Comparison of posterior alveolar canal location measured on computer tomography scan with cadaveric measurement of posterior superior alveolar foramen in Japanese samples

The aim of this study was to analyse anatomical characteristics of the most posterior alveolar canal (PAC) on computed tomography (CT) images and the posterior superior alveolar foramen (PSAF) physically identified in cadaveric samples, to avoid injuring the posterior superior alveolar artery (PSAA) during surgery in the maxillary tuberosity region. The study included 125 hemi-heads of 64 Japanese cadavers. Simple CT data of the maxillary bone region of the samples were obtained and analysed using measurement software. The alveolar crest (AC) and the PAC were identified to calculate the shortest distance between the AC and the PAC (AC-PAC). Then the samples were dissected to measure physically the shortest distance between the AC and the PSAF (AC-PSAF). The data were analysed statistically. The mean value and standard deviation were 20.7±4.2mm for AC-PAC and 20.7±4.3mm for AC-PSAF. The intraclass correlation coefficient between AC-PAC and AC-PSAF was 0.98. The CT-measured PAC locations were found to be almost identical to the PSAF positions identified physically in the samples. Preoperative CT localization of the PAC aids in avoiding injury to PSAA, while preoperative CT evaluation is important for each case due to significant individual variability in the anatomical PAC and PSAF locations.

Anatomic measurement of the depth and location of the sublingual fossa

The purpose of this study was to measure the depth and location of the sublingual fossa, a potential site of sublingual bleeding/lingual cortical perforation during endosseous implant placement in the mandibular interforaminal region (MIR), to clarify anatomical variation. Using the mandibles of 37 Japanese cadavers, the lingual depth (LD) between the lingual surface and the line perpendicular to the inferior margin of the mandible (IMM), as well as the vertical distance (VD) between the lingual surface and the IMM or the mental foramen (MF) level, were measured at defined points and lines within the MIR. The definite sublingual fossa (SF) was identified by the LD (≥ 1.0mm) and the VD, and the depth and location of the SF were determined. The depth ranged between 1.0mm and 5.8mm, and the vertical location ranged between 9.2mm and 15.7 mm from the IMM and between 2.2mm and 6.1mm from the MF level. These results revealed certain tendencies in the depth and location of the SF but the variation was substantial. The SF should be identified in each case as accurately as possible by CT before implant placement in the MIR to minimize the risk of the potential complications.

Fine structure of the human cochlear aqueduct: a light and transmission electron microscopic study of decalcified temporal bones

The morphologic features of the human cochlear aqueduct were examined using both light and electron microscopy. The lumen of the cochlear aqueduct was observed to be filled with dense, irregular connective tissue corresponding to dura mater. At the entrance to the cerebrospinal fluid space, the dense connective tissue in the ductal lumen was covered with a thin layer of a few flattened cells, which was contiguous with the arachnoid membrane of the brain. A simple low cuboidal epithelium also separated the perilymphatic space from the lumen of the duct. Our observations confirm the presence of a barrier membrane at the opening to the perilymphatic space, and suggest that no transport occurs in the human cochlear aqueduct.

Immunocytochemical studies of major gap junction proteins in rat salivary glands

We examined protein components of the gap junctions between acinar cells of the parotid, sublingual and submandibular glands of the rat, using type-specific antibodies directed against major gap junction proteins, connexin32 (Cx32) and connexin26 (Cx26). Double-immunofluorescence microscopy revealed that fluorescent spots of both connexins in the parotid and sublingual glands were distributed between the apposed regions of acinar cells. They appeared together, or were co-localized. The intensity of the Cx26-associated fluorescent signals was relatively weak in the submandibular glands compared with the other glands and was absent from some acini. When present, these spots were always co-localized with Cx32 immunoreactive positive spots. The results suggest that Cx32 and Cx26 in rat salivary glands are colocalized within the same gap junctional plaques when simultaneously expressed by the same acinar cells.

Deafness Due to Degeneration of Cochlear Neurons in Caspase-3-Deficient Mice

Mice that lack caspase-3, which functions in apoptosis, were generated by gene targeting and shown to undergo hearing loss. The ABR threshold of the caspase-3(-/-) mice was significantly elevated compared to that of caspase-3(+/+) mice at 15 days of age and was progressively elevated further by 30 days. Distortion product otoacoustic emissions were not detectable in caspase-3(-/-) mice at 15 days of age. Caspase-3(-/-) mice exhibited marked degeneration of spiral ganglion neurons and a loss of inner and outer hair cells in the cochlea at 30 days of age, although no such changes were apparent at 15 days. The degenerating neurons manifested features, including cytoplasmic vacuolization, distinct from those characteristic of apoptosis. Spiral ganglion neurons and cochlear hair cells thus appear to require caspase-3 for survival but not for initial development. The mapping of both the human caspase-3 gene and the locus responsible for an autosomal dominant, nonsyndromic form of hearing loss (DFNA24) to chromosome 4q35 suggests that the caspase-3(-/-) mice may represent a model of this human condition.

Differential expression of major gap junction proteins, connexins 26 and 32, in rat mammary glands during pregnancy and lactation

We examined the expression pattern of two major gap junction proteins, connexin 26 (Cx26) and connexin 32 (Cx32), in rat mammary glands during pregnancy and lactation. Immunohistochemically the two different Cxs were coexpressed in acinar cells and were independently modulated according to the physiological cell activity. Western blot analysis demonstrated that Cx26 gradually increased from early pregnancy, while Cx32 rapidly and dramatically increased at 16 h after parturition, and that both Cxs reached a maximum early in lactation. Increased expression of both Cxs was confirmed by Northern blot analysis showing that their mRNA transcripts were significantly induced on the day of parturition. We also analyzed double-immunofluorescent staining for Cx26 and Cx32 on a confocal laser scanning microscope, in order to examine colocalization of these Cxs in situ. Cx26 immunoreactivity mostly overlapped with Cx32-positive sites in acinar cells of lactating mammary glands, indicating that both Cxs were colocalized together in the same gap junctional plaques in lactation. These results suggest that upregulation of Cx26 and Cx32 in acinar cells at lactating stages, with colocalization in the same gap junctional plaques, may be important for control of secretion by acinar cells in rat mammary glands.

Heme oxygenase1 (HSP-32) is induced in myelin-phagocytosing Schwann cells of injured sciatic nerves in the rat

Schwann cells participate in myelin phagocytosis in the early stage of Wallerian degeneration, prior to the recruitment of macrophages. This is the first report that Schwann cells induce heme oxygenase-1 (HO-1), a 32-kDa heat shock protein, only when they have transformed into myelin-phagocytosing cells from myelinating cells (days 2-3) immediately after crush injury of rat sciatic nerves. Double immunofluorescent labelling for HO-1 and transferrin receptors revealed that HO-1-immunoreactive Schwann cells also expressed transferrin receptors suggesting activation of iron metabolism. The transient induction of HO-1 in Schwann cells may contribute to the adaptive function in an altered environment when the cells have lost contact with axons, and may play a crucial role in the ensuing regeneration.

An improved method for avulsion of lumbar nerve roots as an experimental model of nitric oxide-mediated neuronal degeneration

A root avulsion lesion on the spinal nerve of adult animals is a useful technique to make a model for axotomy-induced motoneuronal degeneration, which is thought to be mediated by nitric oxide (NO). Here, we show a simplified version of extravertebral avulsion in the young adult rat. The L4 nerve always runs under the transverse process of the L5 vertebra, which is located just rostral to the delineation of the iliac crest. We used the iliac crest as a clue for the identification of the L4 nerve during surgery, including before skin incision. In almost all animals the L4 nerve was successfully avulsed at the exit point from the spinal cord. This experimental result was similar to that shown in the previous literature; the number of either Nissl-stained or ChAT-immunoreactive (-ir) motoneurons (MN) gradually decreased, while NOS immunoreactivity was induced in the MN after avulsion. Furthermore, a combined method of confocal laser scanning microscopy and double fluorescent procedures carried out in this model suggested the existence of cellular interaction between NOS-ir MN and OX42-ir or ED1-ir microglia. It is concluded that this simple and fast method of spinal root avulsion is very useful for making a reproducible model of NO-mediated MN cell death, with which the mechanism of neuronal cell death, including neuron-glia interaction, can be further explored.

Changes in the distribution of peanut agglutinin (PNA) binding molecules during muscle reinnervation following nerve crush injury

Peanut agglutinin (PNA) staining during muscle reinnervation following a crushing injury of the sciatic nerve was performed in reference to the neural profiles immunolabeled with the PGP 9.5 antibody. PNA staining in the normal controls exhibited dots, granules, or lines along the length of the nerve fibers in the nerve trunk, but was faint or absent in the motor endplate. At seven days post-crush, PNA staining was detected around the vacuolated neural structures in the disorganized nerve trunk, but was still faint or absent in the motor endplate. At twenty-one days post-crush, when PGP 9.5-positive regenerating axons appeared in most of the motor endplates, PNA staining, either faint or strong, followed the pathway of the nerve fibers delineated by PGP 9.5-like immunoreactivity. During reinnervation to the motor endplates, PNA staining displayed signs of remodeling in the nerve trunk, such as marked variations in density and profile in the nerve fiber-associated dots or patches; it increased in intensity in the connective tissue covering the area of the motor endplate, as well as in the junctional myofiber surface. The structures recognizable by PNA coincided with components of the connective tissue such as collagen fibers and capillaries. Results suggest that: 1) the expression of PNA-binding molecules is dependent on the state of innervation, and 2) the spatiotemporal relationship between neural profiles and PNA staining provides sequences of axonal extension and subsequent nerve terminal maturation during regeneration in the motor endplate.

Involvement of PITPnm, a mammalian homologue of Drosophila rdgB, in phosphoinositide synthesis on Golgi membranes

Phosphatidylinositol transfer protein (PITP) is involved in phospholipase C-mediated signaling and membrane trafficking. We previously reported cloning and characterization of a gene encoding for membrane-bound PITP, named PITPnm, that is a mammalian homologue of the Drosophila retinal degeneration B (rdgB) gene (Aikawa, Y., Hara, H., and Watanabe, T. (1997) Biochem. Biophys. Res. Commun. 236, 559-564). Here we report the subcellular localization of PITPnm protein and provide evidence for its involvement in phosphatidylinositol 4-phosphate (PtdIns 4-P) synthesis. PITPnm is an integral membrane protein that largely localized in close association with membranes of Golgi vacuoles and the endoplasmic reticulum (ER). The amino terminus region of PITPnm was exposed to cytoplasmic side. Interaction with various phosphoinositides was observed in the amino terminus region spanning from 196 amino acids to 257 amino acids of PITPnm. At the amino terminus regions of 1-372 amino acids, PITPnm formed a complex with type III PtdIns 4-kinase. The transmembrane and carboxyl-terminal portions (residues 418-1242) functioned to retain the PITPnm in the Golgi vacuole. These results suggest that PITPnm plays a role in phosphoinositide synthesis on the Golgi vacuoles and possibly in the PtdIns signaling pathway in mammalian cells.

Induction of apoptosis in maxillary sinus cancer cells by 5-fluorouracil, vitamin A and radiation (FAR) therapy

The triple combination of 5-fluorouracil (5-FU), vitamin A and radiation (FAR therapy) has been used since 1972 to treat malignant tumors of the head and neck at Kyushu University. Using nick end labeling of tumor specimens, cells of human maxillary sinus carcinomas were observed previously to undergo apoptosis in response to FAR therapy. The present study evaluated the in vitro effects of FAR therapy on a human maxillary sinus cancer (IMC-4) cell line. We further compared the effects of FAR therapy on this cell line with those effects seen on tissue samples taken from patients with maxillary sinus cancers. DNA electrophoresis and electron microscopic examination of the IMC-4 cells after treatment with FAR therapy revealed typical apoptotic features. The effects of 50-100 micrograms/ml 5-FU, 10(-4) M all-trans-retinoic acid and radiation to 6 Gy on IMC-4 cells were evaluated by trypan blue dye exclusion and a cell colony formation assay. 5-FU and radiation caused direct cell death, while vitamin A mainly inhibited cell growth. The combination of these treatment as FAR therapy synergistically enhanced cell death and inhibited cell growth. Flow cytometry demonstrated that FAR-treated cells were arrested in the G1 phase of the cell cycle before undergoing apoptosis. To further investigate possible biological parameters influencing a tumor's apoptotic sensitivity, we also examined the expression of p53 in human maxillary sinus cancer cells and analyzed the relationship between p53 expression and apoptosis. However, no relationship was found between these two markers at the time point studied.

Three-dimensional structures of c-Kit-positive cellular networks in the guinea pig small intestine and colon

Cryosections and whole-mount preparations of the guinea pig small intestine and colon were single or double immunolabeled using the anti-c-Kit and protein gene product 9.5 antibodies. Immunolabeled specimens were observed under a confocal laser scanning microscope. The main findings of the present study are: (1) the distribution and profiles of three-dimensional structures of c-Kit-positive cellular networks in the small intestine and colon, and (2) the anatomical relations of c-Kit-positive cells to the enteric nerves in the layers. In the small intestine, c-Kit-positive cellular networks were observed at levels of the deep muscular plexus and myenteric plexus. The c-Kit-positive cellular networks ran along or overlay the nerve fibers at the deep muscular plexus, while they showed the reticular structures intermingled with the nerve elements at the myenteric plexus. In the colon, c-Kit-positive cellular networks were observed at levels of the submuscular plexus and myenteric plexus, and were further identified within the circular and longitudinal muscle layers as well as in the subserosal layer. In the circular muscle layer, c-Kit-positive cells surrounded the associated nerve fibers and extended several long processes toward the adjacent c-Kit-positive cells. The c-Kit-positive cellular networks within the longitudinal muscle layer as well as in the subserosal layer were not associated with the nerve fibers. In the layers of the intestinal wall with c-Kit-positive cells, the cellular networks of the interstitial cells were identified in ultrastructure. The characteristic profiles of c-Kit-positive cellular networks provide a morphological basis upon which to investigate the mechanisms regulating intestinal movement.

Specific localization of gap junction protein, connexin45, in the deep muscular plexus of dog and rat small intestine

Cellular networks of pacemaker activity in intestinal movements are still a matter of debate. Because gap-junctional intercellular communication in the intestinal wall may provide important clues for understanding regulatory mechanisms of intestinal movements, we have attempted to clarify the distribution patterns of three types of gap junction proteins. Using antibodies for connexin40, connexin43, connexin45, smooth muscle actin, and vimentin, immunocytochemical observations were made with the confocal laser scanning microscope on cryosections of fresh-frozen small intestine and colon of the dog and rat. Connexin 45 was localized along the deep muscular plexus of the small intestine in both dog and rat. Double labeling studies revealed that connexin45 overlapped with vimentin -, but not actin-positive areas, indicating the fibroblast-like nature of the cells, rather than their being smooth muscle-like. Connexin43 immunoreactivity appeared along the smooth muscle cell surface in the outer circular layer of the small intestine of both animals. Connexin 40 immunoreactivity was not observed in the muscle layer other than in the wall of large blood vessels. It is suggested that connexin45-expressing cells along the deep muscular plexus of dog and rat small intestine are likely to act as a constituent of a pacemaker system, which may include a conductive system, by forming a cellular network operating via specific types of gap junctions.

Expression of NOS, PSA-N-CAM and S100 protein in the granule cell migration pathway of the adult guinea pig forebrain

To investigate the possible role of nitric oxide (NO) in adult neurogenesis and neuron-glial migration in the rostral migratory stream (RMS), we used a double-labeled immunofluorescence technique together with confocal laser scanning microscopy, and examined the localization of nitric oxide synthase (NOS), the highly polysialylated isoform of neural cell adhesion molecule (PSA-N-CAM), and the astroglial marker in brain, S100 protein (S100), throughout the length of the subependymal layer (SEL) to olfactory bulb (OB) pathway of the adult guinea pig forebrain. Blast-like, beaded, clustered immature cellular elements stained for PSA-N-CAM and those having a typical astrocytic phenotypes positive for S100 protein were densely interlaced throughout the entire length of the SEL. Some S100 positive ependymoglial cells (tanycytes) gave off their basal projections into the closely packed PSA-N-CAM immunopositive clusters in the rostral extension of the subependymal zone (SEZre). The SEL was devoid of NOS immunoreactivity. A dense network of punctate, fenestrated and radially oriented immature cellular elements positive both for NOS and PSA-N-CAM intermingled and overlapped in the inner part of the internal granular layer (IGr), whereas in the outer part, PSA-N-CAM expression gradually diminished and the cells shifted to mature bipolar, spherical or spindle-shaped granule cells with uniform cellular contours, which were exclusively immunopositive for NOS. Radially oriented astroglial phenotypes were intertwined with PSA-N-CAM neuronal clusters in the SEL, and were closely apposed to NOS neuronal elements in the IGr. In summary, these results showed a distinct separation of neurons and glia as revealed by PSA-N-CAM and S100 protein immunostaining, and an inverse spatio-temporal correlation of expression between PSA-N-CAM (immature neuroblasts) and NOS (mature neurons) in the adult guinea pig RMS.

Changes in the phosphorylation states of connexin43 in myoepithelial cells of lactating rat mammary glands

Using specific antibodies and cDNA probe, we examined the expression pattern of a major gap junction protein, connexin43 (Cx43), in rat mammary glands during pregnancy and lactation. Double immuno-fluorescence revealed that the labeling of Cx43 was superimposed in the alpha-smooth muscle actin-positive cells, suggesting that myoepithelial cell were interconnected by gap junctions formed of Cx43. Just after delivery, the Cx43-labeled plaques were enlarged and increased in intensity. Northern and Western blot analyses confirmed the dramatic induction of Cx43 at both mRNA and protein levels on the day of parturition. Cx43 mRNA transcript immediately declined, while the increase of Cx43 protein continued for a few days. During pregnancy, immunoblots showed two bands of almost equal amounts at 43 and 45 kDa. Following delivery, the 45-kDa band gradually increased in intensity with a concomitant decrease of the 43-kDa band. From the sixth day of lactation, Cx43 was always detected as a single band at 45 kDa. Alkaline phosphatase treatment of immunoprecipitated Cx43 revealed that both bands represented phosphorylated forms, thus indicating that Cx43 was naturally phosphorylated and that it altered its phosphorylation states during lactation stages. These results suggest that the induction of Cx43 with the changes in the phosphorylation states plays an important role in the lactating function of myoepithelial cells in rat mammary glands. This is the first report on the changes of Cx43 phosphorylation states during physiological stages in vivo.

Dynamics of connexins, E-cadherin and alpha-catenin on cell membranes during gap junction formation

We examined the dynamics of connexins, E-cadherin and alpha-catenin during gap-junction disassembly and assembly in regeneration hepatocytes by immunofluorescence microscopy, and immunogold-electron microscopy using SDS-digested freeze-replicas. The present findings suggest that during the disappearance of gap junctions most of the gap junction plaques are broken up into smaller aggregates, and then the gap junction proteins may be removed from the cell membrane, but some of the connexons or connexins remain dispersed in the plane of membrane as pure morphologically indistinguishable intramembrane proteins. Double-immunogold electron microscopy using a polyclonal antibody for connexins and a monoclonal antibody for E-cadherin or alpha-catenin revealed co-localization of these molecules at cell-to-cell contact sites during the reappearance of gap junction plaques. This implies that, at least in regenerating hepatocytes, the cadherin-catenin complex-mediated cell-to-cell contact sites act as foci for gap junction formation. In addition, connexin-immunoreactivity was also observed along tight junctional strands, suggesting that the gap junction may also form along the tight junctions.

A single point mutation of hamster aminoacyl-tRNA synthetase causes apoptosis by deprivation of cognate amino acid residue

BACKGROUND

We have isolated a series of temperature-sensitive mutants for cell-proliferation from the BHK21 cell line derived from the golden hamster (Nishimoto & Basilico 1978; Nishimoto et al. 1982). Using these mutants as a recipient of DNA-mediated gene transfer, we have been cloning human genes which complement these ts mutants.

RESULTS

Cultures of tsBN269 cells, a temperature-sensitive mutant of the BHK21 cell line, underwent apoptosis at 39.5 degrees C, a nonpermissive temperature. The gene complementing the tsBN269 cells was cloned and found to encode lysyl-tRNA synthetase. Indeed, tsBN269 cells were found to have a single cytosine to a thymine point mutation at the first nucleotide of codon 542 in hamster lysyl-tRNA synthetases. Due to this mutation, the activity of lysyl-tRNA synthetase was reduced--even at 33.5 degrees C, a permissive temperature. Consistent with these findings, while supplementation with lysine permitted tsBN269 cells to grow at a nonpermissive temperature, the deprivation of lysine caused apoptosis in tsBN269 cells, even at 33.5 degrees C. Cycloheximide inhibited the apoptosis caused by lysine starvation at 33.5 degrees C, but not at 39.5 degrees C. We also found that another hamster temperature-sensitive mutant, tsBN250, which is defective in histidyl-tRNA synthetase, entered apoptosis with the deprivation of histidine.

CONCLUSION

Our data suggested that the defect in aminoacyl-tRNA synthetase turned on the cascade of apoptosis that was already present in the cells.

Connexin 43 and the glucose transporter, GLUT1, in the ciliary body of the rat

To investigate the relationship between the gap junction protein connexin 43 and the glucose transporter GLUT1, their localization was visualized by double-immunofluorescence microscopy using frozen sections as well as immunogold staining of ultrathin frozen sections. In pigmented epithelial cells, most of the GLUT1 was localized along the plasma membrane facing the blood vessels, whereas in non-pigmented epithelial cells, it was present along the plasma membrane facing the aqueous humor. Connexin 43 was abundant in the ciliary body and localized mainly in the gap junctions connecting the pigmented and non-pigmented epithelial cells. Localization of GLUT1 and connexin 43 in the blood-aqueous barrier suggests that GLUT1, connexin 43, and GLUT1 disposed in this order could be a machinery responsible for the transport of glucose across the blood-aqueous barrier.

Immunolocalization of GLUT1 and connexin 26 in the rat placenta

Interhemal membrane in the rat placenta is composed of three trophoblastic layers and endothelial cells. GLUT1, an isoform of the facilitated-diffusion glucose transporter, is abundant in the cells of the placental barrier, i.e., syncytiotrophoblastic layers I and II. GLUT1 is localized at the plasma membranes of the maternal-blood side of syncytiotrophoblastic layer I, and of the fetal-blood side of syncytiotrophoblastic layer II. Double-immunofluorescence microscopy has shown that connexin 26 is present between these GLUT1-positive sites, i.e., between syncytiotrophoblastic layers I and II. Immunogold electron microscopy has revealed that connexin 26 is localized in the gap junctions connecting the two layers. Connexin 26 in these layers therefore makes them functionally a single syncytial layer for the transfer of small molecules such as glucose in the rat placental barrier. These results suggest that glucose transfer in the rat placental barrier is carried out as follows: GLUT1 is used for the entry of glucose into the cytoplasm of syncytiotrophoblastic layer I, connexin 26 for the transfer of glucose from syncytiotrophoblastic layer I to syncytiotrophoblastic layer II, and GLUT1 for the exit of glucose to the fetal circulation.

Colocalization of connexin 43 and connexin 45 but absence of connexin 40 in granulosa cell gap junctions of rat ovary

The expression and localization of gap junction family proteins (connexins) were examined in nonstimulated and gonadotrophin-stimulated ovarian follicles of immature rats. Immunoblot and RNA blot analysis showed the presence of connexin (Cx) 43, Cx40 and Cx45 in ovarian tissue. Of these connexin proteins, Cx43 and Cx45 were identified by immunofluorescent microscopy between granulosa cells in characteristic expression patterns related to follicular developmental stages, while Cx40 was not expressed in granulosa cells but was detected in blood vessels in ovarian stroma. In some plaques of gap junction between granulosa cells, Cx45 was found to be colocalized with Cx43. In immunofluorescent microscopy, the expression of Cx43 was increased with follicular growth, but decreased after induction of ovulation by injection of human chorionic gonadotrophin. In contrast, the Cx45 protein was constantly expressed through follicular development; however, after ovulation, no staining of Cx45 was detected in the corpus luteum. Dual expression and the functional role of Cx43 and Cx45 in cell-to-cell communication in ovarian granulosa cells at various developmental stages were discussed.

Apoptosis is induced in BHK cells by the tsBN462/13 mutation in the CCG1/TAFII250 subunit of the TFIID basal transcription factor

A temperature-sensitive (ts) mutant of the BHK21 cell line derived from golden hamsters, tsBN462 has a mutation in the gene encoding the largest subunit of the TFIID complex, TAFII250/p230/CCG1, and arrests in the G1 phase at the nonpermissive temperature, 39.5 degrees C. We found that tsBN462 cells underwent apoptosis following growth arrest at 39.5 degrees C, suggesting a role for CCG1 as a repressor of apoptosis. By electron microscopic observation, tsBN462 cells at 39.5 degrees C showed characteristic features of apoptosis. Apoptosis was not suppressed by expression of Bc1-2 or the adenovirus E1B 19 kDa protein. Cell death was suppressed completely by expression of wild-type CCG1 and partially by wild-type p53, a growth suppressor protein. Cell cycle arrest induced by p53 may help survival of tsBN462 cells at 39.5 degrees C. Apoptosis was accelerated in SV40 large T antigen-transformed tsBN462 cells at 39.5 degrees C where SV40 large T antigen formed a complex with p53, implying that the apoptosis of tsBN462 cells at 39.5 degrees C occurred in a p53-independent manner. Our results suggest that CCG1/TAFII250 is required for the expression of factors regulating apoptosis.

Expression of tissue-type plasminogen activator and its inhibitor couples with development of capillary network by human microvascular endothelial cells on Matrigel

Human omental microvascular endothelial (HOME) cells seeded on Matrigel begin to migrate within 1 h, forming honeycomb-like structures and capillary-like networks within 18 h. Cross-sections of the capillary networks show them to be tube-like structures. Northern blot analysis showed that tissue-type plasminogen activator (t-PA) mRNA synthesis increased from the initial state at 0 h after seeding on Matrigel, reaching a steady state after 4 h. This elevated cellular t-PA mRNA level decreased markedly at 24 h. In contrast, the cellular plasminogen activator inhibitor-1 (PAI-1) mRNA level demonstrated biphasic curves during the 24 h after seeding on Matrigel: the PAI-1 mRNA level was increased eightfold initially at 4 h over that at 0 h, then declined, and again secondarily increased to greater than tenfold at 18 h. Cellular levels of both 72 kD type IV collagenase and tissue inhibitor of metalloproteinase (TIMP-2) mRNA were increased only a slightly within 2-4 h. These elevated mRNA levels were maintained for 18 h, while the TIMP-1 mRNA level increased up to 18 h, reaching around three times the level at 0 h. However, on collagen-coated dishes, cellular levels of t-PA, PAI-1, 72 kD type IV collagenase, TIMP-1, and TIMP-2 mRNA were not greatly changed during incubation for 24 h. On Matrigel, the cellular t-PA mRNA level at 18 h after seeding was greatly increased when treated with specific anti-transforming growth factor-beta (TGF-beta) antibody. In contrast, both PAI-1 and TIMP-1 mRNA levels at 18 h were reduced in the presence of anti-TGF-beta antibody. Development of the capillary network on Matrigel was inhibited in the presence of anti-t-PA antibody. Epidermal growth factor (EGF) enhanced t-PA gene expression and TGF-beta inhibited its expression in HOME cells cultured on collagen-coated dishes. On the other hand, TGF-beta enhanced cellular expression of the PAI-1 gene. The formation of a capillary network by HOME cells on Matrigel appears to be balanced by angiogenic EGF and anti-angiogenic TGF-beta through modulation of PA activity.

Molecular cloning of a human cDNA encoding a novel protein, DAD1, whose defect causes apoptotic cell death in hamster BHK21 cells

The tsBN7 cell line, one of the mutant lines temperature sensitive for growth which have been isolated from the BHK21 cell line, was found to die by apoptosis following a shift to the nonpermissive temperature. The induced apoptosis was inhibited by a protein synthesis inhibitor, cycloheximide, but not by the bcl-2-encoded protein. By DNA-mediated gene transfer, we cloned a cDNA that complements the tsBN7 mutation. It encodes a novel hydrophobic protein, designated DAD1, which is well conserved (100% identical amino acids between humans and hamsters). By comparing the base sequences of the parental BHK21 and tsBN7 DAD1 cDNAs, we found that the DAD1-encoding gene is mutated in tsBN7 cells. The DAD1 protein disappeared in tsBN7 cells following a shift to the nonpermissive temperature, suggesting that loss of the DAD1 protein triggers apoptosis.

Localization of gap junction proteins, connexins 32 and 26, in rat and guinea pig liver as revealed by quick-freeze, deep-etch immunoelectron microscopy

By use of site-specific antibodies against synthetic oligopeptides, we examined the localizations of the gap junction proteins connexin 32 (Cx32) and connexin 26 (Cx26) in rat and guinea pig liver. Double-labeling immunofluorescence microscopy revealed that in guinea pig liver both proteins were spread throughout the liver lobules and seemed to localize together within the same gap junction plaque. In rat liver, co-localization of both Cx32 and Cx26 in the same plaques was also suggested in periportal zones. Quick-freeze, deep-etch immunoelectron microscopy showed that immunolabeling of isolated guinea pig liver gap junction plaques with either Cx32 or Cx26 antiserum yielded complete and dense antibody decoration of the cytoplasmic surface of the plaques. In isolated rat liver plaques, the cytoplasmic surfaces were densely decorated with Cx32 antiserum, whereas Cx26 labeling yielded diffuse decoration with variable intensity of the plaques. In both species we did not observe any focal or patchy clusters of the labeling in any plaques examined. Double-labeling immunoelectron microscopy confirmed that both Cx32 and Cx26 are co-localized in the same gap junction plaques. These results suggest that in hepatocytes expressing both Cx32 and Cx26, both types of gap junction proteins are not segregated but intermingle randomly within the same plaques.

Cytoplasmic surface ultrastructures of gap junctions in bovine lens fibers

PURPOSE

To examine the cytoplasmic surface ultrastructures of lens fiber gap junctions, where the cytoplasmic domains of connexons were expected to be exposed.

METHODS

Bovine lens fiber gap junctions, both in situ and in the form of isolated membranes, were examined with the deep etching replica methods. Isolated membranes were also examined with the same methods after the treatment with endoproteinase glu-C, which is known to cleave off the cytoplasmic domain of a putative lens fiber connexin MP70 to determine whether any structural changes should occur between proteolyzed and nonproteolyzed gap junctions. In addition, both proteolyzed and nonproteolyzed gap junctions were studied by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunolabeling with the monoclonal antibody that recognized cytoplasmic domain of MP70 to clarify whether MP70 lost its cytoplasmic domain by the treatment with endoproteinase glu-C.

RESULTS

Gap junctions were shown to have particulate substructures on their cytoplasmic surfaces; the distributions of the particles were restricted within gap junctional plaques and the non-gap-junctional areas showed smooth cytoplasmic surfaces. Although the treatment with endoproteinase glu-C failed to remove the cytoplasmic particles of gap junctions in deep etching replica study, MP70 was shown to have lost its cytoplasmic domain in sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunolabeling studies.

CONCLUSIONS

Each particle revealed on the cytoplasmic surfaces of lens fiber gap junctions corresponded to the cytoplasmic domain of a connexon. The particles were not removed by the treatment with endoproteinase glu-C, whereas MP70 was cleaved by the same treatment.

Rapid freezing replica studies of membrane specializations in the proximal tubules of mouse kidney

The membrane specializations of the fresh unfixed kidney cortex of adult and neonatal ICR mice were examined by using rapid freezing replica methods. In proximal tubular cells, numerous apical intracellular tubules exhibited helical patterns on the E face with a pitch of about 12 nm. This regular pattern was often continuous with similar striped indentations on the edge of the vacuoles connecting with the tubules. On the luminal surface (ES) of these vacuoles, membrane surface particles were arranged regularly in striped patterns with a center-to-center spacing of about 12 nm. We could not identify differentiations on the PF or PS of the same membrane systems. Another membrane specialization was a plaque or patch of clear pits in tilted lattice alignments on the P face of the large vacuoles with a center-to-center spacing of about 20 nm. This type of specialization was often observed in the neonatal mice proximal tubular cells. These membrane specializations may indicate the active membrane functions in the proximal tubules and suggest the functional continuity and structural relationship of these apical endocytic membrane systems.

Ultrastructure of the guinea pig cochlear aqueduct. An electron microscopic study of decalcified temporal bones

The ultrastructure of the guinea pig cochlear aqueduct was examined using semi-thin and thin sections. The lumen of the cochlear aqueduct was occupied by a sparse meshwork of fibroblasts and delicate connective tissue trabeculae. The periotic tissue lining the bony wall of the aqueduct was composed of multiple layers of both elongated cells and densely arranged laminae of collagen fibrils. These structures were identical to those of the dura mater and the arachnoid. The opening to the perilymphatic space of the scala tympani also contained connective tissue trabeculae, but the arrangement of fibroblasts was more compact here than in the main part of the duct. These structural features suggest that fluid can move freely through cochlear aqueduct, and that the effects of sudden pressure changes in the CSF may be protected against by the densely and perpendicularly arranged fibroblast at the opening to the perilymphatic space.

Computer-aided three-dimensional reconstruction of guinea pig cochlear aqueduct

A computer-aided method of three-dimensional reconstruction was applied to the determination of the overall spatial configuration of the guinea pig cochlear aqueduct. The rotation function of the reconstructed images was useful in showing the individual small parts of the duct. A semi-translucent display of the segmental reconstruction of the duct demonstrated a difference in the density of the cellular components between the opening to the perilymphatic space and the duct portion. We propose that the cochlear aqueduct serves as a protective mechanism against a sudden change in CSF pressure in the subarachnoid space.

Quick-freeze, deep-etch visualization of the 'cytoskeletal spring' of cochlear outer hair cells

The lateral membrane system of the cochlear outer hair cell, consisting of the lateral plasma membrane, pillars, filamentous lattice and subsurface cisternae, is considered to be involved in the contractile movement of the isolated cochlear outer hair cell. The filamentous lattice, called the cytoskeletal spring, has been identified in the demembranated cochlear outer hair cell treated with the detergent Triton X-100. In this study, the quick-freeze, deep-etch method was applied to demonstrate the three-dimensional organization of both the filamentous and membranous structures of the lateral membrane system of cochlear outer hair cells. Treatment with saponin revealed that the inner leaflet of the lateral plasma membrane of the cochlear outer hair cell possesses more membrane particles than the outer leaflets, and that the pillars are closely associated with membrane particles in the inner leaflet of the lateral membrane. The presence of filamentous bridges between the filamentous lattice and the subsurface cisternae was also detected. We propose that the lateral membrane system in the cochlear outer hair cell may play an important role in the tuning mechanisms within the cochlea in normal hearing.