Types Of Cell Contacts Research Articles

The elementary fusion modalities of osteoclasts

The last step of the osteoclast differentiation process is cell fusion. Most efforts to understand the fusion mechanism have focused on the identification of molecules involved in the fusion process. Surprisingly, the basic fusion modalities, which are well known for fusion of other cell types, are not known for the osteoclast. Here we show that osteoclast fusion partners are characterized by differences in mobility, nuclearity, and differentiation level. Our demonstration was based on time-laps videos of human osteoclast preparations from three donors where 656 fusion events were analyzed. Fusions between a mobile and an immobile partner were most frequent (62%), while fusion between two mobile (26%) or two immobile partners (12%) was less frequent (p<0.001). In general, the immobile fusion partner contained more nuclei than the mobile one (p<0.01). Furthermore, enrichment in nuclei of an osteoclast with three or more nuclei resulted from fusion with a mono-nucleated cell in 67% of the cases (p<0.001), while mono-nucleated cells fused with a multinucleated cell in 61% of the cases (p<0.05). This observation suggested that a more mature osteoclast prefers to fuse with a less mature pre-osteoclast. This hypothesis was supported by a nucleus-tracing approach in a co-culture of more and less differentiated pre-osteoclasts/osteoclasts. Furthermore, we found that osteoclast fusion proceeds through primarily two different types of cell contacts: phagocytic-cup and broad-contact-surfaces (>80% of all fusions). We conclude that osteoclasts most often gain nuclei by addition of one nucleus at a time, and that this nucleus is most often delivered by a moving cell to an immobile cell. These characteristics fit the in vivo observations where mono-nucleated precursors migrating from the bone marrow fuse with more mature osteoclasts sitting on the bone surface. They also fit the fusion modalities of other cell types.

Fine structure of the ciliated cells and ciliary rootlets of Intoshia variabili (Orthonectida)

The body of the Intoshia variabili (Orthonectida) is covered by a layer of alternating rings of flattened ciliated and non-ciliated cells, covered by a thin 0.25- to 0.30-µm cuticular layer. Ciliated cells bear rows of cilia, with five to seven cilia in each row. The kinetosome of each cilium is situated in a small pit and bears two identical cross-striated rootlets oriented along the longitudinal axis of the body and parallel to the cell surface. Two types of cell contacts are present between these cells, spot desmosomes and tight junctions. Two fibrous bands, an anterior and a posterior one, both running parallel to the cell surface, are always present in the apical part of both the ciliated and the non-ciliated cells. These fibrous bands are not only attached to the desmosomes between the cells within a ring but also connect them, traversing the cell. Thus, two fibrous rings are formed within every ring of ciliated and non-ciliated cells. The rootlets of the cilia closest to the fibrous band are connected with the bands. These bands of filaments and the associated rootlets form a unique structure for the orthonectids. The phylogenetic relationships of Orthonectida are considered on the basis of this new information. The hypothesis that Orthonectida are derived Annelida or at least derived Trochozoa has gained support based mainly on the new ultrastructural data, such as the true cuticle and fibrous bands in the epithelial cells consisting of ciliated and non-ciliated cells.

MHC regulation in neural cells. Distribution of peripheral and internal beta 2-microglobulin and class I molecules in human neuroblastoma cell lines.

mAb were used in an immunocytochemical assay to examine beta 2-microglobulin (b2-m) and class I MHC expression in human neuroblastoma cell lines. In lines with weak class I expression among the whole population, under ordinary assay conditions, strong b2-m and class I expression were concentrated in a small subpopulation. In positive cells, Ag was not restricted to any part of the cell body or processes. Strong expression was not required for establishment of any morphologic form or any type of cell contact. These findings complement studies in other experimental systems, where a nonimmunologic role for class I or b2-m in neural cell growth was not revealed. When the microscopic assay was modified to reveal Ag within the internal membrane system, b2-m was detected in every neuroblastoma cell. Most often, the Ag appeared as a ring around the nucleus, or in a punctate distribution in the juxtanuclear area. Internal expression of HLA chains and class I molecules was more difficult to detect, possibly reflecting a normal excess of b2-m. These findings increase understanding of MHC regulation in neural cell lines. They provide the technical and conceptual background for examination of internal MHC Ag in neural tissue.

Mutual contact of murine erythroleukemia cells activates depolarizing cation channels, whereas contact with extracellular substrata activates hyperpolarizing Ca2+‐dependent K+ channels

This study deals with the modulation of the plasma membrane potential (delta psi p) of murine erythroleukemia (MEL) cells by cell-substratum or cell-cell contact. delta psi p was determined by measuring the distribution of tetraphenylphosphonium (TPP+) across the plasma membrane; it appeared strongly, and inversely, influenced by the two types of cell contacts. Contact with the culture surface produced a delta psi p hyperpolarization directly proportional to average distance among the ideal centers of the cells on this surface (d) within the range 10-80 microns. A detailed mathematical analysis of the function delta psi p = f(d) is presented, as well as experiments involving the use of ionophores (valinomycin and A23187) and the conditioning of the culture surface. We concluded that the d-dependent hyperpolarization (dDH) was the result of a complex interplay between the activating properties of substratum on Ca2+-dependent K+ channels (KCa) and some substratum-adherent factors that are shed by MEL cells and antagonize KCa activation (substratum-attached cellular factors = SACF). By contrast, contact of the cells with each other, obtained by incubating MEL cells at d smaller than the average cell diameter (phi = 10 microns), produced a marked delta psi p depolarization. This intercellular contact-dependent depolarization (ICDD) was unaffected by valinomycin; it was abolished by substituting Na+ in the external medium with a nondiffusible cation (choline), which shows that ICDD was sustained by Na+ influxes, probably mediated by stretch-activated (s.a.) cation channels.

Contact relationships between vascular smooth muscle cells: an in vivo and in vitro study.

Cell/cell contacts in the intact media of the rat thoracic aorta and inferior vena cava, and in cultured smooth muscle cells from these vessels have been quantified in order to determine whether their density and their type can be correlated with the differences in load at these two sites. The type and number of contacts per 100 microns of cell perimeter and per 100 cells were determined with a semi-automatic image analysis system. In all cases there was a predominance of simple appositions; intermediate junctions, interdigitations, and nexus junctions were less frequently observed. There were more cell contacts of each type in the intact arteries than in the intact veins. In cell cultures, all types of cell contacts were increased but the proportion of load bearing types was reduced.

Cell junctions and other membrane specializations in the ocellus of the wasp, Paravespula Germanica L. (Hymenoptera : Vespidae)

Five types of cell contacts and other membrane specializations were found in the ocellus of the adult wasp, Paravespula germanica L. (Hymenoptera : Vespidae), based on freeze-fracture replicas and thin sections. Septate junctions alongside small gap junctions are present between iris cells and between corneagenous cells. Gap junctions are sometimes observed between glial cell processes. Photoreceptor cells and glial cells are frequently connected by scalariform junctions. Tight junction-like structures are found on receptor-cell membranes near rhabdomeric microvilli. Desmosomes are widespread in the ocellus, connecting iris cells, corneagenous cells, receptor cells, and glial cell processes. Desmosomes are found next to septate junctions. Glial membranes connected to receptor cells have a non-junctional type of membrane specializations, consisting of intramembraneous particles arranged in a rhombic pattern. Interestingly, both particle arrays and scalariform junctions are often adjacent to each other. Furthermore, a conspicuous modification of the cell surface in freeze cleaved cells is seen between adjacent glial cells intermediating two receptor cells.

Types of cell contacts in different smooth muscles

It is generally agreed that, where present, gap junctions or nexuses provide low-resistance pathways for cell-to-cell coupling of activity. Though these contacts were first described in smooth muscle and occur widely there, some types of smooth muscle contain few or no gap junctions, and many contain other types of contacts.A variety of smooth muscles from several species was fixed with phosphate-buffered glutaraldehyde by intra-arterial perfusion or by immersion of small strips. Samples were prepared for electron microscopy by standard methods, using oriented embedding to view muscle in both longitudinal and cross sections.Four types of cell contacts were identified in various smooth muscles, which have been previously recognized. 1) The gap junction or nexus appears with the usual double staining as a five-layered contact, often with adjacent clear areas of cytoplasm (Fig. 1).

Types of cell contacts in arterial smooth muscle.

Nachweis, dass in Arteriolen sowie in prakapillaren Arteriolen des Hunde-Duodenums nur eine einfache Aneinanderlagerung der Muskelzellen erfolgt und keine “gap junctions”, wie sie in den Muskelschichten der Hohlwandorgane vorhanden sind.

Reconstitution of the thymus dependent area in the spleen of lethally irradiated mice. A light and electron microscopical study of the T-cell microenvironment.

To study the submicroscopical morphology of the microenvironment for T-lymphocytes in the spleen, mice were lethally X-irradiated and injected intravenously with syngeneic thymocytes. 24 hours after cell transfer, small lymphocytes occurred in the thymus dependent area of the spleen: the periarteriolar lymphatic sheath (PALS). They localized preferentially around a special type of mononuclear phagocyte, the Interdigitating Cell (IDC), which is considered to be characteristic for thymus-dependent areas in peripheral lymphoid organs. A close cell contact between both cell types was observed: small lymphocytes protruded into the cytoplasm of the IDC by means of fingerlike protrusions. This type of cell contact seems to induce blast transformation of the lymphoid cells which resulted in the formation of medium sized T-cells. In a control experiment, spleen cells from thymectomized, X-irradiated and bone marrow reconstituted mice were injected intravenously into lethally X-irradiated recipients. These B-lymphocytes, however, were not found to be localized around IDC. They preferentially formed primary follicles at the periphery of lymphocyte-depleted thymus dependent areas.

A distinctive cell contact in the rat adrenal cortex.

Extensive cell contacts which resemble septate junctions occur between cells in the three major zones of the rat adrenal cortex. Characteristically, they extend between small intercellular canaliculi and the periendothelial space, frequently interrupted by gap junctions and rarely by desmosomes. Zonulae occludentes have not been identified in the adrenal cortex. Along this distinctive cell contact, the cell membranes of apposing cells are separated by 210-300 a bisected by irregularly spaced 100-150-A extracellular particles which are often circular in profile. In lanthanum preparations, these particles appear to form a continuous chain throughout the intercellular space and are visualized as an alveolate structure in sections parallel to the plane of the cell membrane. The cell membrane in the area of septate-like contact does not differ from nonjunctional areas of the cell membrane in freeze-fracture replicas. The cell contact retains its integrity after cell dispersion and after the separation of cell membranes from disrupted cells. The intercellular particles also persist after brief extraction in lipid solvents. Besides adherence, possible functions of this adrenal contact include maintenance of the width of the extracellular space, the provision of channels between intercellular canaliculi and the bloodstream, and utilization as cation depots. Similar structures are also present between adrenal cortical cells of several other species and between interstitial cells of the testis. This type of cell contact may, in fact, be a typical feature of steroid-hormone-secreting tissues in vertebrates.

An electron microscopical study of cell contacts in the seminiferous tubules of some mammals.

Different types of cell contacts in the seminiferous tubules have been studied electron microscopically in some laboratory and domestic mammals. Specialized inter-Sertoli cell contacts are always present. Most of them show a narrow — partly perhaps closed — intercellular space at some distance from the basement membrane, above the spermatogonia but below the spermatocytes. Fibrillar material is present in the cytoplasm near the junction as well as subsurface cisterns of the endoplasmic reticulum. Two main types of narrow junctions and one wide junction are described. These junctions are interpreted as devices for adhesion and perhaps intercommunication between the basal parts of the Sertoli cells. The narrow junctions are also considered to impede the intercellular transport of substances to spermatocytes and spermatides and into the luminal fluid. This interpretation emphasizes the importance of the Sertoli cells as nurse cells for the spermatocytes and spermatids.