The plant-like C2 glycolate cycle and the bacterial-like glycerate pathway cooperate in phosphoglycolate metabolism in cyanobacteria

The occurrence of a photorespiratory 2-phosphoglycolate metabolism in cyanobacteria is not clear. In the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we have identified open reading frames encoding enzymes homologous to those forming the plant-like C2 cycle and the bacterial-type glycerate pathway. To study the route and importance of 2-phosphoglycolate metabolism, the identified genes were systematically inactivated by mutagenesis. With a few exceptions, most of these genes could be inactivated without leading to a high-CO(2)-requiring phenotype. Biochemical characterization of recombinant proteins verified that Synechocystis harbors an active serine hydroxymethyltransferase, and, contrary to higher plants, expresses a glycolate dehydrogenase instead of an oxidase to convert glycolate to glyoxylate. The mutation of this enzymatic step, located prior to the branching of phosphoglycolate metabolism into the plant-like C2 cycle and the bacterial-like glycerate pathway, resulted in glycolate accumulation and a growth depression already at high CO(2). Similar growth inhibitions were found for a single mutant in the plant-type C2 cycle and more pronounced for a double mutant affected in both the C2 cycle and the glycerate pathway after cultivation at low CO(2). These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO(2), glycine decarboxylase knockout mutants accumulated far more glycine and lysine than wild-type cells or mutants with inactivated glycerate pathway. This finding and the growth data imply a dominant, although not exclusive, role of the C2 route in cyanobacterial phosphoglycolate metabolism.     

Origin of the prechordal plate and patterning of the anteroposterior regional specificity of the involuting and extending archenteron roof of a urodele, Cynops pyrrhogaster

We analyzed the notochord formation, formation of the prechordal plate, and patterning of anteroposterior regional specificity of the involuting and extending archenteron roof of a urodele, Cynops pyrrhogaster. The lower (LDMZ) and upper (UDMZ) domains of the dorsal marginal zone (DMZ) of the early gastrula involuted and formed two distinct domains: the anterior fore-notochordal endodermal roof and the posterior domain containing the prospective notochord. Cygsc is expressed in the LDMZ from the onset of gastrulation, and the Cygsc-expressing LDMZ planarly induces the notochord in the UDMZ at the early to mid gastrula stages. At the mid to late gastrula stages, part of the Cygsc-expressing LDMZ is confined to the prechordal plate. On the other hand, Cybra expression only begins at mid gastrula stage, coincident with notochord induction at this stage. Anteroposterior regional specificity of the neural plate was patterned by the posterior domain of the involuting archenteron roof containing the prospective notochord at the mid to late gastrula stages. Cynops gastrulation thus differs significantly from Xenopus gastrulation in that the regions of the DMZ are specified from the onset of gastrulation, while the equivalent state of specification does not occur in Cynops until the middle of gastrulation. Thus we propose that Cynops gastrulation is divided into two phases: a notochord induction phase in the early to mid gastrula, and a neural induction phase in the mid to late gastrula.     

Chromosomal features of nucleolar dominance in hybrids between the Neotropical fish <Emphasis Type="Italic">Leporinus macrocephalus</Emphasis> and <Emphasis Type="Italic">Leporinus elongatus</Emphasis> (Characiformes,Anostomidae)

In the present study, the chromosomal mechanisms of nucleolar dominance were analyzed in the hybrid lineage “Piaupara,” which resulted from crossing the Leporinus macrocephalus female (Piauçu) and L. elongatus male (Piapara) fish. The analyses demonstrated that, in the hybrid, the nucleolar region inherited from L. elongatus presented higher activity, with expression in 100% of the cells, whereas the nucleolar region from L. macrocephalus appeared active at a frequency of 11.6%. The FISH technique with an 18S probe showed that the ribosomal DNA of the nucleolar region was not lost in the hybrid, and the results therefore demonstrated invariable marks in two chromosomes, each originating from one parent. An interesting difference between the nucleolar regions of the parental species was the association of the NOR with heterochromatic blocks (repetitive DNA) in L. elongatus, which could act as a determinative element in the establishment of this process.     

Mechanism of the Chaperone-like and Antichaperone Activities of Amyloid Fibrils of Peptides from αA-Crystallin

The amyloid fibril of a fragment of the substrate binding site of αA-crystallin (αAC(71-88)) exhibited chaperone-like activity by suppressing the aggregation of alcohol dehydrogenase (ADH) and luciferase. By contrast, the amyloid fibril of the cytotoxic fragment of amyloid β protein (Aβ(25-35)) facilitated the aggregation of the same proteins. We have determined the zeta potential of the amyloid fibril by measuring their electrophoretic mobility to study the effects of the surface charge on the modulation of protein aggregation. The αAC(71-88) amyloid possesses a large negative zeta potential value which is unaffected by the binding of the negatively charged ADH, indicating that the αAC(71-88) amyloid is stable as a colloidal dispersion. By contrast, the Aβ(25-35) amyloid possesses a low zeta potential value, which was significantly reduced with the binding of the negatively charged ADH. The canceling of the surface charge of the amyloid fibril upon substrate binding reduces colloidal stability and thereby facilitates protein aggregation. These results indicate that one of the key factors determining whether amyloid fibrils display chaperone-like or antichaperone activity is their electrostatic interaction with the substrate. The surface of the αAC(71-88) amyloid comprises a hydrophobic environment, and the chaperone-like activity of the αAC(71-88) amyloid is best explained by the reversible substrate binding driven by hydrophobic interactions. On the basis of these findings, we designed variants of amyloid fibrils of αAC(71-88) that prevent protein aggregation associated with neurodegenerative disorders.     

Induction of metallothionein in mouse cerebellum and cerebrum with low-dose thimerosal injection

Thimerosal, an ethyl mercury compound, is used worldwide as a vaccine preservative. We previously observed that the mercury concentration in mouse brains did not increase with the clinical dose of thimerosal injection, but the concentration increased in the brain after the injection of thimerosal with lipopolysaccharide, even if a low dose of thimerosal was administered. Thimerosal may penetrate the brain, but is undetectable when a clinical dose of thimerosal is injected; therefore, the induction of metallothionein (MT) messenger RNA (mRNA) and protein was observed in the cerebellum and cerebrum of mice after thimerosal injection, as MT is an inducible protein. MT-1 mRNA was expressed at 6 and 9 h in both the cerebrum and cerebellum, but MT-1 mRNA expression in the cerebellum was three times higher than that in the cerebrum after the injection of 12 μg/kg thimerosal. MT-2 mRNA was not expressed until 24 h in both organs. MT-3 mRNA was expressed in the cerebellum from 6 to 15 h after the injection, but not in the cerebrum until 24 h. MT-1 and MT-3 mRNAs were expressed in the cerebellum in a dose-dependent manner. Furthermore, MT-1 protein was detected from 6 to 72 h in the cerebellum after 12 μg/kg of thimerosal was injected and peaked at 10 h. MT-2 was detected in the cerebellum only at 10 h. In the cerebrum, little MT-1 protein was detected at 10 and 24 h, and there were no peaks of MT-2 protein in the cerebrum. In conclusion, MT-1 and MT-3 mRNAs but not MT-2 mRNA are easily expressed in the cerebellum rather than in the cerebrum by the injection of low-dose thimerosal. It is thought that the cerebellum is a sensitive organ against thimerosal. As a result of the present findings, in combination with the brain pathology observed in patients diagnosed with autism, the present study helps to support the possible biological plausibility for how low-dose exposure to mercury from thimerosal-containing vaccines may be associated with autism.     

Unique cellular effect of the herbicide bromoxynil revealed by electrophysiological studies using characean cells

In a previous paper, we proposed that the primary action of the herbicide bromoxynil (BX; 3,5-dibromo-4-hydroxybenzonitrile) is cytosol acidification, based on the fact that bromoxynil induced the inhibition of cytoplasmic streaming and cell death of Chara corallina in acidic external medium (Morimoto and Shimmen in J Plant Res 121:227–233, 2008). In the present study, electrophysiological analysis of the BX effect was carried out in internodal cells of C. corallina. Upon addition of BX, a large and rapid pH-dependent depolarization was induced, supporting our hypothesis. Ioxynil, which belongs to the same group as bromoxynil, also induced a large and rapid membrane depolarization in a pH-dependent manner. On the other hand, four herbicides belonging to other groups of herbicides did not induce such a membrane depolarization. Thus, BX has a unique cellular effect. The decrease in the electro-chemical potential gradient for H⁺ across the plasma membrane appears to result in inhibition of cell growth and disturbance of intracellular homeostasis in the presence of BX.     

Multiple bond-conjugated photoinduced nitric oxide releaser working with two-photon excitation

Four novel nitric oxide (NO) releasers working via two-photon excitation (TPE), based on an acceptor–donor–acceptor (A–D–A) molecular design, were synthesized. Their decomposition and NO release in response to one-photon excitation, and their decomposition in response to two-photon excitation were examined. Their photoinduced decomposition characteristics are discussed.     

Divergence pattern of animal gene families and relationship with the Cambrian explosion

There are many gene families that are specific to multicellular animals. These have either diverged from ancestral genes that are shared with fungi and/or plants or evolved from an ancestral gene unique to animals. The evolution of gene families involved in cell–cell communication and developmental control has been studied to establish whether the number of member genes increased dramatically immediately prior to or in concert with the Cambrian explosion. A molecular phylogeny‐based analysis of several animal‐specific gene families has revealed that gene diversification by duplication occurred during two active periods interrupted by a long intervening quiescent period. Intriguingly, the Cambrian explosion is situated in the silent period, indicating that there is no direct link between the first burst of gene diversification and the Cambrian explosion itself. The importance of gene recruitment as a possible molecular mechanism for morphological diversity, and its possible role for the Cambrian explosion, are discussed. BioEssays 23:1018–1027, 2001. © 2001 John Wiley & Sons, Inc.