The embryonic period
Frank J. Dye in Human Life Before Birth, 2019
Before the human embryo leaves the fallopian tube to enter the uterine cavity, it undergoes a stage referred to as the morula. The morula is a stage in animal development characterized by a solid ball of blastomeres (Figure 8.2). During mammalian development, blastomeres undergo a process called compaction. Until this stage, the individual blastomeres are easily discernible—like members of a cluster of grapes. During compaction, however, the association of the blastomeres becomes so intimate that it is no longer possible to make out the individual blastomeres using an ordinary light microscope. While the cells are intimately associated, they form among themselves two types of connections, or cell junctions. These cell junctions allow the next stage of development, the blastocyst, to emerge.
The Ultrastructure And Pathobiology Of Urinary Bladder Cancer
George T. Bryan, Samuel M. Cohen in The Pathology of Bladder Cancer, 2017
Intercellular junctions have been extensively characterized in transitional cell carcinomas. In general, the types of intercellular junctions observed in human and animal urinary bladder tumors are the same as those in normal bladder epithelium, namely, occludens, adherens, and gap junctions.31,58,82,,104,105,121,127,176,241,,268,295,296 However, each of these types of intercellular junctions can differ in tumors from its normal counterpart with respect to overall size, distribution at the cell surface, level of development, and numerical density.31,105,121,122,176,241,268,295,296 These differences may account for or contribute to some properties of malignant tumors, such as abnormalities in cell-to-cell adhesion,121,122 growth control,297 and transepithelial permeability.58,176 Three major types of cell junctions will be considered individually in the following sections.
Nasal Neuroblastomas in Man
Gerd Reznik, Sherman F. Stinson in Nasal Tumors in Animals and Man, 2017
Electron microscopy was performed on four tumors from this group, confirming that the cells were round to ovoid with scanty cytoplasm and few organelles. Chromatin was finely distributed and nucleoli were small and often not visible. Typically the nuclear profile was regular: invaginations were infrequent and jagged contours were rarely seen. The dominant ultrastructural finding was the presence of dendritic cytoplasmic processes that varied in number and caliber, and they were responsible for the fibrillary appearance seen by light microscopy between cells and at the core of rosettes. Accumulations of small dense-core granules, most of them less than 200 nm in diameter, were observed within the processes (Figure 2) and a few similar granules were occasionally present within the cytoplasm of the cell bodies. Cell junctions, typically confined to densities of the apposed plasma membranes of cell bodies or processes, were readily found. Longitudinally aligned microtubules were present in occasional processes but were much less numerous than in pediatric neuroblastomas that we have studied.
Cell-cell junctions: structure and regulation in physiology and pathology
Published in Tissue Barriers, 2021
Mir S. Adil, S. Priya Narayanan, Payaningal R. Somanath
Intercellular junctions are structurally and biochemically differentiated regions of the plasma membrane through which adjacent cells interact in a specific manner. These structures were originally identified and named according to their morphology and purported function.29 To retain barrier function and to prevent the invasion of pathogens and their rapid systemic spread, cell junctions need to be kept tight and repaired quickly after vessel rupture.30 There are three functional categories of cell junction: anchoring junctions; tight, or occluding, junctions, and gap (GJ), or permeable, junctions Figure 1.17,31,32 The AJs and desmosomes provide essential adhesive and mechanical properties that contribute to barrier function but do not seal the paracellular space,33 the TJs hold cells together and form a near leakproof intercellular seal by fusion of adjacent cell membranes34 since interactions between cells are important for the assembly and maintenance of three-dimensional tissues.35 The latter is a selectively permeable barrier that generally represents the rate-limiting step of paracellular transport.33 Many cell types also possess GJs, which allow small molecules to pass from one cell to the next through channels.34
Desmosomes undergo dynamic architectural changes during assembly and maturation
Published in Tissue Barriers, 2022
Reena R. Beggs, Tejeshwar C. Rao, William F. Dean, Andrew P. Kowalczyk, Alexa L. Mattheyses
Considering our data in the context of other epithelial junctions, we note that tight junctions and gap junctions are also known to undergo structural remodeling, although the underlying mechanisms have not been fully elucidated.37,38 The interplay between different cell junctions is complex, and junctions are historically studied in isolation, which makes investigating interactions between different cell junctions difficult.39 Signaling and colocalization have been previously implicated in communication between some junctions. One possible way that desmosomes could impact other junctions is through an interaction between desmoplakin and microtubule binding proteins.40,41 This has been demonstrated by a mutation in desmoplakin, which leads to aberrant targeting of gap junction proteins as a result of misregulation of microtubule dynamics.42 It is possible interactions with microtubule binding proteins that could be transmitted through architectural changes. The nature of junction architecture in different tissue types, and possible implications of architectural interactions between junctions, is a largely unexplored area with potential for great importance in understanding cell adhesion and communication.
Bridging the gap: Super-resolution microscopy of epithelial cell junctions
Published in Tissue Barriers, 2018
Emily I. Bartle, Tejeshwar C. Rao, Tara M. Urner, Alexa L. Mattheyses
Cell junctions are complex macromolecular structures with critical roles in many diverse processes including embryonic development, immune function, and wound healing. Epithelial tissues can have several types of cell junctions including tight junctions, adherens junctions, desmosomes, and gap junctions on the lateral membrane physically linking neighboring cells; and hemidesmosomes on the basal membrane interacting with the extracellular matrix (Fig. 1). Each of these junctions have highly specialized structures and cellular organization specific to their unique roles in signaling and adhesion,1 mechanobiology,2 and barrier formation,3 to name a few. Investigating the structure/function of cell junctions is challenging due to their membrane localization, molecular complexity, and size, which ranges from ∼10 nm (gap junctions) to ∼500 nm (desmosomes).4,5
Related Knowledge Centers
- Adherens Junction
- Cell Adhesion Molecule
- Desmosome
- Epithelium
- Gap Junction
- Paracellular Transport
- Protein Quaternary Structure
- Extracellular Matrix
- Cell
- Plasmodesma