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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
Along with the implantation process, changes occur in the embryoblast to produce a bilaminar embryonic disc, composed of the epiblast and the hypoblast. Early in the 2nd week, the amniotic cavity appears as a space lined with amnioblasts derived from the epiblast. By the end of the 2nd week, the embryonic disc becomes oval in shape. Along the median line in the posterior region of the embryonic disc, a thickening of the epiblast called the primitive streak appears, and it defines the longitudinal axis of the embryo. During the 3rd week, lateral epiblast cells migrate medially, enter the primitive streak, and then converge to form the primitive groove.
Next Generation Tissue Engineering Strategies by Combination of Organoid Formation and 3D Bioprinting
Published in Naznin Sultana, Sanchita Bandyopadhyay-Ghosh, Chin Fhong Soon, Tissue Engineering Strategies for Organ Regeneration, 2020
Shikha Chawla, Juhi Chakraborty, Sourabh Ghosh
Another significant event during embryogenesis is gastrulation that involves patterning of pluripotent epiblast into the three germ layers that later develops into the embryo. This event involves a signaling pathway involving the BMP, Wnt and Nodal pathways (Chhabra et al. 2018). Thus, replication of such events seems quintessential to the approach of developmental biology inspired tissue engineering strategies (Fig. 4.2). This section would be incomplete without the mention of another interesting phenomenon of developmental biology, that is, directed tissue assembly, a process where closely placed tissue spheroids undergo fusion to replicate this fundamental biophysical and biological principle of directed tissue assembly (Mironov et al. 2009). Tissue engineers tried to take cues from this process and incorporated those features with 3D bioprinting, that led to the emergence of the new field of organ printing that holds promise to design and fabricate engineered tissue/mini organs for repair, regeneration and replacement of injured or damaged organs. One of our studies represents a true example of such an approach, where we first developed 3D spheroids of MSCs and chondrocytes for successful replication of mesenchymal condensation involving cell-cell adhesion formation through neural cell adhesion molecule (NCAM). These spheroids probably provided in vivo like microenvironment for development of stable cartilage tissue equivalent. Then these spheroids were combined with silk-gelatin hydrogel to develop 3D bioprinted cartilage tissue equivalents (Chameettachal et al. 2016) (Fig 4.3).
Current developments in human stem cell research and clinical translation
Published in Christine Hauskeller, Arne Manzeschke, Anja Pichl, The Matrix of Stem Cell Research, 2019
Stephanie Sontag, Martin Zenke
After the implantation of the blastocyst on days 7–9 the ICM develops into the epiblast (De Paepe et al., 2014). Epiblast stem cells are still pluripotent but as they have undergone more developmental stages they are referred to as primed pluripotent stem cells to distinguish them from naïve pluripotent stem cells of the pre-implantation ICM (Boroviak and Nichols, 2014). Epiblast stem cells lose their pluripotency when a thickened structure, called the primitive streak, is formed along the midline of the epiblast, which at this stage defines the body axes and orientations of the future embryo: cranial (head) versus caudal (feet), anterior (front) versus posterior (back), as well as left versus right end. During this process (known as gastrulation) the single-layered epiblast is reorganized into a three-layered gastrula forming the three germ layers: ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer).
Developing a Reflexive, Anticipatory, and Deliberative Approach to Unanticipated Discoveries: Ethical Lessons from iBlastoids
Published in The American Journal of Bioethics, 2022
Rachel A. Ankeny, Megan J. Munsie, Joan Leach
During the research process, the intermediate state of the cells was analyzed, and different types of cells were observed: some had gene expression patterns similar to epiblast (the type that eventually become fetal cells), which was expected since iPSC represent that cellular state. However, the research team also observed cells with patterns similar to trophectoderm, the layer of cells surrounding the blastocyst that supply the embryo with nourishment and which later form the major part of the placenta (these findings were originally published in Liu et al. 2020). Further interrogation of those intermediate states revealed that some of those cells undergoing reprogramming also expressed genes of the primitive endoderm (yolk sac). Given this finding, the researchers decided to place the cells undergoing reprogramming into a 3-D culture system to see how they would behave and interact in order to better characterize the cells. They found that after 6 days, cells self-assembled into aggregates; to their surprise, around 10% of these cellular clusters had a cavity reminiscent of that observed in a blastocyst, which prompted them to further characterize these structures. After a comprehensive molecular and functional analysis, the researchers concluded that they had generated what appeared to be blastocyst-like structures that they termed “iBlastoids” (short for “induced blastoids”). A critical point here is that these structures were derived from reprogramming adult human skin cells rather than being generated from existing pluripotent stem cells.
Pluripotency inducing Yamanaka factors: role in stemness and chemoresistance of liver cancer
Published in Expert Review of Anticancer Therapy, 2021
Homa Fatma, Hifzur Rahman Siddique
Moreover, it was reported that autophagy is one of the prominent regulators of gastric CSCs chemoresistance. A significant increase in autophagic markers has been found in CD44+ CD54+ gastric CSCs. Also, it was observed that NOTCH signaling is frequently deregulated in various cancers. NOTCH is said to be involved in autophagy-mediated breast CSCs chemoresistance [3]. It has been reported that EMT is induced by the activation of TGF-β, NOTCH, WNT, and Integrin, which downregulate E-Cadherin in CSCs. Furthermore, epigenetic silencing of SNAIL1, SLUG, ZEB also contribute to the molecular profile of EMT-induced CSCs. SNAIL1 and SLUG bind to the promoter region of E-Cadherin and facilitates EMT transition [23]. Moreover, NANOG is also considered a driving factor for the pluripotent state of epiblast as well as CSCs. NANOG/OCT4 signaling axis can induce stem cell-like behavior in cancer cells and stimulate EMT, self-renewal, and metastasis [24]. OSKM, GLI Family Zinc Finger (GLI1), Sal–like protein 4 (SALL4), and signal transducer and activator of transcription 3 (STAT3) are implicated in the induction of stemness in gastrointestinal cancer and colorectal cancer [25]. A diverse mechanism is associated with CSCs and chemoresistance. Understanding these mechanisms can help in enhancing the effect of chemotherapy.
Application of amniotic membrane in reconstructive urology; the promising biomaterial worth further investigation
Published in Expert Opinion on Biological Therapy, 2019
Jan Adamowicz, Shane Van Breda, Dominik Tyloch, Marta Pokrywczynska, Tomasz Drewa
The mammalian embryo is enclosed in the fluid filed amniotic sac of the placenta, surrounded by the AM. In humans, 6–7 days after fertilization, AM starts to develop during blastocyst implantation in the endometrium [6]. Subsequently, the embryoblast (inner cell mass within the blastocyst) differentiates into a bilaminar disc composed of the hypoblast and epiblast. Eventually, amnioblasts derived from the epiblast invade the space between the trophoblast and the embryonic disc, migrating to the inner amniotic layer and gradually constitute the external lining of the amniotic cavity. The amniotic and chorionic fetal membranes separate the embryo from the endometrium. The amniochorionic membrane forms the outer limits of the sac that encloses the embryo, while the innermost layer of the sac is the AM [7].