In situ localization of F-actin in the normal and injured guinea-pig tympanic membrane

Actin cytoskeleton regulates Hippo signaling

Hippo pathway controls the organ size by modulating cell proliferation and apoptosis. However, the upstream regulation of hippo signaling by actin cytoskeleton is not clear. To elucidate the role of actin as an upstream regulator of Hippo signaling, the levels of F (filamentous)-actin in cells were elevated using jasplakinolide, an actin-stabilizing drug. Induction of F-actin formation in HeLa cells resulted in decreased phosphorylation of YAP, a key effector molecule for Hippo signaling. The activated YAP is localized to the cell nucleus and YAP increase was associated with increased expression of downstream CCN growth factors CCN1/CYR61 and CCN2/CTGF. The effect of the actin-stabilizing drug was blocked when YAP levels were suppressed in YAP “knock-down” cells. In summary, using an actin-stabilizing drug we show that actin cytoskeleton is one of the upstream regulators of Hippo signaling capable of activating YAP and increasing its downstream CCN growth factors.

Chronic tympanic membrane perforation: a better animal model is needed

Developments in the treatment of chronic tympanic membrane perforation have been hindered by the lack of an ideal animal model. It is not appropriate to test such treatments on acute perforations as the majority of these heal spontaneously. An ideal animal model would be one that most closely resembles the human clinical situation. It should be inexpensive, readily available, and easy to create. There have been a number of attempts to create a chronic tympanic membrane perforation model with limited success. All published attempts at chronic tympanic membrane perforations have been reviewed and the limitations of each model are discussed. A number of areas for research exist for further developing a chronic tympanic membrane perforation model. These areas include a perforation model in the presence of bacteria and eustachian tube dysfunction. Understanding the molecular and genetic mechanisms of chronic otitis media and potential treatments will also be useful.

Overlay versus underlay tympanoplasty. Part I: historical review of the literature

The history of otology is the history of the successful treatment of infections of the middle ear and the eardrum. Otologists have sought to restore hearing lost to infections of the eardrum since the 1600s. The development of instruments, techniques, and materials to treat infection is fascinating because of the serendipitous nature of the discoveries and the insight of the discoverers. This historical review describes the history of the treatment of infections of the ear and the development of modern techniques of ear surgery. Two contemporary methods of tympanic membrane repair are then described.

Epithelial migration in mastoid cavities

The epithelial migration in 18 dry ears with a cavity after surgery was studied by the ink-dot method and compared with the epithelial migration in 15 normal ears. A qualitatively normal centrifugal migration pattern was observed in all cavity ears. Considerable variation in migration speed was observed within the same cavity ear, thus a comparison with the migration speed in normal ears was impossible. No definite relationship was apparent between migration speed and the self-cleansing ability of the ear, which primarily appeared to be a function of the macroscopic appearance of the cavity (i.e. the presence of pockets or ridges). We conclude that epithelial migration is as important in maintaining the self-cleansing function and non-infected state in cavity ears as it is in normal ears.

Squamous Epithelium in the Middle Ear and Sinus

This study has been performed between December 1990—March 1991 in the Microsurgery laboratory of the Marmara University Hospital. Twelve healthy albino guinea pigs were used as a study group while the control group consists of three animals. The potentials for cholesteatoma formation of the squamous epithelium, namely the squamous epithelium of the posterior superior part of the external ear canal skin and normal skin, were investigated. Among 24 subjects who were implanted by canal skin, cholesteatoma was fanned in 21 of them. Likewise, 19 of 24 animals implanted by normal skin came out with cholesteatoma formation. Between these two types of epithelium, there is no statistical difference in cholesteatoma formation (p >0.5).

Patterns of epithelial migration in the unaffected ear in patients with a history of unilateral cholesteatoma

Epithelial migration in a centrifugal manner is an established phenomenon in the normal human tympanic membrane. This pattern of migration is symmetrical in both ears of any one individual. We present a prospective study on the pattern of tympanic ink dot migration on the normal drum, in patients with a history of cholesteatoma in one ear. It was demonstrated that patients who develop cholesteatoma have a normal migratory pattern and rate in the unaffected ear. The conclusion from this study is that defective migration is not the initiating factor in the development of acquired cholesteatoma.

Cytoskeletal organization of migrating retinal pigment epithelial cells during wound healing in organ culture

Retinal pigment epithelial (RPE) cells maintained in organ culture on Bruch's membrane and the associated choroid spread and migrate into a linear wound along the exposed basal lamina. Changes in cell shape, in the organization of microfilaments, and in cell-cell and cell-substratum interactions during this time were examined by epifluorescence and transmission electron microscopy. In contrast to cuboidal stationary cells distant from the wound edge, which display well-developed apical circumferential microfilament bundles (CMBs) associated with zonulae adhaerentes junctions, the migrating RPE cells near the wound edge instead are flat, and, in addition to microfilament bundles near junctions between adjacent cells, display prominent stress fibers. Furthermore, monoclonal antibodies to vinculin labeled regions at the terminal ends of these stress fibers indicating that the RPE cells form focal contacts with the basal lamina at these sites. Electron microscopy of these regions of cell-substratum interaction confirmed the presence of microfilament bundles that terminate on the cell membrane. Folds present in the basal lamina near these sites suggest that tension is being generated by the microfilaments in the stress fibers as the migrating cells pull on the underlying basal lamina through these adhesion points.

Migration-related changes in the cytoskeleton of cultured neural crest cells visualized by the monoclonal antibody I-5G9

An epitope recognized by the monoclonal antibody I-5G9 was expressed by all neural crest cells shortly after explantation into culture. At this time all neural crest cells actively migrated away from the neural tube. Immunoreactivity was localized intracellularly and organized into stress fiber-like filaments. Often, immunofluorescence was particularly high in short fibers in the lamellipodia of the leading edge of migrating cells. Two-week-old cultures had a diameter of 8-10 mm. At that stage a ring of immunoreactive cells was present at the periphery of each culture, an area where cells were still migratory. An inner concentric circle had reduced and more granular staining. In this area cells had ceased to migrate. In the center of the culture cells were multilayered, nonmigratory, and did not bind I-5G9. After creating a lesion in the nonreactive central region, some cells resumed migration into the lesioned area and reexpressed the epitope. I-5G9 staining and phalloidin fluorescence colocalized partially in some cells and completely in others. It is concluded that the epitope recognized by I-5G9 is expressed in a migration-dependent manner. The partial colocalization of I-5G9 and phalloidin fluorescence supports the notion that the epitope recognized by I-5G9 is specifically expressed in stress fibers of migratory cells, possibly in one of the actin-associated proteins or an F actin-associated protein complex.

Short-term effects of iontophoresis on the structure of the guinea pig tympanic membrane

Guinea pig tympanic membrane was anesthetized iontophoretically. The animals were sacrificed between 2 h and 4 days after the anesthesia and the tympanic membrane was studied histologically by light microscopy and transmission electron microscopy. Edema in the subepidermal connective tissue layer and detachment of the basement membrane from the basal cell layer were observed 2 h after iontophoresis. Eight and 12 h later, the epidermal layer between the handle of the malleus and the bony annulus peeled and retracted towards the bony annulus, leaving only hornified outer epidermis on the fibrous layer. Four days after iontophoresis, the retracted margin of the epidermal layer became greatly thickened and evidence of hyperplasia and migration was observed. This study has demonstrated that iontophoresis of the tympanic membrane produces remarkable histological changes. However, no perforation was observed.