Different Predation Impacts of Two Cyclopoid Species on a Small-sized Zooplankton Community: An Experimental Analysis with Mesocosms

We used mesocosms to analyze predation impacts on the prey populations and prey community structures by two cyclopoid copepod species, the larger Mesocyclops pehpeiensis and the smaller Thermocyclops taihokuensis, who coexist with small-sized herbivorous zooplankton species in a fish-abundant lake. The overall predation impact on the prey populations was stronger for Mesocyclops than for Thermocyclops. Mesocyclops had a strong and less selective impact on the rotifer community but a selective impact on the crustaceans. In contrast, Thermocyclops had a selective predation impact on rotifers but a weak and less selective impact on the crustacean community. As a result, the former predator reduced the diversity of the crustacean community but not the rotifer community, while the latter had an opposite impact on the diversities of the two communities. It has been suggested that fish induce development of a zooplankton community dominated by the small-sized zooplankton species in fish-abundant lakes. Our results demonstrated that cyclopoid copepods altered species composition and diversity of the small-sized zooplankton community in such lakes. Thus, the results have given an important suggestion on the role of the invertebrate predator cyclopoid copepods, which often coexist with fish, that they determine population dynamics and community structures of small-sized zooplankton in fish-abundant lakes.     

Derlin-2 and Derlin-3 are regulated by the mammalian unfolded protein response and are required for ER-associated degradation

Proteins that are unfolded or misfolded in the endoplasmic reticulum (ER) must be refolded or degraded to maintain the homeostasis of the ER. Components of both productive folding and ER-associated degradation (ERAD) mechanisms are known to be up-regulated by the unfolded protein response (UPR). We describe two novel components of mammalian ERAD, Derlin-2 and -3, which show weak homology to Der1p, a transmembrane protein involved in yeast ERAD. Both Derlin-2 and -3 are up-regulated by the UPR, and at least Derlin-2 is a target of the IRE1 branch of the response, which is known to up-regulate ER degradation enhancing alpha-mannosidase-like protein (EDEM) and EDEM2, receptor-like molecules for misfolded glycoprotein. Overexpression of Derlin-2 or -3 accelerated degradation of misfolded glycoprotein, whereas their knockdown blocked degradation. Derlin-2 and -3 are associated with EDEM and p97, a cytosolic ATPase responsible for extraction of ERAD substrates. These findings indicate that Derlin-2 and -3 provide the missing link between EDEM and p97 in the process of degrading misfolded glycoproteins.     

Exploration of genes showing intramuscular fat deposition-associated expression changes in musculus longissimus muscle

Marbling, as defined by the amount of intramuscular fat, is an economically important trait in beef cattle. Intramuscular fat deposition is postulated to arise mainly from a series of adipogenic events in intramuscular adipocyte-lineage cells and in the physiological or anatomical milieux surrounding them. This study was designed to investigate gene-expression patterns associated with fat deposition in musculus longissimus muscle, including adipocyte-lineage cells and part of the milieux. Differential-display PCR (ddPCR) was used to examine expression differences between low-marbled and high-marbled steer groups at 8, 10, 12 and 14 months of age, encompassing the time that marbling starts to appear. Seventy-four of 2114 total bands on ddPCR gel-bands were significant (P < 0.05) for the group effect, the interaction effect between group and age, or both the group and the interaction effects. Sequence analysis of 72 of these bands revealed 77 genes, including 35 annotated genes and 42 novel sequences. Among the 35 annotated genes, 6 (BTG2, PDHB, SORBS1, TRDN, TTN and MGP) have been related to changes in intramuscular fat deposition, possibly by exerting effects on adipocyte-lineage cells or on the milieux surrounding them.     

Cytosolic chaperonin prevents polyglutamine toxicity with altering the aggregation state

Polyglutamine (polyQ)-expansion proteins cause neurodegenerative disorders including Huntington's disease, Kennedy's disease and various ataxias. The cytotoxicity of these proteins is associated with the formation of aggregates or other conformationally toxic species. Here, we show that the cytosolic chaperonin CCT (also known as TRiC) can alter the course of aggregation and cytotoxicity of huntingtin (Htt)-polyQ proteins in mammalian cells. Disruption of the CCT complex by RNAi-mediated knockdown enhanced Htt-polyQ aggregate formation and cellular toxicity. Analysis of the aggregation states of the Htt-polyQ proteins by fluorescence correlation spectroscopy revealed that CCT depletion results in the appearance of soluble Htt-polyQ aggregates. Similarly, overexpression of all eight subunits of CCT suppressed Htt aggregation and neuronal cell death. These results indicate that CCT has an essential role in protecting against the cytotoxicity of polyQ proteins by affecting the course of aggregation.     

VDAC1, having a shorter N-terminus than VDAC2 but showing the same migration in an SDS-polyacrylamide gel, is the predominant form expressed in mitochondria of various tissues

The voltage-dependent anion channel (VDAC) is a pore-forming protein expressed in the outer membrane of eukaryotic mitochondria. Three isoforms of it, i.e., VDAC1, VDAC2, and VDAC3, are known to be expressed in mammals; however, the question as to which is the main isoform in mitochondria is still unanswered. To address this question, we first prepared standard VDACs by using a bacterial expression system and raised various antibodies against them by using synthetic peptides as immunogens. Of the three bacterially expressed VDAC isoforms, VDAC3 showed faster migration in SDS-polyacrylamide gels than VDAC1 and VDAC2, although VDAC2 is longer than VDAC1 and VDAC3, due to a 12-amino acid extension of its N-terminal region. Even with careful structural characterization of the expressed VDACs by LC-MS/MS analysis, serious structural modifications of VDACs causing changes in their migration in SDS-polyacrylamide gels were not detected. Next, immunoreactivities of the raised antibodies toward these bacterially expressed VDAC isoforms were evaluated. Trials to prepare specific antibodies against the three individual VDAC isoforms were not successful except in the case of VDAC1. However, using a synthetic peptide corresponding to the highly conserved region among the three VDACs, we were successful in preparing an antibody showing essentially equal immunoreactivities toward all three VDACs. When mitochondrial outer membrane proteins of various rat tissues were subjected to 2-dimensional electrophoresis followed by immunoblotting with this antibody, six immunoreactive protein spots were detected. These spots were characterized by LC-MS/MS analysis, and the signal intensities among the spots were compared. As a result, the signal intensity of the spot representing VDAC1 was the highest, and thus, VDAC1 was concluded to be the most abundantly expressed of the three VDAC isoforms in mammalian mitochondria.     

Growth inhibition by metabolites of gamma-hexachlorocyclohexane in Sphingobium japonicum UT26

The growth of a gamma-hexachlorocyclohexane (gamma-HCH)-degrading bacterium Sphingobium japonicum (formerly Sphingomonas paucimobilis) UT26 in rich medium was inhibited by gamma-HCH. This growth inhibition was not observed in a mutant that lacked the initial or second step enzymatic activity for gamma-HCH degradation, suggesting that metabolites of gamma-HCH are toxic to UT26. Two metabolites of gamma-HCH, 2,5-dichlorophenol (2,5-DCP) and 2,5-dichlorohydroquinone (2,5-DCHQ), showed a direct toxic effect on UT26 and other sphingomonad strains. Because only 2,5-DCP accumulated during gamma-HCH degradation, 2,5-DCP is thought to be a main compound for growth inhibition.     

Dietary sterol preference in the silkworm, Bombyx mori

Since insects are unable to biosynthesize sterols de novo, sterols must be obtained from dietary sources. Although it has been reported that beta-sitosterol is crucial for larval growth in the silkworm, Bombyx mori, little has been investigated concerning the dietary selection of sterols by Bombyx larvae. Here, we demonstrate that Bombyx larvae have the following sterol preference: beta-sitosterol > ergosterol > cholesterol = stigmasterol. Interestingly, Bombyx larvae preferred ergosterol, an inhibitory sterol on larval growth, indicating that sterol selection following first contact of the diet with the mouth part might be different from the sterol recognition mechanism present in sterol metabolism.     

Degradation of human hemoglobin by Prevotella intermedia

In this study, the ability of Prevotella intermedia, an obligate anaerobic rod, to degrade human hemoglobin was determined by SDS-PAGE and the degradation was quantified by scanning densitometry. Both bacterial cells and culture supernatants degraded hemoglobin. The hemoglobin degradation by P. intermedia was time-dependent, heat sensitive, pH related and was not influenced by iron restriction. Inhibition studies demonstrated that a cysteine protease might be involved in hemoglobin degradation and this protease might require metal ions for its activity and it might be thiol-requiring and trypsin-inducible. The results indicate that P. intermedia is capable to release heme from hemoglobin, hence provide a source of iron for its proliferation.