A novel RNA-recognition-motif protein is required for premeiotic G1/S-phase transition in rice (Oryza sativa L.)

The molecular mechanism for meiotic entry remains largely elusive in flowering plants. Only Arabidopsis SWI1/DYAD and maize AM1, both of which are the coiled-coil protein, are known to be required for the initiation of plant meiosis. The mechanism underlying the synchrony of male meiosis, characteristic to flowering plants, has also been unclear in the plant kingdom. In other eukaryotes, RNA-recognition-motif (RRM) proteins are known to play essential roles in germ-cell development and meiosis progression. Rice MEL2 protein discovered in this study shows partial similarity with human proline-rich RRM protein, deleted in Azoospermia-Associated Protein1 (DAZAP1), though MEL2 also possesses ankyrin repeats and a RING finger motif. Expression analyses of several cell-cycle markers revealed that, in mel2 mutant anthers, most germ cells failed to enter premeiotic S-phase and meiosis, and a part escaped from the defect and underwent meiosis with a significant delay or continued mitotic cycles. Immunofluorescent detection revealed that T7 peptide-tagged MEL2 localized at cytoplasmic perinuclear region of germ cells during premeiotic interphase in transgenic rice plants. This study is the first report of the plant RRM protein, which is required for regulating the premeiotic G1/S-phase transition of male and female germ cells and also establishing synchrony of male meiosis. This study will contribute to elucidation of similarities and diversities in reproduction system between plants and other species.     

The novel gene HOMOLOGOUS PAIRING ABERRATION IN RICE MEIOSIS1 of rice encodes a putative coiled-coil protein required for homologous chromosome pairing in meiosis

We have identified and characterized a novel gene, PAIR1 (HOMOLOGOUS PAIRING ABERRATION IN RICE MEIOSIS1), required for homologous chromosome pairing and cytokinesis in male and female meiocytes of rice (Oryza sativa). The pair1 mutation, tagged by the endogenous retrotransposon Tos17, exhibited meiosis-specific defects and resulted in complete sterility in male and female gametes. The PAIR1 gene encodes a 492-amino acid protein, which contains putative coiled-coil motifs in the middle, two basic regions at both termini, and a potential nuclear localization signal at the C terminus. Expression of the PAIR1 gene was detected in the early stages of flower development, in which the majority of the sporocytes had not entered meiosis. During prophase I of the pair1 meiocyte, all the chromosomes became entangled to form a compact sphere adhered to a nucleolus, and homologous pairing failed. At anaphase I and telophase I, chromosome nondisjunction and degenerated spindle formation resulted in multiple uneven spore production. However, chromosomal fragmentation frequent in plant meiotic mutants was never observed in all of the pair1 meiocytes. These observations clarify that the PAIR1 protein plays an essential role in establishment of homologous chromosome pairing in rice meiosis.     

Further discussion about the features of Lake Puma Yum Co, South Tibet, China

Further discussion about the limnological features of Lake Puma Yum Co, South Tibet, China, is provided based on the results of several investigations. By using depth data from all over the lake, the whole submarine topography has been compiled. Horizontal analysis of the water's physicochemical features indicates that compared with the relatively uniform water features at other lake areas, apparent spatial heterogeneity exists in the water of the subaquatic alluvial fan induced by the Jiaqu River, the biggest inflow. Vertical analysis of water characteristics using two-factor analysis of variance with no re-experiment indicates that temperature, dissolved oxygen, and pH of the water vary with water depth rhythmically, whereas other parameters demonstrate no evident vertical variation, which shows that chemical stratification is not obvious. But this does not exclude slightly higher concentrations of Ca²⁺ induced by lower pH at the bottom of deep lake water. The hydrochemistry difference between inflow water and lake water reveals the loss of Ca²⁺ in lake water, which indicates calcite deposition may be an important characteristic of lake sediment.     

Free Radicals and Sod Activity of Jaw Cyst. Direct Measurement and Spin Trapping Studies by Esr

Free radicals produced in the fluid of jaw cysts were directly measured at room temperature using ESR. With these samples, SOD activity of the cyst fluid was measured by the ESR spin trapping method with DMPO as a trapping agent. Freeze-dried samples of cyst fluid showed a broad ESR signal at g = 2.005. Relative signal intensity of samples from jaw cysts with inflammation was higher than jaw cysts without inflammation. SOD activity of cyst fluid with high viscosity showed higher values than that of cyst fluid with low viscosity. We suggest that free radicals produced in jaw cyst damage tissues while higher SOD activity of cyst fluid play a role in a self-defense mechanism against free radicals.     

Elucidations of the Catalytic Cycle of NADH-Cytochrome b5 Reductase by X-ray Crystallography: New Insights into Regulation of Efficient Electron Transfer

NADH-Cytochrome b₅ reductase (b5R), a flavoprotein consisting of NADH and flavin adenine dinucleotide (FAD) binding domains, catalyzes electron transfer from the two-electron carrier NADH to the one-electron carrier cytochrome b₅ (Cb5). The crystal structures of both the fully reduced form and the oxidized form of porcine liver b5R were determined. In the reduced b5R structure determined at 1.68 Å resolution, the relative configuration of the two domains was slightly shifted in comparison with that of the oxidized form. This shift resulted in an increase in the solvent-accessible surface area of FAD and created a new hydrogen-bonding interaction between the N5 atom of the isoalloxazine ring of FAD and the hydroxyl oxygen atom of Thr66, which is considered to be a key residue in the release of a proton from the N5 atom. The isoalloxazine ring of FAD in the reduced form is flat as in the oxidized form and stacked together with the nicotinamide ring of NAD⁺. Determination of the oxidized b5R structure, including the hydrogen atoms, determined at 0.78 Å resolution revealed the details of a hydrogen-bonding network from the N5 atom of FAD to His49 via Thr66. Both of the reduced and oxidized b5R structures explain how backflow in this catalytic cycle is prevented and the transfer of electrons to one-electron acceptors such as Cb5 is accelerated. Furthermore, crystallographic analysis by the cryo-trapping method suggests that re-oxidation follows a two-step mechanism. These results provide structural insights into the catalytic cycle of b5R.     

Modulation of extracellular conditions prevents the multilayering of the simple epithelium

Simple epitheliums in normal glandular systems are regulated not to stratify even though the constituent cells proliferate and will rise from the epithelium. Since epithelial cells have the potential to establish cell–cell adhesions, the avoidance of stratification must be related to the intracellular signal cascades and the extracellular conditions. The contributions of the former are becoming clarified, but the influence of the latter is poorly understood. In the present study, we examined whether the frequency of cell-on-cell adhesion, which mimics the early stage of multilayering, is dependent on the type of the extracellular scaffold protein. Wild-type epithelial cells were cultured on E-cadherin-Fc (a cell–cell adhesion protein) or collagen (an extracellular matrix protein), and then, green fluorescent protein (GFP)-positive cells were seeded onto these wild-type cells. We observed that the cell-on-cell adhesion (adhesion of the GFP-positive cell to the wild-type cells) was more frequent in the E-cadherin-Fc treatment than the collagen treatment. The cell-on-cell adhesions that were observed in the E-cadherin treatment were transient and decreased in frequency to that of the collagen treatment after the 12 h of cell culture. We observed the disappearance of E-cadherin-Fc but not collagen during cell culture. These results suggest that transient multilayering in simple epithelium is possible, depending on the types of extracellular scaffold protein, and they imply that cells can modify the extracellular conditions to meet normal cellular conditions.     

Characterization of myeloid cells derived from the anterior ventral mesoderm in the Xenopus laevis embryo

A recent study revealed the presence of a unique population of myeloid cells in the anterior ventral (AV) mesoderm of Xenopus laevis embryo, as characterized by the expression of peroxidase 2 (POX2), which encodes for a leukocyte-specific enzyme. The current report further characterized the POX2-positive cells in terms of their contribution to hematopoiesis in tadpole and regulatory mechanism in differentiation. Grafting experiments with cytogenetically labeled tissues revealed that AV-derived mesoderm supplies a transient population of migrating leukocytes in the mesenchyme of early tadpole. These cells were rarely found in blood vessels at any stages. Using a ventral marginal zone explant system, we demonstrated that dkk1, shown as a heart inducer in this system, has a strong ability to induce the expression of POX2. Injection of a high dose dkk1 RNA induced a heart marker while a low dose of dkk1 preferentially induced the expression of POX2, suggesting that dkk1 works as a morphogen to determine the different lineages. Overall results indicate that wnt signal inhibitors induce leukocytes at the early neurula stage and that these cells spread to the entire body and exist until the ventral blood island-derived leukocytes appear in the body.