Cyclic mechanical pressure-loading alters epithelial homeostasis in a three-dimensional in vitro oral mucosa model: clinical implications for denture-wearers

Denture-wearing affects the quality and quantity of epithelial cells in the underlying healthy oral mucosa. The physiologic mechanisms, however, are poorly understood. This study aimed to compare histologic changes and cellular responses of an epithelial cell layer to cyclic mechanical pressure-loading mimicking denture-wearing using an organotypic culture system to develop a three-dimensional in vitro oral mucosa model (3DOMM). Primary human oral keratinocytes and fibroblasts were serially grown in a monolayer culture, and cell viability was measured under continuous cyclic mechanical pressure (50 kPa) for 7 days (cycles of 60 min on, 20 s off to degas and inject air). Upon initiation of an air-liquid interface culture for epithelial stratification, the cyclic pressure, set to the mode above mentioned, was applied to the 3DOMMs for 7 days. Paraffin-embedded 3DOMMs were examined histologically and immunohistochemically. In the monolayer culture, the pressure did not affect the viability of oral keratinocytes or fibroblasts. Few histologic changes were observed in the epithelial layer of the control and pressure-loaded 3DOMMs. Immunohistochemical examination, however, revealed a significant decrease in Ki-67 labelling and an increase in filaggrin and involucrin expression in the suprabasal layer of the pressure-loaded 3DOMMs. Pressure-loading attenuated integrin β1 expression and increased matrix metalloproteinase-9 activity. Incomplete deposition of laminin and type IV collagen beneath the basal cells was observed only in the pressure-loaded 3DOMM. Cyclic pressure-loading appeared to disrupt multiple functions of the basal cells in the 3DOMM, resulting in a predisposition towards terminal differentiation. Thus, denture-wearing could compromise oral epithelial homeostasis.

Morphology of isolated Gli349, a leg protein responsible for Mycoplasma mobile gliding via glass binding, revealed by rotary shadowing electron microscopy

Several species of mycoplasmas rely on an unknown mechanism to glide across solid surfaces in the direction of a membrane protrusion at the cell pole. Our recent studies on the fastest species, Mycoplasma mobile, suggested that a 349-kDa protein, Gli349, localized at the base of the membrane protrusion called the neck, forms legs that stick out from the neck and propel the cell by repeatedly binding to and releasing from a solid surface, based on the energy of ATP hydrolysis. Here, the Gli349 protein was isolated from mycoplasma cells and its structure was analyzed. Gel filtration analysis showed that the isolated Gli349 protein is monomeric. Rotary shadowing electron microscopy revealed that the molecular structure resembles the symbol for an eighth note in music. It contains an oval foot 14 nm long in axis. From this foot extend three rods in tandem of 43, 20, and 20 nm, in that order. The hinge connecting the first and second rods is flexible, while the next hinge has a distinct preference in its angle, near 90 degrees. Molecular images revealed that a monoclonal antibody that can bind to the position at one-third of the total peptide length from the N terminus bound to a position two-thirds from the foot end, suggesting that the foot corresponds to the C-terminal region. The amino acid sequence was assigned to the molecular image, and the topology of the molecule in the gliding machinery is discussed.

Identification of a 123-kilodalton protein (Gli123) involved in machinery for gliding motility of Mycoplasma mobile

Mycoplasma mobile glides on a glass surface in the direction of its tapered end by an unknown mechanism. Two large proteins, Gli349 and Gli521, were recently reported to be involved in glass binding and force generation/transmission, respectively, in M. mobile gliding. These proteins are coded tandemly with two other open reading frames (ORFs) in the order p123-gli349-gli521-p42 on the genome. In the present study, reverse transcriptase PCR analysis suggested that these four ORFs are transcribed cistronically. To characterize the p123 gene coding a 123-kDa protein (Gli123) of 1,128 amino acids, we raised polyclonal antibody against the Gli123 protein. Immunoblotting for Gli123 revealed that Gli123 was missing in a mutant strain, m12, which was previously isolated and characterized by a deficiency in glass binding. Sequencing analysis showed a nonsense mutation at the 523rd amino acid of the protein in the m12 mutant. Immunofluorescence microscopy with the polyclonal antibody showed that Gli123 is localized at the head-like protrusion's base, the cell neck, which is specialized for gliding, as observed for Gli349 and Gli521. Localization of the gliding proteins, Gli349 and Gli521, was disturbed in the m12 mutant, suggesting that Gli123 is essential for the positioning of gliding proteins in the cell neck.

Gliding ghosts of Mycoplasma mobile

Several species of mycoplasmas glide on solid surfaces, in the direction of their membrane protrusion at a cell pole, by an unknown mechanism. Our recent studies on the fastest species, Mycoplasma mobile, suggested that the gliding machinery, localized at the base of the membrane protrusion (the "neck"), is composed of two huge proteins. This machinery forms spikes sticking out from the neck and propels the cell by alternately binding and unbinding the spikes to a solid surface. Here, to study the intracellular mechanisms for gliding, we established a permeabilized gliding ghost model, analogous to the "Triton model" of the eukaryotic axoneme. Treatment with Triton X-100 stopped the gliding and converted the cells to permeabilized "ghosts." When ATP was added exogenously, approximately 85% of the ghosts were reactivated, gliding at speeds similar to those of living cells. The reactivation activity and inhibition by various nucleotides and ATP analogs, as well as their kinetic parameters, showed that the machinery is driven by the hydrolysis of ATP to ADP plus phosphate, caused by an unknown ATPase.

Identification of a 521-kilodalton protein (Gli521) involved in force generation or force transmission for Mycoplasma mobile gliding

Several mycoplasma species are known to glide on solid surfaces such as glass in the direction of the membrane protrusion, but the mechanism underlying this movement is unknown. To identify a novel protein involved in gliding, we raised monoclonal antibodies against a detergent-insoluble protein fraction of Mycoplasma mobile, the fastest glider, and screened the antibodies for inhibitory effects on gliding. Five monoclonal antibodies stopped the movement of gliding mycoplasmas, keeping them on the glass surface, and all of them recognized a large protein in immunoblotting. This protein, named Gli521, is composed of 4,738 amino acids, has a predicted molecular mass of 520,559 Da, and is coded downstream of a gene for another gliding protein, Gli349, which is known to be responsible for glass binding during gliding. Edman degradation analysis indicated that the N-terminal region is processed at the peptide bond between the amino acid residues at positions 43 and 44. Analysis of gliding mutants isolated previously revealed that the Gli521 protein is missing in a nonbinding mutant, m9, where the gli521 gene is truncated by a nonsense mutation at the codon for the amino acid at position 1170. Immunofluorescence and immunoelectron microscopy indicated that Gli521 localizes all around the base of the membrane protrusion, at the "neck," as previously observed for Gli349. Analysis of the inhibitory effects of the anti-Gli521 antibody on gliding motility revealed that this protein is responsible for force generation or force transmission, a role distinct from that of Gli349, and also suggested conformational changes of Gli349 and Gli521 during gliding.

Sequence analysis of the gliding protein Gli349 in Mycoplasma mobile

The motile mechanism of Mycoplasma mobile remains unknown but is believed to differ from any previously identified mechanism in bacteria. Gli349 of M. mobile is known to be responsible for both adhesion to glass surfaces and mobility. We therefore carried out sequence analyses of Gli349 and its homolog MYPU2110 from M. pulmonis to decipher their structures. We found that the motif “YxxxxxGF” appears 11 times in Gli349 and 16 times in MYPU2110. Further analysis of the sequences revealed that Gli349 contains 18 repeats of about 100 amino acid residues each, and MYPU2110 contains 22. No sequence homologous to any of the repeats was found in the NCBI RefSeq non-redundant sequence database, and no compatible fold structure was found among known protein structures, suggesting that the repeat found in Gli349 and MYPU2110 is novel and takes a new fold structure. Proteolysis of Gli349 using chymotrypsin revealed that cleavage positions were often located between the repeats, implying that regions connecting repeats are unstructured, flexible and exposed to the solvent. Assuming that each repeat folds into a structural domain, we constructed a model of Gli349 that fits well the shape and size of images obtained with electron microscopy.

228 EXPRESSION OF zag1 IN MOUSE PRE-IMPLANTATION EMBRYOS

Embryonic gene activation (EGA) first occurs during the second half of the mouse 1-cell embryo (Latham KE 1999 Int. Rev. Cytol. 193, 71–124). Moreover, precise regulation of EGA is considered to be essential for normal embryo development. To understand the molecular basis for the regulation of EGA, we have focused on the identification and functional characterization of genes activated at the late 1-cell stage of the mouse embryo. Recently, we have identified and isolated a novel gene, termed zag1 (zygotic activating gene 1), transcribed specifically at the EGA, using a fluoro-differential display method with oocytes and embryos at 15 h post-insemination. Messenger RNA of zag1 expressed at lower level in the oocyte than that in the embryo at 15 h post-imsemination. In this study, we investigated the potential function of zag1 by analysis of mRNA expression and protein distribution in mouse tissues and pre-implantation embryos. Nucleotide sequence analysis of zag1 cDNA revealed that the open reading frame of 1726 bps encodes a protein of 575 amino acids with a predicted molecular mass of 66 kDa. The deduced amino acid sequence indicated that zag1 protein might be a soluble protein with a bipartite nuclear targeting sequence, a NACHT NTP domain, and an APT/GTP binding site motif as a predicted functional domain. Two μg of Poly(A)+ RNA from various tissues of adult mice were subjected to Northern blot analysis using the mouse zag1 cDNA probe. We detected this gene abundantly expressed in mouse testis and ovary by approximately 2- to 3-fold compared with one in other mouse tissues (heart, liver, kidney, lung, brain, skeletal muscle, and spleen). zag1 transcript and protein, as assessed by RT-PCR and immunoblotting, respectively, were slightly present in ovulated oocytes, gradually decreased in the early 1-cell embryos, but re-expressed in the late 1-cell and early 2-cell stage embryos which coincided with the mouse EGA. Subsequent to microinjection of an expression vector encoding zag1-enhanced green fluorescent protein (EGFP), fused protein into male pronucleus of 1-cell embryos was detected in the nuclei of 2-cell embryos. These findings suggest that zag1 may be functionally associated with early embryonic development. This study was supported by a Grant-in-Aid for the 21st Century COE Program of the Japan MEXT, and by a grant from the Wakayama Prefecture Collaboration of Regional Entities for the Advancement of Technological Excellence of the JST.

Identification of a 349-kilodalton protein (Gli349) responsible for cytadherence and glass binding during gliding of Mycoplasma mobile

Several mycoplasma species are known to glide in the direction of the membrane protrusion (head-like structure), but the mechanism underlying this movement is entirely unknown. To identify proteins involved in the gliding mechanism, protein fractions of Mycoplasma mobile were analyzed for 10 gliding mutants isolated previously. One large protein (Gli349) was observed to be missing in a mutant m13 deficient in hemadsorption and glass binding. The predicted amino acid sequence indicated a 348,758-Da protein that was truncated at amino acid residue 1257 in the mutant. Immunofluorescence microscopy with a monoclonal antibody showed that Gli349 is localized at the head-like protrusion's base, which we designated the cell neck, and immunoelectron microscopy established that the Gli349 molecules are distributed all around this neck. The number of Gli349 molecules on a cell was estimated by immunoblot analysis to be 450 +/- 200. The antibody inhibited both the hemadsorption and glass binding of M. mobile. When the antibody was used to treat gliding mycoplasmas, the gliding speed and the extent of glass binding were inhibited to similar extents depending on the concentration of the antibody. This suggested that the Gli349 molecule is involved not only in glass binding for gliding but also in movement. To explain the present results, a model for the mechanical cycle of gliding is discussed.

Movement on the cell surface of the gliding bacterium, Mycoplasma mobile, is limited to its head-like structure

Mycoplasma mobile cells glide on solid surfaces such as glass with a fast and continuous motion in the direction of the membrane protrusion (head-like structure) at one cell pole. To examine its cell-surface movement, a latex bead was attached to a cell and behavior in gliding was monitored. The bead was carried without movement relative to the cell body, suggesting that the cell does not roll around the cell axis and the surface movement is limited to a small area. A small percentage of cells showed an elongated head-like structure in an old batch culture. The head-like structure moved forward, sometimes leaving the cell body in one position, resulting in a stretching of this head-like structure. These results indicate that the head-like structure drags the cell body, leading us to conclude that the force for gliding is generated at the head-like structure.

Gliding mutants of Mycoplasma mobile: relationships between motility and cell morphology, cell adhesion and microcolony formation

The present study characterizes gliding motility mutants of Mycoplasma mobile which were obtained by UV irradiation. They were identified by their abnormal colony shapes in 0.1% agar medium, showing a reduced number of satellite colonies compared to the wild-type. A total of ten mutants were isolated based on their colony phenotype. Using dark-field and electron microscopy, two classes of mutants, group I and group II, were defined. Cells of group I mutants had irregular, flexible and sometimes elongated head-like structures and showed a tendency to aggregate. Neither binding to glass nor gliding motility was observed in these mutants. Cells of group II mutants were rather spherical in shape, with the long axis reduced to 80% and the short axis enlarged to 120% of that of wild-type cells, respectively. Their gliding speed was 20% faster than that of wild-type cells. Three of the ten mutants remained unclassified. Mutant m6 had a reduced binding activity to glass and a reduced gliding motility with 50% of the speed of the wild-type strain. The ability of wild-type and mutant colonies to adsorb erythrocytes was found to correlate with the binding activity required for gliding, indicating that mycoplasma gliding depends on cytadherence-associated components. Finally, the ability to form microcolonies on surfaces was shown to correlate with the gliding activity, suggesting a certain role of gliding motility in the parasitic life-cycle of mycoplasmas.

Muscle activities in the hand and arm during tooth brushing and the regulation of brushing movements by oral sensory perception

Investigations were made of the forces during brushing of the teeth, the patterns of brushing movements, and muscle activities, with and without blockage of sensory perception in the oral cavity, while each subject brushed by the rolling method, scrubbing method, and by his own individual habitual brushing method. We learned from electromyograms that the scrubbing method primarily used the muscles of the palm of the hand and the forearm, while the rolling method cleaned principally by action of the muscles of the upper arm and shoulder. With the rolling method, the rhythmic pattern of the brushing movement and muscle activity were lost when sensory perception in the oral cavity was blocked and, in those subjects who had a low periodontal membrane tactile threshold, the brushing force was greater than when sensory perception was not blocked. However, no effect was observed with blockage of the sensory perception in the oral cavity when the scrubbing method was used. Since brushing movements with the scrubbing method resemble the movements of writing, we also carried out investigations on the relationship between the forces during writing and brushing. As a result we found that with the scrubbing method, the brushing forces were strong for the subjects who had strong writing forces, while they were weak for those with weak writing forces. It was clear from the above results that the force of brushing with the rolling method was affected more by factors relating to oral sensory perception than muscle activity, while with the scrubbing method it was affected more by factors relating to muscle activity of the palm of the hand and forearm than by oral sensory perception. There was a clear difference in the brushing forces, pattern of brushing movements, and muscle activity between experienced and inexperienced subjects with both the scrubbing and rolling methods. Thus we learned that the effect of brushing instructions could be evaluated not only by the efficiency of plaque removal, brushing force or skill of brushing movements, but also by muscle activity. The phenomena observed with the scrubbing and rolling methods were not seen with the subjects' individual habitual brushing method.