Complete mitochondrial genomes of prasinophyte algae Pyramimonas parkeae and Cymbomonas tetramitiformis

Mitochondria are archetypal eukaryotic organelles that were acquired by endosymbiosis of an ancient species of alpha‐proteobacteria by the last eukaryotic common ancestor. The genetic information contained within the mitochondrial genome has been an important source of information for resolving relationships among eukaryotic taxa. In this study, we utilized mitochondrial and chloroplast genomes to explore relationships among prasinophytes. Prasinophytes are represented by diverse early‐diverging green algae whose physical structures and genomes have the potential to elucidate the traits of the last common ancestor of the Viridiplantae (or Chloroplastida). We constructed de novo mitochondrial genomes for two prasinophyte algal species, Pyramimonas parkeae and Cymbomonas tetramitiformis, representing the prasinophyte clade. Comparisons of genome structure and gene order between these species and to those of other prasinophytes revealed that the mitochondrial genomes of P. parkeae and C. tetramitiformis are more similar to each other than to other prasinophytes, consistent with other molecular inferences of the close relationship between these two species. Phylogenetic analyses using the inferred amino acid sequences of mitochondrial and chloroplast protein‐coding genes resolved a clade consisting of P. parkeae and C. tetramitiformis; and this group (representing the prasinophyte clade I) branched with the clade II, consistent with previous studies based on the use of nuclear gene markers.     

Fatty acid synthesis is critical for stem cell pluripotency via promoting mitochondrial fission

Pluripotent stem cells are known to display distinct metabolic phenotypes than their somatic counterparts. While accumulating studies are focused on the roles of glucose and amino acid metabolism in facilitating pluripotency, little is known regarding the role of lipid metabolism in regulation of stem cell activities. Here, we show that fatty acid (FA) synthesis activation is critical for stem cell pluripotency. Our initial observations demonstrated enhanced lipogenesis in pluripotent cells and during cellular reprogramming. Further analysis indicated that de novo FA synthesis controls cellular reprogramming and embryonic stem cell pluripotency through mitochondrial fission. Mechanistically, we found that de novo FA synthesis regulated by the lipogenic enzyme ACC1 leads to the enhanced mitochondrial fission via (i) consumption of AcCoA which affects acetylation‐mediated FIS1 ubiquitin–proteasome degradation and (ii) generation of lipid products that drive the mitochondrial dynamic equilibrium toward fission. Moreover, we demonstrated that the effect of Acc1 on cellular reprogramming via mitochondrial fission also exists in human iPSC induction. In summary, our study reveals a critical involvement of the FA synthesis pathway in promoting ESC pluripotency and iPSC formation via regulating mitochondrial fission.     

Prohibitin involvement in the generation of mitochondrial superoxide at complex I in human sperm

Prohibitin (PHB), a major mitochondrial membrane protein, has been shown earlier in our laboratoryto regulate sperm motility via an alteration in mitochondrial membrane potential (MMP) in infertile men with poor sperm quality. To test if PHB expression is associated with sperm mitochondrial superoxide (mROS) levels, here we examined sperm mROS levels, high MMP and lipid peroxidation in infertile men with poor sperm motility (asthenospermia, A) and/or low sperm concentrations (oligoasthenospermia, OA). The diaphorase‐type activity of sperm mitochondrial complex I (MCI) and PHB expression were also determined. We demonstrate that mROS and lipid peroxidation levels are significantly higher in sperm from A and OA subjects than in normospermic subjects, whereas high MMP and PHB expression are significantly lower. A positive correlation between mROS and lipid peroxidation and a negative correlation of mROS with PHB expression, high MMP, and sperm motility were found in these subjects. The finding of similar diaphorase‐type activity levels of sperm MCI in the three groups studied suggests that the catalytic subunits of MCI in the matrix arm may produce mROS on its own. There may be a dysfunction of electron transport at MCI associated with decreased expression of PHB in sperm with poor quality. We conclude that mROS level is increased and associated with decreased PHB expression, and it may regulate sperm motility via increases in low MMP and lipid peroxidation. This is the first report on the involvement of PHB in human sperm motility loss associated with increased generation of mROS at MCI.     

Hierarchically Structured 3D Integrated Electrodes by Galvanic Replacement Reaction for Highly Efficient Water Splitting

A NiFe‐based integrated electrode is fabricated by the spontaneous galvanic replacement reaction on an iron foam. Driven by the different electrochemical potentials between Ni and Fe, the dissolution of surface Fe occurs with electroless plating of Ni on iron foam with no need to access instrumentation and input energy. A facile cyclic voltammetry treatment is subsequently applied to convert the metallic NiFe to NiFeO_x . A series of analytical methods indicates formation of a NiFeO_x film of nanosheets on the iron foam surface. This hierarchically structured three dimensional electrode displays high activity and durability against water oxidation. In 1 m KOH, a current density of 1000 mA cm^?2 is achieved at an overpotential of only 300 mV. This method is readily extended to fabricate CoFe or NiCoFe‐based integrated electrodes for water oxidation. Phosphorization of the bimetallic oxide (NiFeO_x ) generates the bimetallic phosphide (NiFe‐P), which can act as an excellent electrocatalyst for hydrogen production in 1 m KOH. An alkaline electrolyzer is constructed using NiFeO_x and NiFe‐P coated iron foams as anode and cathode, which can realize overall water splitting with a current density of 100 mA cm^?2 at an overpotential of 630 mV.     

The first complete mitogenome of the South China deep‐sea giant isopod Bathynomus sp. (Crustacea: Isopoda: Cirolanidae) allows insights into the early mitogenomic evolution of isopods

In this study, the complete mitochondrial (mt) genome sequence of the South China deep‐sea giant isopod Bathynomus sp. was determined, and this study is the first to explore in detail the mt genome of a deep‐sea member of the order Isopoda. This species belongs to the genus Bathynomus, the members of which are saprophagous residents of the deep‐sea benthic environment; based on their large size, Bathynomus is included in the “supergiant group” of isopods. The mt genome of Bathynomus sp. is 14,965 bp in length and consists of 13 protein‐coding genes, two ribosomal RNA genes, only 18 transfer RNA genes, and a noncoding control region 362 bp in length, which is the smallest control region discovered in Isopoda to date. Although the overall genome organization is typical for metazoans, the mt genome of Bathynomus sp. shows a number of derived characters, such as an inversion of 10 genes when compared to the pancrustacean ground pattern. Rearrangements in some genes (e.g., cob, trnT, nad5, and trnF) are shared by nearly all isopod mt genomes analyzed thus far, and when compared to the putative isopod ground pattern, five rearrangements were found in Bathynomus sp. Two tRNAs exhibit modified secondary structures: The TΨC arm is absent from trnQ, and trnC lacks the DHU. Within the class Malacostraca, trnC arm loss is only found in other isopods. Phylogenetic analysis revealed that Bathynomus sp. (Cymothoida) and Sphaeroma serratum (Sphaeromatidea) form a single clade, although it is unclear whether Cymothoida is monophyletic or paraphyletic. Moreover, the evolutionary rate of Bathynomus sp. (dN/dS [nonsynonymous mutational rate/synonymous mutational rate] = 0.0705) is the slowest measured to date among Cymothoida, which may be associated with its relatively constant deep‐sea environment. Overall, our results may provide useful information for understanding the evolution of deep‐sea Isopoda species.     

Rates and relations of mitochondrial genome evolution across the Echinoidea,with special focus on the superfamily Odontophora

In order to better characterize the placement of genus Tripneustes, as a representative of the Toxopneustidae family within the broader sea urchin mitochondrial (MT) phylogeny, the complete MT genome of Tripneustes gratilla was generated and compared with all published echinoid MT genomes currently available on NCBI GenBank. The MT genome phylogeny supports the existence of the superfamily Odontophora (consisting of the families Strongylocentrotidae, Echinometridae, and Toxopneustidae). A relaxed molecular‐clock time calibration suggests a split between the three key Odontophore MT lineages occurred during the late Eocene/Oligocene. Major global oceanographic changes have been inferred during this time frame, potentially driving species diversification through environmental selection pressures. To test for signatures of selection acting on the mitochondria, the historical rate of gene evolution of individual MT genes was assessed through a branch‐site comparison of nonsynonymous to synonymous substitution ratios (ω). Models of positive selection and neutral evolution, as compared via a likelihood ratio test, show no evidence of strong historical positive selection on mitochondrial genes at the genesis of the Odontophora. However, while pairwise ω comparison revealed signatures of strong negative selection, relatively elevated ω values were observed within the Strongylocentrotus genus.     

植物光合CO2响应模型对光下(暗)呼吸速率拟合的探讨

运用LI-6400便携式光合作用系统测定了不同光强(2000、1500、1000和500 μmol·m^-2·s^-1)和两种O₂浓度(21%和2%的O₂)下冬小麦(Triticum aestivum)灌浆期旗叶的CO₂响应曲线, 比较了现有CO₂响应模型(生化模型、直角双曲线模型和直角双曲线修正模型)拟合给出光下(暗)呼吸与测量值之间的差异。结果显示, 直角双曲线修正模型所给出的光下呼吸速率拟合值与测量值最为接近。植物光合作用对大气CO₂响应(A/C_a)的拟合结果优于光合作用对胞间CO₂浓度(A/C_i)的拟合。然而, 所有模型基于A/C_a拟合的光下(暗)呼吸在整体上与测量值存在显著差异(p < 0.05), 推测与现有模型没有考虑CO₂浓度对光呼吸和光下暗呼吸速率的影响有关。对小麦的试验结果表明, CO₂浓度对光呼吸和光下暗呼吸均有显著影响: 随着CO₂浓度的增加(0-1400 μmol·mol^-1), 不同光强下的表观光呼吸变化范围分别为5.035-11.670、4.222-11.650、4.330-10.999和3.263-9.094 μmol CO_2·m^-2·s^-1; 光下暗呼吸的变化范围分别为0.491-2.987、0.457-2.955、0.545-3.139和0.448-3.139 μmol CO₂·m^-2·s^-1。回归分析发现, 表观光呼吸和光下暗呼吸与CO₂浓度之间均存在较好的相关性。然而, 将该回归关系整合到现有模型中, 是否会优化模型, 从而提高模型对相关光合参数估算的准确性尚有待于进一步研究。     

Conservation and versatility of a new set of primers for long‐PCR amplification of complete insect mitochondrial genomes based on Haematobia irritans mtDNA sequences

The amplification of complete mitochondrial genomes by long PCR (polymerase chain reaction) has been a major contribution to the large‐scale sequencing of arthropodan mitochondrial genomes. In this work, we designed six conserved long‐PCR primers to successfully recover the entire mitochondrial genome of the horn fly Haematobia irritans (Diptera: Muscidae) in two overlapping fragments. The conservation and versatility of these primers were tested for 17 other species from four major insect orders: Diptera (14), Coleoptera (1), Lepidoptera (1) and Hymenoptera (1). The amplification of complete mitochondrial genomes in orders other than Diptera suggested an even broader application of these primers, especially within the Hexapoda.     

Tyroserleutide tripeptide affects calcium homeostasis of human hepatocarcinoma BEL-7402 cells

Copyright by Science in China Press 2005 Primary hepatocarcinoma is one of the most fre-quent digestive-tract cancers, particularly in China. The incidence and death rate of primary hepatocarci-noma in China is the highest in the world, with about 1100 thousands people dying from primary hepatocar-cinoma per year[1]. Although the chemotherapeutic agents are the main therapeutic approach for hepato- carcinoma, they are relatively ineffective and result in many toxic and side effects. Accordin…