Kazutoshi Unno

Chloroplast development in Arabidopsis thaliana requires the nuclear-encoded transcription factor Sigma B

Development of plastids into chloroplasts, the organelles of photosynthesis, is triggered by light. However, little is known of the factors involved in the complex coordination of light‐induced plastid gene expression, which must be directed by both nuclear and plastid genomes. We have isolated an Arabidopsis mutant, abc1, with impaired chloroplast development, which results in a pale green leaf phenotype. The mutated nuclear gene encodes a sigma factor, SigB, presumably for the eubacterial‐like plastid RNA polymerase. Our results provide direct evidence that a nuclear‐derived prokaryotic‐like SigB protein, plays a critical role in the coordination of the two genomes for chloroplast development.

Parachordoma with multiple metastases.

We present a very rare case of parachordoma with local aggressiveness and widespread metastases. A 68-year-old male presented with a mass in his left calf. The lesion was depicted as a poorly marginated mass with inhomogeneous signal intensity on magnetic resonance imaging. The tumor invaded surrounding muscles, neurovascular bundles, and bones. Widespread metastasis to lung, bone, and skin developed after amputation surgery. The histologic features of primary and metastatic lesions were the same and consistent with parachordoma.

Viral Behavior of Paracrystalline Inclusions in Osteoclasts of Paget's Disease of Bone

Fresh tissues from six patients with Pagets disease of bone were examined ultrastructurally to investigate whether the characteristic paracrystalline inclusions in pagetic osteoclasts revealed viral behavior. These inclusions appeared as microfilamentous aggregates in both nuclei and cytoplasm of the osteoclasts in all six cases. The filamentous elements of the inclusions with a diameter of 11-15 nm showed tubular structures with a central electron-lucent zone measuring 5-7 nm in diameter. Viral budding-like structures containing these inclusions were found at the peripheral cytoplasm or cell processes in the ruffled border of some pagetic osteoclasts in two cases. The inclusions in the budding-like structures were often arrayed in a parallel fashion on the cytoplasmic side of the cell membranes of extruded cytoplasm or cell processes. Virion-like particles were also found in the extracellular spaces of the ruffled border. Marked nuclear degeneration was often seen in pagetic osteoclasts of three cases, although other nuclei in the same osteoclasts appeared normal. The degenerated nuclei showed nuclear ring formation where destroyed nuclear membranes were seen and disappearance of nuclear matrices was noted. Since the modifications were always associated with the accumulation of abundant inclusions, they were probably caused by the inclusions. These findings suggested that the inclusions showed viral behavior in pagetic osteoclasts, and that the nuclear modifications were caused by virus infection.

RT-PCR Suggests Human Skeletal Muscle Origin of Alveolar Soft-Part Sarcoma

In 1952, Christopherson et al. proposed that alveolar soft-part sarcoma (ASPS) was a distinct entity with unique clinical and pathological features. Since their report, its histogenesis has not been determined. In order to clarify the histogenesis of ASPS, a study using reverse transcription polymerase chain reaction using cDNAs from MyoD1 and myogenin, and the actin filament from human-skeletal-muscle-related mRNAs has been performed in 5 cases of ASPS. The expression of MyoD1 and myogenin was determined in 5 and 2 cases of the 5 cases, respectively. Moreover, expression of the many mRNAs from the actin filament of skeletal muscle was also found in ASPS. According to these findings, it is now postulated that ASPS is of skeletal muscle origin.

Morphogenesis and origin of fibrous long-spacing collagen fibers in collagenase-treated mouse skin tissues

Morphogenesis and origin of fibrous long-spacing collagen (FLS) fibers in newborn mouse skin tissues treated with collagenase were examined using ultrastructural observation, morphometry, histochemical methods, and immunoelectron microscopy. The enzyme caused both the partial destruction of basal laminae and the formation of abundant FLS fibers in the dermal matrix. The fibers were usually distributed in the vicinity of basal laminae in the capillaries or basal layer cells. The fibers were characterized by the cross-striated dark bands with about 91 nm periodicity and longitudinally aligned filaments with a diameter of about 6.5 nm. The dark bands of FLS fibers were often continuous with the basal laminae. Histochemical results showed that the dark bands contained the similar mucopolysaccharides which were involved in the basal laminae. Immunoelectron microscopic results showed that laminin was present in the dark bands as well as in the basal laminae, and that type VI collagen was located in the filaments of FLS fibers. These results suggest that the dark bands are formed by products similar to basal laminae and that the products were precipitated on type VI collagen-contained filaments with periodic intervals of about 91 nm. Morphometric examination revealed that there was no differences in ultrastructure between FLS fibers of a collagenase-treated mouse and those of a human neural tumor.

β-1,3-D-Glucan Transported from Golgi Apparatus of Japanese Pear Leaves is a Component of Extracellular Polysaccharides Accumulated after AK-toxin I Treatment

This fluorescence and immunoelectron microscopic study showed that β-1,3-D-glucan accumulated only in leaves of a susceptible cultivar of Japanese pear after treatment with a host-specific toxin, AK-toxin I, from Alternate, alternata Japanese pear pathotype. The positive fluorescent reaction of callose was detected only in aniline blue fluorochrome-stained sections from toxin-treated leaves of the susceptible cultivar: positive sites were observed on cell walls of leaf cells. The sites of callose deposition were probably consistent spatially with modified sites on the plasma membrane that were observed only in the toxin-treated leaves of the susceptible cultivar. The toxin-induced modifications, identified as damage to the plasma membrane, were characterized by invagination of the plasmalemma specifically at plasmodesmata and as the concomitant accumulation of extracellular polysaccharides at the invaginated sites. A positive reaction to anti-β-1,3-D-glucan antibody was detected at the polysaccharides, Golgi vesicles, and trans-Golgi network (TGN) of toxin-treated leaves of the susceptible cultivar, but not at Golgi vesicles and TGN of water-treated ones. The cis-, medial and trans-Golgi stacks of toxin-treated leaves of the susceptible cultivar were negative for the antibody. The results showed that the polysaccharides, Golgi vesicles and TGN contained abundant β-1,3-D-glucan and that the glucan was transported from the Golgi apparatus via Golgi vesicles to the modified sites in cells of toxin-treated leaves of the susceptible cultivar.

Smooth Tubular Aggregates Associated with Plasmalemmal Invagination in Alveolar Soft Part Sarcoma

The ultrastructure of four alveolar soft part sarcomas was examined to search for ultrastructural signs of myogenic or neural origin. A new ultrastructural structure, an unusual tubular structure, was found in two of four cases. The structure appeared as a large, smooth, tubular aggregate in the cytoplasm of some tumor cells but did not show a honeycomb arrangement of tubules. The aggregate was composed of long, serpentine, branching, smooth, irregularly arranged tubules without ribosomes that ran in various directions. The aggregates intermingled with small amounts of cytoplasmic organelles. Because the aggregated tubules were at times continuous with cell membranes, it was shown that they were the complex extensions or invaginations of cell membranes. Neither myelin-axon complexes nor myofilaments, including Z band material, were seen in any case. There was a possibility that the smooth tubular aggregate was a T-tubule-like structure, suggesting that the tumors were derived from skeletal muscle cells.

Overexpression of the protein disulfide isomerase AtCYO1 in chloroplasts slows dark-induced senescence in Arabidopsis

BackgroundChlorophyll breakdown is the most obvious sign of leaf senescence. The chlorophyll catabolism pathway and the associated proteins/genes have been identified in considerable detail by genetic approaches combined with stay-green phenotyping. Arabidopsis CYO1 (AtCYO1), a protein disulfide reductase/isomerase localized in the thylakoid membrane, is hypothesized to assemble the photosystem by interacting with cysteine residues of the subunits.ResultsIn this study, we report that ectopic overexpression of AtCYO1 in leaves induces a stay-green phenotype during darkness, where oxidative conditions favor catabolism. In AtCYO1ox leaves, Fv/Fm and both chlorophyll a and chlorophyll b content remained high during dark-induced senescence. The thylakoid ultrastructure was preserved for a longer time in AtCYO1ox leaves than in wild type leaves. AtCYO1ox leaves maintained thylakoid chlorophyll-binding proteins associated with both PSII (D1, D2, CP43, CP47, LHCB2, and Cyt f) and PSI (PSA-A/B), as well as stromal proteins (Rubisco and ferredoxin-NADP+ reductase). AtCYO1ox did not affect senescence-inducible gene expression for chlorophyll catabolism or accumulation of chlorophyll catabolites.ConclusionsOur results suggest that ectopic overexpression of AtCYO1 had a negative impact on the initiation of chlorophyll degradation and proteolysis within chloroplasts. Our findings cast new light on the redox regulation of protein disulfide bonds for the maintenance of functional chloroplasts.