingen, Göttingen, Germany
| | - Nikoloz Tsikolia
- Institute of Anatomy and Embryology, University Medical Centre Göttingen, Göttingen, Germany
| | - Christoph Viebahn
- Institute of Anatomy and Embryology, University Medical Centre Göttingen, Göttingen, Germany
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Bou G, Liu S, Sun M, Zhu J, Xue B, Guo J, Zhao Y, Qu B, Weng X, Wei Y, Lei L, Liu Z. CDX2 is essential for cell proliferation and polarity in porcine blastocysts. Development 2017; 144:1296-1306. [PMID: 28219949 DOI: 10.1242/dev.141085] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 02/03/2017] [Indexed: 01/18/2023]
Abstract
The role of CDX2 in trophectoderm (TE) cells has been extensively studied, yet the results are contradictory and species specific. Here, CDX2 expression and function were explored in early porcine embryos. Notably, siRNA-mediated gene knockdown and lentivirus-mediated TE-specific gene regulation demonstrated that CDX2 is essential for the maintenance of blastocyst integrity by regulating the BMP4-mediated blastocyst niche and classic protein kinase C (PKC)-mediated TE polarity in mammalian embryos. Mechanistically, CDX2-depleted porcine embryos stalled at the blastocyst stage and exhibited apoptosis and inactive cell proliferation, possibly resulting from BMP4 downregulation. Moreover, TE cells in CDX2-depleted blastocysts displayed defective F-actin apical organization associated with downregulation of PKCα (PRKCA). Collectively, these results provide further insight into the functional diversity of CDX2 in early mammalian embryos.
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Affiliation(s)
- Gerelchimeg Bou
- College of Life Science, Northeast Agricultural University, Harbin 150030, China.,College of Animal Science, Inner Mongolia Agricultural University, Huhhot 010018, China
| | - Shichao Liu
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Mingju Sun
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Jiang Zhu
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Binghua Xue
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Jia Guo
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Yueming Zhao
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Bo Qu
- Life Science and Biotechnique Research Center, Northeast Agricultural University, Harbin 150030, China
| | - Xiaogang Weng
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Yanchang Wei
- College of Life Science, Northeast Agricultural University, Harbin 150030, China
| | - Lei Lei
- Department of Histology and Embryology, Harbin Medical University, Harbin 150081, China
| | - Zhonghua Liu
- College of Life Science, Northeast Agricultural University, Harbin 150030, China .,Key Laboratory of Animal Genetics, Breeding and Reproduction, Education Department of Heilongjiang Province, Harbin 150030, China
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