Prenatal Development of the Facial Skeleton
D. Dixon Andrew, A.N. Hoyte David, Ronning Olli in Fundamentals of Craniofacial Growth, 2017
The concept of three primary germ layers is a time-honored one that has had a substantial influence on our knowledge of embryology. It provides an essential basis for our interpretation and understanding of the sequence of events by which tissues and organs undergo normal development. The establishment of germ layers may be thought of as the embryo’s way of sorting out its constituent parts (Oppenheimer, 1940). In fact, this is the basis of the gastrulation phase in other animal forms. Both actual and total developmental potentials may be attributed to the germ layers, the former being what the constituent cells become under normal circumstances, the latter representing a capability to form additional cells or tissues under either unusual or experimental circumstances (Brachet, 1935). Experimental studies have shown that the contributions by the three primary germ layers to tissues and organs is not as specific as was once thought. In this context, McCrady (1944) emphasized the need to recognize a clear distinction between prospective and definitive germ layers. While there may be a labile or flexible quality in the early precursors of the germ layers, there follows a “mosaic” stage when the fates of the layers are rigidly determined.
Current developments in human stem cell research and clinical translation
Christine Hauskeller, Arne Manzeschke, Anja Pichl in The Matrix of Stem Cell Research, 2019
In the following weeks specific organs and tissues arise from these germ layers such as epidermal and neuronal cells from ectoderm, cardiac and hematopoietic cells from mesoderm, and pancreatic and gastrointestinal cells from endoderm. During these processes, cells are continuously specialized to fulfil their later functions and thus they gradually lose differentiation potential. Along this development, multipotent stem cells can still differentiate into a variety of specialized cell types but this differentiation capacity is restricted to a specific lineage and/or organ. For example, hematopoietic stem cells can only differentiate into erythrocytes or leukocytes but not into hepatocytes. Thus, pluripotent stem cells are a transient cell population only found in the early phases of embryogenesis, while multipotent stem cells are found throughout adulthood in various tissues and organs and are responsible for replenishing adult cell pools. Therefore, they are also referred to as adult/tissue/organ-specific stem cells. Upon terminal differentiation, those cells lose their ability to give rise to more differentiated progeny and are then called unipotent or somatic cells (Figure 5.1).
The Many Faces of Neoplasia
Jeremy R. Jass in Understanding Pathology, 2020
Finally, it should be recalled that whilst mesoderm is associated with the various connective tissues of the body, a number of glandular organs or tissues are derived from this germ layer, for example the kidneys, the endometrial lining of the uterus and the mesothelium of serous membranes. Therefore it is only to be expected that neoplastic mesoderm should be capable of bidirectional differentiation to form both epithelial and connective tissues. Carcinomas of ectodermal or endodermal origin may rarely contain sarcomatous-appearing (malignant connective tissue) elements and have been described as carcinosarcomas. However, the behaviour of these tumours generally fits with the underlying carcinoma and not with the sarcomatous component.
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.
Advances in understanding vertebrate nephrogenesis
Published in Tissue Barriers, 2020
Joseph M. Chambers, Rebecca A. Wingert
Vertebrate development entails the formation of three germ layers, the ectoderm, mesoderm, and endoderm, which provide cellular blueprints for embryonic organogenesis. Ectoderm gives rise to the central nervous system and skin cells, and endoderm derivatives encompass cells that line the respiratory and digestive tracts. The mesoderm, or middle layer, produces cells that are most abundant in the human body constituting skeletal muscle, cartilage, heart, gonads, and blood, among other tissue types.1 This review will focus on a member of the mesoderm lineage: the kidney. Much of our understanding about kidney development stems from rodent models, but also has benefited from studies in other vertebrates such as fish, frogs, and birds.2The inception of mesoderm development begins with the differentiation of pluripotent epiblast cells into a transient ‘primitive streak’ zone.1Position along the anterior-posterior embryonic axis and other instructive signals regulate the regionalization of paraxial, intermediate, and lateral plate mesoderm.3
Stiffness estimation of transversely anisotropic materials using a novel indentation tester with a rectangular hole
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Atsutaka Tamura, Mika Saiki, Jun-ichi Hongu, Takeo Matsumoto
Gastrulation is an essential step in the development of most animals. This process is fundamental to vertebrate animals, and it is the early developmental stage in which a single layer of cells gives rise to multiple germ layers, enabling the differentiation of the internal tissues of the body (Gilbert 2014; Urry et al. 2016); in other words, the body plan of the animal embryo is shaped through the process of gastrulation. In mammals, a cascade of morphogenesis-related molecular events, e.g. polarization, intercalation, and intercellular adhesion, occurs in specific embryonic territories although knowledge about how the territories grow physically and remodel has remained elusive. Thus, characterization of the early developmental process during gastrulation is important to accurately describe the precise timing of cell-type specification.