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Introduction to Genomics
Published in Altuna Akalin, Computational Genomics with R, 2020
DNA methylation is also related to a key core and proximal promoter element: CpG islands. CpG islands are usually unmethylated, however, for some genes, CpG island methylation accompanies their silenced expression. For example, during X-chromosome inactivation, many CpG islands are heavily methylated and the associated genes are silenced. In addition, in embryonic stem cell differentiation, pluripotency-associated genes are silenced due to DNA methylation. Apart from methylation, there are other kinds of DNA modifications present in mammalian genomes, such as hydroxy-methylation and formylcytosine. These are other modifications under current research that are either intermediate or stable modifications with distinct functional associations. There are at least a dozen distinct DNA modifications observed when we look across all studied species (Sood et al., 2019).
Dentin-Pulp Complex Regeneration
Published in Vincenzo Guarino, Marco Antonio Alvarez-Pérez, Current Advances in Oral and Craniofacial Tissue Engineering, 2020
Amaury Pozos-Guillén, Héctor Flores
There are two types of stem cells: embryonic and postnatal. Embryonic stem cells are pluripotent cells capable of differentiating into any cell type as well as maintaining an undifferentiated state. These cells are plastic and have the capacity to develop into various specialized cell types with an enormous potential for tissue regeneration. Postnatal stem cells have been isolated from various tissues including bone marrow, neural tissue, dental pulp and periodontal ligament. These are multipotent stem cells capable of differentiating into more than one cell type, but not all cell types (Antoniou 2001).
Mosaicism Mechanisms in Preimplantation Embryos
Published in Darren K. Griffin, Gary L. Harton, Preimplantation Genetic Testing, 2020
Maurizio Poli, Antonio Capalbo
Early embryonic cells maintain pluripotency, thus being able to differentiate in all cell lineages. In vivo, following multiple rounds of cell division, embryonic cells enter irreversible pathways of differentiation, which will be maintained in subsequent divisions [12]. If the defective mitotic event occurs after a certain differentiation pathway is undertaken, only that cell lineage or part of that tissue will be affected (Figure 8.2). Lineage commitment of cells carrying secondary karyotypes has significant impact on the type of mosaicism affecting the embryo. For instance, when both main embryo cell lineages (e.g., ICM, TE) are composed of primary and secondary karyotypes (i.e., defective mitotic event occurring at a very early developmental stage), the embryo will show total mosaicism (Figure 8.3a). Alternatively, if the defective mitotic event occurs at the earliest stage of cell lineage commitment, the secondary karyotype will be equally represented in all cells composing the specific tissue and all the cells deriving from downstream differentiation processes (confined complete TE/ICM mosaicism) (Figure 8.3b, c). If the defective mitotic event occurs in a differentiated cell after several divisions, the secondary karyotype will be present only in part of the tissue and in some of the subsequently differentiating tissues (i.e., confined partial ICM mosaicism, confined partial TE mosaicism) (Figure 8.3d, e). This latest case is at the base of organ-specific mosaicism like confined placental mosaicism and germinal mosaicism.
Uncontrolled Oxygen Levels in Cultures of Retinal Pigment Epithelium: Have We Missed the Obvious?
Published in Current Eye Research, 2022
For cultures of RPE, cells are either obtained from dissected living tissue or cell lines. Early successful works began with embryonic chicks3 in the 1920th and extended to other non-human species (amphibians and animals) thereafter.4 From the 1960s, notable progress in cell culture technique, especially development of Eagle’s medium,44 has facilitated such in vitro studies. Since the 1970s, human RPE cultures, the best model system, have been in use. Currently two forms of them, fetal and adult, are in practice.45 However, obstacles including ethical considerations and limited access to human donors have encouraged the continuation of using human pluripotent stem cells as well as cells from non-human sources.4 The induced pluripotent stem cell-derived RPE (iPSC-RPE) is a promising alternative to human RPE for various applications such as genetic studies 46 and the development of cell-based regenerative therapies.47 It non-invasively yields unlimited number of cells with the same genetic background.46 Regarding non-human origin, one example is adult porcine RPE cells that can be used easily by bypassing ethical issues, postmortem time and accessibility/age of donors. Although these cells largely resemble adult human RPE cell culture, the porcine eye lacks macula or fovea.45
Bacteria and cells as alternative nano-carriers for biomedical applications
Published in Expert Opinion on Drug Delivery, 2022
Rafaela García-Álvarez, María Vallet-Regí
Up to the 20th century, medical procedures, such as blood transfusion, assisted fertility, or organ transplantation, have become common, as well as using functional tissue for treatment of several diseases. However, the use of donor tissue to treat medical problems was limited to like for like, for instance: blood for blood or skin for skin tissues until the beginning of the 21st century. This paradigm changed with the discovery and description of the ‘stem cells’ by Ernest McCulloch and James Till in the early 1960s [114]. Pluripotent stem cells have the potential of differentiating into many or any tissue type, which can nowadays be achieved owing to the development of the necessary tools for this purpose. These particular cell type is known to be a constituent of embryonic tissue and bone marrow, tissues that are particularly expensive and difficult to obtain. Due to their origin, stem cell use raises some ethical and legal questions regarding their collection and their utilization for commercial purposes [115]. Fortunately, these cells were acknowledged in another kind of tissue, which provided an alternative for the collection, manipulation, and potential use of stem cells – or other different types of undifferentiated cells – for alternative therapies avoiding the need of embryonic or bone marrow materials [116]. This leads to the possibility of commercialization at large scale of cell-therapy products.
Connexins in the development and physiology of stem cells
Published in Tissue Barriers, 2021
Anaclet Ngezahayo, Frederike A. Ruhe
In developing organisms, pluripotency is closed after the formation of the three germ cell layers during gastrulation, which correlates with the implantation of the embryo in the maternal endometrium. Further development is relayed to stem cells in the germ layers that produce cells solely of germ cell lineage to form different tissues and organs. These stem cells in germ layers can be considered as adult stem cells. In culture, EPSCs and iPSCs do not resume gastrulation. Cells can be primed to differentiate into specific germ layer cells as mentioned above for the primitive endoderm in embryoid bodies.121 Thereafter, the cells develop into adult somatic cells corresponding to the germ cell layer. EPSCs and iPSCs are therefore a convenient model to analyze the role of Cxs and GJIC in the development of all cell types. For the nervous system, which represents the ectodermal germ layer differently, Cxs are expressed in NSCs as discussed above.