Two of these or two of those?

Symmetrically dividing neuroepithelial cells may produce two daughters that are both proliferating or both postmitotic, as highlighted by Zigman et al. in this issue of Neuron and Sanada and Tsai in a recent issue of Cell. Here, I will attempt to offer a simple explanation why these results may be so different.     

Biocœnotic studies on the parasites of two fir-and two oak-tortricids

Zusammenfassung Innerhalb eines Mischwaldbestandes der Vogesen wurde 1956 die Parasitierung der TortricidenChoristoneura (Cacoecia) murinana,Hb.,Eucosma (Semasia) rufimitrana H.s.,Archips (Cacoecia xylosteana l. undTortrix viridana l. vergleichend untersucht. Die innerhalb eines Parasitenkreises beobachteten Konkurrenzerscheinungen und die zwischender vier bearbeiteten Parasitenkomplexen gefundenen Wechselbeziehungen wurden qualitativ und quantitativ dargestellt (Abb. 2 und 3). Zwischen der theoretisch erwarteten Wirtswahl der untersuchten polyphagen Parasiten und den im Freiland beobachteten Verh?ltnissen ergab sich ein betr?chtlicher Unterschied. Die bei der Mehrzahl der gezüchteten Parasitenarten vorhandene potentielle Polyphagie kam zwar in der Erscheinung zum Ausdruck, dass hier vielfach 2 oder 3 der 4 geprüften Wirtsarten gleichzeitig befallen worden waren, aber das Schwergewicht der Parasitierung richtete sich immer nur gegen eine Wirtsart, obwohl eine ?r?umliche und zeitliche Koinzidenz? zwischen Wirt und Parasit (Thalenhorst 1951) auch in weiteren F?llen gegeben gewesen w?re. Eine solche beschr?nkte Wirtswahl kann, wie die durch Freilandversuche an der IchneumonideApechthis rufata gmel. gewonnenen Ergebnisse zeigen, durch einseitiges Anfliegen bestimmter Futterpflanzen der Wirte veranlasst sein. Der Vergleich zwischen der Wirtswahl in verschiedenen Beobachtungsgebieten weist schliesslich darauf hin, dass das Verhalten im Freiland bei manchen Parasitenarten weitgehen unberechenbar ist. Neben der Lebensweise der untersuchten Wirtsarten war auch die Hyperparasitierung für das Ausmass der durch die Parasiten verursachten Wirtsmortalit?t von Bedeutung. W?hrend die aus der Bioz?nose stammende HyperparasitengarniturC. murinana und die beiden Eichentortriciden in etwa gleichem Grad befield, wurde bei dem erstgenannten Wirt noch eine schwerezus?tzliche Beeinflussung der Larvenparasiten-Gruppe von seiten einiger, auch prim?r wirksamer Puppenparasiten festgestellt (Abb. 2). Diese Konkurrenzerscheinungen innerhalb des Parasitenkreises dürfte weitgehend für die Tatsache verantwortlich sein, dass beiC. murinana — im Gegensatz zu den Verh?ltnissen beiT. viridana undA. xylosteana — die Larvenparasitierung wesentlich unbedeutender ist als die Puppenparasitierung.      

Characterization of two β-glucosidase genes fromClostridium thermocellum

Summary Two -glucosidase genes, designatedbglA andbglB, were isolated from a gene bank ofClostridium thermocellum DSM 1237. The coding sequences forbglA andbglB were located on non-homologous DNA fragments of 3.2– and 3.4-kb, respectively. Both genes direct inEscherichia coli the synthesis of cytoplasmic -glucosidases, which differ with respect to substrate specificity and temperature profile. The properties of thebglA-encoded -glucosidase A closely resemble that of a -glucosidase previously isolated fromC. thermocellum cultures.     

Evolution of cooperation: two for one?

How can cooperation thrive in a selfish world? Recent evolution experiments show how bacteria themselves can generate conditions that make cooperation a winning strategy. At least in the short term.     

Semi-β-carotenone from leaves of two cycads

A rare secocarotenoid, semi-β-carotenone, has been isolated from young leaves of Ceratozamia fuscoviridis (a form of C. mexicana Brongn.) and of C. kuesteriana. This is the first time that this carotenoid has been obtained from photosynthetic tissue. New data on the chromatographic behaviour and on the spectroscopic properties of the carotenoid are presented.     

Sedimentation-equilibrium studies on the heterogeneity of two β-lactamases

Solutions of crystalline beta-lactamase I and beta-lactamase II, prepared by Kuwabara (1970), were examined in the ultracentrifuge and their sedimentation coefficients, diffusion coefficients, molecular weights and heterogeneity determined. Each sample was shown to consist of a major component comprising at least 97% of the material and a minor component of much higher molecular weight. The molecular weights of the major components were 27800 for beta-lactamase I and 35600 for beta-lactamase II. Emphasis is placed on a straightforward practical way of analysing the sedimentation-equilibrium results on mixtures of two macromolecular components rather than on a strict theoretical solution. Appendices describe the theory of systems at both chemical and sedimentation equilibrium and the procedure for calculating the combined distribution of two components.     

Consolidation and reconsolidation: two lives of memories?

Most studies on memory consolidation consider the new information as if it were imposed on a tabula rasa, but considerable evidence indicates that new memories must be interleaved within a large network of relevant pre-existing knowledge. Early studies on reconsolidation highlighted that a newly consolidated memory could be erased after reactivation, but new evidence has shown that an effective reactivation experience must also involve memory reorganization to incorporate new learning. The combination of these observations on consolidation and reconsolidation highlights the fundamental similarities of both phenomena as the integration of new information and old, and it suggests reconsolidation = consolidation as a neverending process of schema modification.     

Physical properties of detergent-based aqueous two–phase systems

The physical behavior of the binary phase systems of the non-ionic polyoxyethylene detergent Agrimul NRE 1205 and water was investigated. This technical detergent can be used for the large-scale recovery of biomolecules in detergent based aqueous two-phase systems. The phase diagram was determined. It shows significant and unexpected differences to highly purified detergents. Very similar to neat detergents the phase diagram can be influenced by auxiliary chemicals thus shifting the entire phase diagram in general to lower temperatures. This was demonstrated by lowering the cloud-point by various additions. The concentration factor, as an important parameter of a first capture step in purification was investigated and modeled. Auxiliary chemicals, temperature change and change in detergent concentration also influence the viscosity and density of the phases. These experimental data are shown. They can help to explain the separation behavior of proteins. In large-scale separations aqueous two-phase systems are separated using disc-stack centrifuges. It is demonstrated that this is not a feasible method for detergent-based aqueous two-phase extraction and the physical reason is presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

A comparison of two fouling‐resistant heat exchangers

Fouling cannot always be prevented; it is important to consider the design of fouling‐resistant heat exchangers. To examine these exchangers, a test fluid whose fouling behaviour is understood should be used. Experiments have been conducted to examine the response of two model systems, a pulsatile flow and a fluid bed heat exchanger, to fouling from whey protein concentrates. Both systems are effective in certain cases, although the enhanced mass transfer possible in the pulsatile flow exchanger can increase fouling when mass transfer controls deposition. This demonstrates the possible danger in installing “antifouling”; systems. The possible mechanisms by which antifouling exchangers operate is discussed; they may work both by slowing the kinetics of fouling or enhancing the heat transfer coefficient. A simple model to demonstrate the design of antifouling exchangers is presented.     

Ia antigens contain two distinct forms of β chain

Two new forms of chain, ₁ and ₂, in I-A immunoprecipitates are described, which differ in their migration values in SDS-PAGE under nonreducing conditions, but which migrate identically in a reduced form. This behavior is very likely due to a different arrangement of intramolecular disulfide bonds which may influence mobility in SDS-PAGE. Peptide map analysis confirmed that ₁ and ₂, possess identical primary polypeptide structures. These two forms of chain are also expressed on the cell surface and it is suggested that both associate with chains. The structural differences in these complexes may lead to an increase in heterogeneity of la antigens which could be of importance for T-cell recognition.     

Prevalence and phylogenetic relationship of two β-carbonic anhydrases in affiliates of Enterobacteriaceae

Enterobacteriaceae, one of the major families of microorganisms that inhabit the soil and gut, internally regulate constant fluctuations in soil and gut pH by buffering these changes through the presence of carbonic anhydrase (CA). In our study, we prove the prevalence of β-CA, derived from the can gene, in members of Enterobacteriaceae by using a combination of experimental and bioinformatics approaches. Enzyme purification and western blot analysis revealed the presence of β-CA in Enterobacter sp. RS1. Genetic studies confirmed the presence of β-CA in both Enterobacter sp. RS1 and Citrobacter freundii SW3. Our analysis of the divergence of cynT and can genes among harboring members indicated that the can gene was more prominent in Enterobacteriaceae than cynT. Sequence analysis of the can gene revealed a >25 % similarity among all sequences and a >50 % similarity among sequences from the Enterobacteriaceae family. The β-CA from C. freundii SW3 and Enterobacter sp. RS1, isolated from soil and used in this study, possessed a high similarity with the can gene. The close association among Enterobacteriaceae genera usually found in the soil and gut and the sequence similarity of β-CA in the different genera of Enterobacteriaceae suggest the importance of the can gene in oscillating environmental conditions.     

Evidence for the occurrence of two forms of β-lipotropin in rat pituitary

A peptide isolated from porcine gut according to its glucagon-like activity in liver (bioactive enteroglucagon) has been characterized immunologically, biologically and chemically: its potency relative to pancreatic glucagon in interacting with an antiglucagon antibody, hepatic glucagon-binding sites and hepatic adenylate cyclase was ～100%, 20% and 10%, respectively. In contrast, it is ～20-times more potent than glucagon in oxyntic glands, justifying the term ‘oxyntomodulin’. Chemically, it consists in the 29 amino acid-peptide glucagon elongated at its C-terminal end by the octapeptide Lys—Arg—Asn—Lys—Asn—Asn—Ile &;—Ala; accordingly, it is called ‘glucagon-37’     

Construction and characterization of two versions of bifunctional EGFP–sTRAIL fusion proteins

The extracellular portion (amino acids 95–281 or 114–281) of the human tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) was genetically linked to the C terminus of the fluoresce-enhanced green fluorescent protein variant (EGFP) to generate two versions of EGFP–sTRAIL fusion proteins, designated EGFP–sTR95 and EGFP–sTR114, respectively. The two versions of EGFP–sTRAIL fusion proteins both induce extensive apoptosis in lymphoid as well as nonlymphoid tumor cell lines. In addition, the two versions of fusion proteins retain similar fluorescence spectra to those of EGFP and have shown the specific binding to TRAIL receptor-positive cells; thus, the stained cells could be analyzed with flow cytometry. Hence, the two versions of fusion proteins represent a readily obtainable source of biologically active sTRAIL that may prove useful in exploit fully the characteristics of both the soluble TRAIL and its receptor system.     

Stigma development and receptivity of two Kalanchoë blossfeldiana cultivars

Several members of the Kalanchoë genus are popular as ornamental plants. Cross-breeding and wide hybridisation are essential to continuously introduce novel traits into cultivated plant material. This study aimed to identify the major factors related to the stigma affecting cross-pollination in the Kalanchoë blossfeldiana. Pollen tube growth after pollination of K. blossfeldiana ‘Jackie’ and ‘Reese’ was examined at different stigma developmental stages. Five distinct developmental stages were identified based on changes in morphology and activity of stigmatic peroxidase. After reciprocal pollination at the five stigma developmental stages, fluorescence microscopy was used to estimate the number of pollen tubes in situ. Both cultivars had receptive stigmas from stage I to IV, which concurred with the continuous expansion of the stigma covered with exudates. No pollen tube growth was observed at stage V for both cultivars. The number of pollen tubes was significantly higher in carpels pollinated at stage III, characterized by loose arrangement of the papillae and maximal amount of exudates, compared to all other developmental stages. Stigmas showing drying exudates and absence of peroxidase exhibited a relatively decreased number of pollen tubes in situ. No pollen tubes germinated on wilting stigmas. The arrangement of the papillae, the presence of exudates and peroxidase activity affected the number of pollen tubes in cross-pollination of K. blossfeldiana cultivars ‘Jackie’ and ‘Reese’. These results will help breeders to better select the optimal time for effective pollination. The findings may be applicable for other cultivars of K. blossfeldiana and relevant for different species of Kalanchoë.     

Characterization of β2-microglobulin transcripts from two teleost species

Using degenerate primers based on published ₂-microglobulin sequences we were able to obtain an expected 111 base pairs (bp) polymerase chain reaction (PCR) fragment from tilapia genomic DNA. The sequence of this fragment showed a high degree of similarity to mouse ₂-microglobulin at the protein level. We used these primers in an anchored PCR to obtain a 213 bp PCR fragment from a carp cDNA library. This was then used to clone a full-length ₂-microglobulin cDNA from carp. The carp sequence showed the highest similarity to rabbit ₂-microglobulin. Both sequences showed strong similarities to all previously published vertebrate ₂-microglobulin sequences. The predicted protein secondary structure of both the carp and tilapia clones was almost identical to the corresponding regions of previously known vertebrate ₂-microglobulin protein sequences. When either the carp or tilapia probes were used against corresponding northern blots, they hybridized to a message of approximately 800–1000 bases long, which corresponds to the previously published lengths of ₂-microglobulin mRNAs. Southern blotting indicated that ₂-microglobulin was encoded by a single copy gene in both cases. Phylogenetic analysis indicated that the sequences were related to the ₂-microglobulins of higher vertebrates but grouped together in an ancestral position.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers L05536 (carp), L05537 (tilapia).     

Oxidation of arsenite by two β-proteobacteria isolated from soil

Two heterotrophic As(III)-oxidizing bacteria, SPB-24 and SPB-31 were isolated from garden soil. Based on 16S rRNA gene sequence analysis, strain SPB-24 was closely related to genus Bordetella, and strain SPB-31 was most closely related to genus Achromobacter. Both strains exhibited high As(III) (15 mM for SPB-24 and 40 mM for SPB-31) and As(V) (>300 mM for both strains) resistance. Both strains oxidized 5 mM As(III) in minimal medium with oxidation rate of 554 and 558 μM h⁻¹ for SPB-24 and SPB-31, respectively. Washed cells of both strains oxidized As(III) over broad pH and temperature range with optimum pH 6 and temperature 42°C for both strains. The As(III) oxidation kinetic by washed cells showed K _m and V _max values of 41.7 μM and 1,166 μM h⁻¹ for SPB-24, 52 μM and 1,186 μM h⁻¹ for SPB-31. In the presence of minimal amount of carbon source, the strains showed high As(III) oxidation rate and high specific arsenite oxidase activity. The ability of strains to resist high concentration of arsenic and oxidize As(III) with highest rates reported so far makes them potential candidates for bioremediation of arsenic-contaminated environment.