Effects of Habitat Connectivity on the Abundance and Species Richness of Coral Reef Fishes: Comparison of an Experimental Habitat Established at a Rocky Reef Flat and at a Sandy Sea Bottom

Coral reef fish assemblages are widely recognized for the coexistence of numerous species, which are likely governed by both coral diversity and substratum complexity. However, since coral reefs provide diverse habitats due to their physical structure and different spatial arrangements of coral, findings obtained from an isolated habitat cannot necessarily be applied to fish assemblages in other habitats (e.g. continuous habitats). The aim of this study, therefore, was to determine by a field experiment whether habitat connectivity (spatial arrangement of coral colonies) affects abundance and species richness of fishes in an Okinawan coral reef. The experiment consisted of transplanted branching coral colonies at a 4m×8m quadrat at both a rocky reef flat and sandy sea bottom. Generally, the abundance of fishes was greater at the sandy sea bottom, especially for three species of pomacentrids, one species of labrids, one species of chaetodontids and two species of apogonids. Species–area curves showed that the species richness of fishes was significantly greater in the quadrat at the sandy sea bottom at 3, 6 and 9 months after the start of the experiment. The rate of increase in abundance of fishes per area was significantly greater in the quadrat at the sandy sea bottom over the study period. The results of rarefaction analyses showed that the rate of increase in species richness per abundance was significantly higher in the quadrat at the sandy sea bottom in the juvenile settlement period, indicating that the magnitude of dominance by particular species was greater at the sandy sea bottom habitat. Our findings suggest that habitat connectivity affects the abundance and species richness of coral reef fishes, i.e. the isolated habitat was significantly more attractive for fishes than was the continuous habitat. Our findings also suggest that the main ecological factors responsible for organization of fish assemblage at a continuous habitat and at an isolated habitat are different.     

Molecular dissection of egg fertilization signaling with the aid of tyrosine kinase-specific inhibitor and activator strategies

Fertilization is triggered by sperm-egg interaction and fusion that initiate a transient rise(s) in the free intracellular calcium ([Ca(2+)](i)) that is responsible for a series of biochemical and cell biological events, so-called "egg activation". Calcium-dependent egg activation leads to the initiation of developmental program that culminates in the birth of individuals. A growing body of knowledge has uncovered the molecular mechanisms underlying sperm-induced transient [Ca(2+)](i) increase(s) to some extent; namely, in most animals so far studied, a second messenger inositol 1,4,5-trisphosphate (IP(3)) seems to play a pivotal role in inducing [Ca(2+)](i) transient(s) at fertilization. However, signaling mechanisms used by sperm to initiate IP(3)-[Ca(2+)](i) transient pathway have not been elucidated. To approach this problem, we have employed African clawed frog, Xenopus laevis, as a model animal and conducted experiments designed specifically to determine the role of the Src family protein-tyrosine kinases (SFKs or Src family PTKs) in the sperm-induced egg activation. This review compiles information about the use of PTK-specific inhibitors and activators for analyzing signal transduction events in egg fertilization. Specifically, we focus on molecular identification of Xenopus Src and the signaling mechanism of the Src-dependent egg activation that has been established recently. We also summarize recent advances in understanding the role of the Src family kinases in egg fertilization of other model organisms, and discuss future directions of the field.     

Inhibition of joint inflammation and destruction induced by anti-type II collagen antibody/lipopolysaccharide (LPS)-induced arthritis in mice due to deletion of macrophage migration inhibitory factor (MIF)

OBJECTIVE: Previous studies have demonstrated that neutralization of macrophage migration inhibitory factor (MIF) by anti-MIF antibody decreases joint destruction in the collagen-induced arthritis model. The present study was undertaken to investigate whether selective deletion of MIF inhibits inflammation and joint destruction of the anti-type II collagen antibody (anti-CII Ab)/lipopolysaccharide (LPS)-induced arthritis in mice, in order to determine the role of this cytokine in inflammatory arthritis. DESIGN: Anti-CII Ab/LPS-induced arthritis was induced in MIF-deficient and wild-type mice. The effects of anti-MIF polyclonal antibody administration on anti-CII Ab-induced arthritis were also evaluated. RESULTS: The expression of MIF protein and mRNA was induced in anti-CII Ab/LPS-induced arthritis joint tissues. Histopathological arthritis scores for synovial inflammation induced by anti-CII Ab/LPS -induced arthritis were significantly decreased in anti-MIF Ab-treated mice and in MIF-deficient mice compared to wild-type mice. In addition, mRNA levels of MMP-13 and MIP-2 in anti-CII Ab/LPS-induced arthritis joint tissues were significantly reduced in MIF-deficient mice compared to wild-type control mice. CONCLUSIONS: These results indicate that MIF plays a critical role in inflammation and joint destruction in the anti-CII Ab/LPS-induced arthritis model in mice, in part via induction of MMP-13 and neutrophil infiltration through the induction of MIP-2.     

Homocysteine attenuates the expression of osteocalcin but enhances osteopontin in MC3T3-E1 preosteoblastic cells

It has been pointed out that very high plasma levels of homocysteine are characteristic of homocystinuria, a rare autosomal recessive disease accompanied by the early onset of generalized osteoporosis. However, it is unclear by which mechanism hyperhomocysteine induces osteoporosis, although it is known to interfere with the formation of cross-links in collagen, an essential process in bone formation. Therefore, we investigated the effect of homcysteine on expression of osteocalcin and osteopontin in MC3T3-E1 preosteoblastic cells. Confluent cells were grown in RPMI 1640 containing 10% fetal calf serum with or without homocysteine in an atmosphere of 95% humidified air, 5% CO2 at 37 degrees C. The secretion of osteocalcin from the cells increased time-dependently until the end of culture (day 34), but 500 microM homocysteine led to an approximately 61% decrease for osteocalcin after 19 days of culture as compared with the control. On the other hand, osteopontin was not inhibited by 500 microM homocysteine but rather activated, and ranged from 134%-209% of the control level in the period from 10 days until the end of culture. From analysis of RT-PCR for mRNA of osteocalcin and osteopontin at the end of the culture, homocysteine levels of 100 and 500 microM significantly increased the expression of osteopontin mRNA with the control (p < 0.05). In contrast, the expression of osteopontin mRNA was suppressed in a dose-dependent manner, showing a mirror image of the effect on osteopontin mRNA. These findings suggest that hyperhomocystenemia appears to be an independent risk factor for osteoporosis by disturbing osteoblast function.     

Contribution of macrophage migration inhibitory factor to extracellular signal-regulated kinase activation by oxidative stress in cardiomyocytes

In response to oxidative stress, the pathogenesis of a number of cardiovascular events and several genes are stimulated by extracellular signal-regulated kinases (ERK1/2). Biphasic (early, 10 min; and delayed, 120 min) ERK1/2 activation by H(2)O(2), a reactive oxygen species, was observed in cultured neonatal rat cardiomyocytes. We investigated the hypothesis that the delayed activation of ERK1/2 depends on a factor secreted by oxidative stress (FSO). The delayed activation was inhibited by calphostin C, a protein kinase C inhibitor. Conditioned medium (CM) obtained from cells stimulated with H(2)O(2) induced rapid and monophasic ERK1/2 activation, which was not inhibited by calphostin C. In contrast, calphostin C-pretreated CM did not activate ERK1/2. Macrophage migration inhibitory factor (MIF) was one of the candidate FSOs activating ERK1/2. The existence of MIF in CM, the recombinant MIF-stimulated ERK1/2 rapid activation, and anti-MIF neutralizing antibody-induced inhibition of the delayed activation implied that MIF could be the FSO. Pretreatment of cardiomyocytes with a mitogen-activated protein kinase/ERK kinase (MEK) inhibitor did not suppress the MIF secretion, although it prevented the ERK1/2 activation by H(2)O(2). These results indicate that MIF is secreted from cardiomyocytes as a result of oxidative stress and activates ERK1/2 through a MEK1/2-dependent mechanism, although the secretion is not regulated by ERK1/2 but by protein kinase C.     

Role of macrophage migration inhibitory factor in bleomycin-induced lung injury and fibrosis in mice

Macrophage migration inhibitory factor (MIF) is a unique cytokine that reportedly overrides the anti-inflammatory effect of endogenous glucocorticoids. MIF has been demonstrated to be involved in a variety of inflammatory diseases. In this study, we examined the role of MIF in bleomycin (BLM)-induced lung injury and fibrosis. The levels of MIF in lung tissues and bronchoalveolar lavage fluids were significantly increased in the period 5-10 days after intratracheal administration of BLM. Treatment with the anti-MIF antibody significantly reduced the mortality at 14 days and the histopathological lung injury score at 10 days. These effects were accompanied with significant suppression of the accumulation of inflammatory cells in the alveolar space and tumor necrosis factor-alpha in the lungs at 7 days. However, the anti-MIF antibody did not affect either the content of lung hydroxyproline or the histopathological lung fibrosis score at 21 days after BLM. These data provide further evidence for the crucial role of MIF in acute lung inflammation but do not support the involvement of MIF in lung fibrosis induced by BLM in mice.     

Menadione-linked α-glycerophosphate dehydrogenase activity of motoneurons in rat soleus and extensor digitorum longus neuron pools

After injection of horseradish peroxidase into the soleus (slow twitch) and extensor digitorum longus (fast twitch) muscles, glycolytic enzyme activity as reflected by -glycerophosphate dehydrogenase activity of labeled motoneurons in the neuron pool was examined. No differences were found in glycolytic enzyme activity of motoneurons between slow twitch and fast twitch neuron pools.     

Bradykinin Generation Triggered by Pseudomonas Proteases Facilitates Invasion of the Systemic Circulation by Pseudomonas aeruginosa

To elucidate the mechanism of bacterial exoprotease in promotion of the intravascular dissemination of Pseudomonas aeruginosa, we examined the possible involvement of bradykinin (whose generation is induced by pseudomonal proteases in septic foci) in the invasion by bacteria, and in access of bacterial toxins to systemic blood circulation. P. aeruginosa 621 (PA 621), which produces very little protease, was injected intraperitoneally into mice together with pseudomonal exoproteases (elastase/alkaline protease). Dissemination of bacteria from the peritoneal septic foci to the blood was assessed by counting viable bacteria in the blood and spleen by use of the colony-forming assay. The results showed that pseudomonal proteases markedly enhanced (10- to 100-fold) intravascular dissemination of bacteria in mice. This enhancement was induced not only by pseudomonal proteases but also by bradykinin. More importantly, the increased spread of PA 621 induced by pseudomonal protease and bradykinin was significantly augmented by the addition of kininase inhibitors, indicating the direct involvement of bradykinin in bacterial dissemination. Similarly, bradykinin caused effective dissemination of pseudomonal toxins such as endotoxin (lipopolysaccharide) and exotoxin A when the toxins were injected into the peritoneal cavity with bradykinin. Furthermore, the lethality of the infection with PA 621 was strongly enhanced by pseudomonal proteases given i.p. simultaneously with PA 621. On the basis of these results, it is strongly suggested that pseudomonal proteases as well as bradykinin generated in infectious foci are involved in facilitation of bacterial dissemination in vivo.     

Crystal structure of human D-dopachrome tautomerase, a homologue of macrophage migration inhibitory factor, at 1.54 A resolution

D-Dopachrome tautomerase shares a low homologous amino acid sequence (33% homology) with the macrophage migration inhibitory factor (MIF) and possesses similar tautomerase activity as well. MIF is a cytokine involved in inflammatory reactions and immune responses. Whereas recent studies have identified MIF as a pituitary hormone and immunoregulator, much less is known about the structural basis of these physiological functions and the real significance of tautomerase activity. Therefore, interest in the structure-function relationship between D-dopachrome tautomerase and MIF has increased, especially with regard to inflammation and immune responses. We have determined the X-ray crystal structure of human D-dopachrome tautomerase at 1.54 A resolution. D-Dopachrome tautomerase folds to form a homotrimer that has extensive contact between subunits by intersubunit beta-sheets. Its overall topology and trimeric formations are similar to those of human MIF. The N-terminal proline is located at the bottom of a positively charged pocket in which the conformations of Lys32 and Ser63 are highly conserved. These positively charged properties are also seen in the active site pocket of human MIF, bacterial 5-(carboxymethyl)-2-hydroxymuconate isomerase (CHMI), and 4-oxalocrotonate tautomerase (4-OT). A detailed comparison of these structures revealed significant differences in the environment around the potential active site, the intersubunit contacts, and charge distribution on the molecular surface. It can be concluded that these features are related to the physiological role and tautomerase activity of MIF and D-dopachrome tautomerase. The present structural study could be helpful for designing effective inhibitors that modulate immunoregulatory and hormone-like effects.