Intralobular Distribution of Vitamin A-Storing Lipid Droplets in Hepatic Stellate Cells with Special Reference to Polar Bear and Arctic Fox

We examined the liver of adult polar bears, arctic foxes, and rats by gold chloride staining, fluorescence microscopy for the detection of autofluorescence of vitamin A, hematoxylin-eosin staining, staining with Masson's trichrome, Ishii and Ishii's silver impregnation, and transmission electron microscopical morphometry. The liver lobules of the arctic animals showed a zonal gradient in the storage of vitamin A. The density (i.e., cell number per area) of hepatic stellate cells was essentially the same among the zones. These results indicate that the hepatic stellate cells of the polar bears and arctic foxes possess heterogeneity of vitamin A-storing capacity in their liver lobules

Mitochondrial Abnormality Facilitates Cyst Formation in Autosomal Dominant Polycystic Kidney Disease

ABSTRACT Autosomal dominant polycystic kidney disease (ADPKD) constitutes the most inherited kidney disease. Mutations in the PKD1 and PKD2 genes, encoding the polycystin 1 and polycystin 2 Ca2+ ion channels, respectively, result in tubular epithelial cell-derived renal cysts. Recent clinical studies demonstrate oxidative stress to be present early in ADPKD. Mitochondria comprise the primary reactive oxygen species source and also their main effector target; however, the pathophysiological role of mitochondria in ADPKD remains uncharacterized. To clarify this function, we examined the mitochondria of cyst-lining cells in ADPKD model mice (Ksp-Cre PKD1flox/flox) and rats (Han:SPRD Cy/+), demonstrating obvious tubular cell morphological abnormalities. Notably, the mitochondrial DNA copy number and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) expression were decreased in ADPKD model animal kidneys, with PGC-1α expression inversely correlated with oxidative stress levels. Consistent with these findings, human ADPKD cyst-derived cells with heterozygous and homozygous PKD1 mutation exhibited morphological and functional abnormalities, including increased mitochondrial superoxide. Furthermore, PGC-1α expression was suppressed by decreased intracellular Ca2+ levels via calcineurin, p38 mitogen-activated protein kinase (MAPK), and nitric oxide synthase deactivation. Moreover, the mitochondrion-specific antioxidant MitoQuinone (MitoQ) reduced intracellular superoxide and inhibited cyst epithelial cell proliferation through extracellular signal-related kinase/MAPK inactivation. Collectively, these results indicate that mitochondrial abnormalities facilitate cyst formation in ADPKD

Conflict Over Control in the Legume-Rhizobia Symbiosis

Microbes can dramatically alter the fitness of host organisms, ranging in effect from mutualistic to antagonistic. Across this spectrum of fitness effects the microbial symbiont is predicted to optimize its own fitness benefits either through positive feedback (i.e., mutualism) or exploitation (i.e., antagonism). The legume-rhizobium symbiosis has emerged as a powerful system to study the control mechanisms of hosts and the corresponding subversion of control by symbionts. Rhizobial bacteria are housed in legume root nodules where they provide the costly services of nitrogen fixation in return for host derived carbon. However, variation in symbiont quality and lifestyle strategies can result in fitness conflict between host and symbiont. I used the symbiosis between Lotus japonicus and Mesorhizobium loti to investigate host control over symbionts across the mutualism-antagonism spectrum. For chapter 1 I investigated the effects of host control on symbiont fitness when symbionts vary in their fitness effects. I found that the L. japonicus host can adaptively alter the fitness of symbionts dependent on symbiotic nitrogen fixation. For chapter 2 I examined how varying host investment into symbiosis affects the fitness of hosts and symbionts. I found host control was maintained when host investment into symbiosis was altered. However, at high levels of host investment in symbiosis with a high-quality symbiont I uncovered evidence that host fitness is optimized, while symbiont fitness continues to increase. For chapter 3 I tested the effects of host control and varying levels of host investment on the evolution of symbiont services to hosts. After experimentally evolving rhizobial symbionts of mediocre quality in multiple experiments, the phenotypic data was most consistent with a shift towards antagonistic phenotypes. Together, these results highlight the intense conflict over resources that can lead to the destabilization or breakdown of the mutualism between legumes and rhizobia

Conflict Over Control in the Legume-Rhizobia Symbiosis

Microbes can dramatically alter the fitness of host organisms, ranging in effect from mutualistic to antagonistic. Across this spectrum of fitness effects the microbial symbiont is predicted to optimize its own fitness benefits either through positive feedback (i.e., mutualism) or exploitation (i.e., antagonism). The legume-rhizobium symbiosis has emerged as a powerful system to study the control mechanisms of hosts and the corresponding subversion of control by symbionts. Rhizobial bacteria are housed in legume root nodules where they provide the costly services of nitrogen fixation in return for host derived carbon. However, variation in symbiont quality and lifestyle strategies can result in fitness conflict between host and symbiont. I used the symbiosis between Lotus japonicus and Mesorhizobium loti to investigate host control over symbionts across the mutualism-antagonism spectrum. For chapter 1 I investigated the effects of host control on symbiont fitness when symbionts vary in their fitness effects. I found that the L. japonicus host can adaptively alter the fitness of symbionts dependent on symbiotic nitrogen fixation. For chapter 2 I examined how varying host investment into symbiosis affects the fitness of hosts and symbionts. I found host control was maintained when host investment into symbiosis was altered. However, at high levels of host investment in symbiosis with a high-quality symbiont I uncovered evidence that host fitness is optimized, while symbiont fitness continues to increase. For chapter 3 I tested the effects of host control and varying levels of host investment on the evolution of symbiont services to hosts. After experimentally evolving rhizobial symbionts of mediocre quality in multiple experiments, the phenotypic data was most consistent with a shift towards antagonistic phenotypes. Together, these results highlight the intense conflict over resources that can lead to the destabilization or breakdown of the mutualism between legumes and rhizobia

CHARACTERISTIC DISTRIBUTION DENSITY OF ORGANELLES IN THE CYTOPLASM OF RESPECTIVE KINDS OF CELL LINEAGES OF ASCIDIAN EMBRYOS

In the early embryos of the ascidian (Halocynthia roretzi), regional cytoplasmic differences arise just after fertilization.We successively studied the characteristic features of the cytoplasm of those regions in the embryonic cells during the entire ontogenic process from the unfertilized egg to the tadpole larva.The embryos and larvae were fixed in a mixture of osmium and glutaraldehyde, and the distribution of the organelles in the entire cytoplasm was observed with light and electron microscopy. According to the analysis of the distribution density of the organelles which occupied a given area of the cytoplasm on the section, we introduced the “organelle region” in the cytoplasm and further calculated the approximate area ratios of the “organelle regions” in the cytoplasm of each cell lineage.As a result, it was demonstrated that the characteristic distribution mode was already present in the cytoplasm of the cell lineages of the 8-cell-stage embryos. The features of the cytoplasm in each embryonic cell lineage, moreover, reflected those of the corresponding larval tissue.Our results not only demonstrate that the structural tissue specificity is expressed at an extremely early stage during the ascidian embryogenesis but also suggest that the corresponding functional differentiation among the cell lineages occurs early

ULTRASTRUCTURAL FEATURES OF THE CYTOPLASM OF RESPECTIVE KINDS OF CELL LINEAGES OF CLEAVAGE-ARRESTED ASCIDIAN EMBRYO

We observed the ultrastructual features of the cytoplasm in the cell lineages of the cleavage-arrested embryos of the ascidian, Halocynthia roretzi, and compared them with those of the cytoplasm in the corresponding cell lineages of the normal embryos or in the corresponding tissues of the normal larva, in order to examine the presence or the degree of the cellular differentiation without the cleavage.The cleavage of the embryos was arrested by the cytochalasin B at the 16-cell stage and the embryos were cultured in sea water containing cytochalasin B until the developmental time equivalent to the hatching of the control larva.As a result, the cytoplasmic components in the cleavage-arrested 16-cell embryos resembled those observed in the corresponding tissues of the normal larvae, especially in the b5.3 and b5.4 blastomers (epidermal lineage cells) and in the B5.1 blastomeres (which give rise to the endodermal, mesenchymal and muscle cells) but they were less uniforml y organized and their polarity or orientation was very random and irregular, compared with those in the normal larvae.These results demonstrated that the morphological differentiation similar to the larval tissue differentiation could proceed even in the cleavage-arrested embryos to a certain extent