Genetical and biochemical comparisons of alcohol dehydrogenase isozymes from Anastrepha fraterculus and A. obliqua (Diptera: Tephritidae): Evidence for gene duplication

The electrophoretic patterns of the enzyme alcohol dehydrogenase (ADH) from Anastrepha fraterculus and A. obliqua were studied. Two loci were found to code for the enzyme in A. fraterculus, and three in A. obliqua. In both species, all isozymes were active in third-instar larvae. A cationic isozyme (Adh-1) was active mainly in the visceral fat body of both species. In A. fraterculus, the locus had an anionic polymorphic isozyme (Adh-3) that was detected in the parietal fat body. In addition to these two loci, a third locus for an anionic isozyme (Adh-2), which was active in the digestive tube of larvae, was present in A. obliqua and probably resulted from gene duplication. For both species, multiple forms of the isozymes are formed by binding of an NAD-carbonyl compound, as in Drosophila melanogaster. Both larvae and early pupae of A. obliqua had almost twice the specific ADH activity as A. fraterculus. The ethanol content of the host fruit infested with A. obliqua (red mombim) was also higher than that of the host fruit infested with A. fraterculus (guava).This research was supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnologico (CNPq-PIG 40.2486/82).     

Der cytologische Nachweis von doppelter Restitution beiFragaria

Double restitution has been observed cytologically for the first time in microsporogenesis of a F₁ hybridFragaria virginiana ×F. chiloensis . Restitution is probably due to irregularities affecting the spindle mechanism. Single or double restitution may depend upon the duration of the effect or upon the stage of meiosis affected. The occurrence of triades is indicative of a possible intracellular diversity. Although the reason which may cause restitution remains to be ascertained, maternal inheritance indicates an extrachromosomal cause.

     

Molecular and cytological characteristics of nuclear DNA and chromatin for angiosperm systematics: DNA diversification in the evolution of four orchids

The species- and genus-specific DNA content, average base composition of nuclear DNA, presence or absence of satellite DNA, the percentage of heterochromatin and other characteristics of nuclear DNA and nuclear structure allow to deduce the molecular changes which accompanied, or more probably caused, cladogenesis in the orchids studied. It is suggested that saltatory replication (generative amplification) of certain DNA sequenes, diversification of reiterated DNA sequences, and loss of DNA play an important role in the evolution of orchids.—The relationship between changes of genome composition and of nuclear structure and ultrastructure is discussed on the basis of cot curves, heterochromatin staining with Giemsa (C banding), electron microscopy of nuclei, and molecular hybridization in situ.Some aspects of this paper have been presented at the Helsinki Chromosome Conference, August 1977 (Nagl & Capesius 1977).     

Bahavioral fever in crayfish

Crayfish (Cambarus bartoni) were tested individually in an electronic shuttlebox thermoregulatory device which allowed them to control water temperature, and thereby their body temperature, by their movements.Crayfish which initially selected 22.1°C water increased their preferred temperature by 1.8°C following injection of killed bacteria (Aeromonas hydrophila) into the gill cavity.This behavioral fever appears similar to that of vertebrates, and may enhance host defense reactions against pathogens.     

Systematics and phylogeny of the Aglajidae (Opisthobranchia: Mollusca)

The generic limits within the Aglajidae are reviewed and modified, based on the study of 21 species. Navanax Pilsbry, 1895 is reinstated as a genus distinct from Aglaja. The generic placement of several species is altered from previous works. An evaluation of morphological characters suggests that each of six genera has distinctive external morphology. The systematic value of twelve characters is critically reviewed. The evolutionary relationships of the Aglajidae and its genera to other philinacean familes are discussed.     

The acetylene reduction technique as an assay for nitrogenase activity in the methane oxidizing bacterium Methylococcus capsulatus strain bath

The use of acetylene as a convenient assay substrate for nitrogenase in methane oxidising bacteria is complicated by the observation that it is a potent inhibitor of the methane monooxygenase enzyme in both whole cells and cell-free extracts. If the cells were provided with alternative oxidisable carbon substrates other than methane then nitrogen fixing cells would reduce acetylene to ethylene. Hydrogen gas also served as an oxidisable substrate in the assay. Nitrous oxide, which is reduced by nitrogenase to N₂ and H₂O, was not an inhibitor of methane monooxygenase function and could be used as a convenient assay substrate for nitrogenase. Reduction of both substrates by whole cells showed similar response to oxygen in the assay system and in this respect Methylococcus resembles other free living nitrogen fixing aerobes.     

Amelioration of Bacterial Genomes: Rates of Change and Exchange

Although bacterial species display wide variation in their overall GC contents, the genes within a particular species' genome are relatively similar in base composition. As a result, sequences that are novel to a bacterial genome—i.e., DNA introduced through recent horizontal transfer—often bear unusual sequence characteristics and can be distinguished from ancestral DNA. At the time of introgression, horizontally transferred genes reflect the base composition of the donor genome; but, over time, these sequences will ameliorate to reflect the DNA composition of the new genome because the introgressed genes are subject to the same mutational processes affecting all genes in the recipient genome. This process of amelioration is evident in a large group of genes involved in host-cell invasion by enteric bacteria and can be modeled to predict the amount of time required after transfer for foreign DNA to resemble native DNA. Furthermore, models of amelioration can be used to estimate the time of introgression of foreign genes in a chromosome. Applying this approach to a 1.43-megabase continuous sequence, we have calculated that the entire Escherichia coli chromosome contains more than 600 kb of horizontally transferred, protein-coding DNA. Estimates of amelioration times indicate that this DNA has accumulated at a rate of 31 kb per million years, which is on the order of the amount of variant DNA introduced by point mutations. This rate predicts that the E. coli and Salmonella enterica lineages have each gained and lost more than 3 megabases of novel DNA since their divergence. Received: 7 July 1996 / Accepted: 27 September 1996     

Retroviral Oligonucleotide Distributions Correlate with Biased Nucleotide Compositions of Retrovirus Sequences,Suggesting a Duplicative Stepwise Molecular Evolution

A computer-assisted analysis was made of 24 complete nucleotide sequences selected from the vertebrate retroviruses to represent the ten viral groups. The conclusions of this analysis extend and strengthen the previously made hypothesis on the Moloney murine leukemia virus: The evolution of the nucleotide sequence appears to have occurred mainly through at least three overlapping levels of duplication: (1) The distributions of overrepresented (3–6)-mers are consistent with the universal rule of a trend toward TG/CT excess and with the persistence of a certain degree of symmetry between the two strands of DNA. This suggests one or several original tandemly repeated sequences and some inverted duplications. (2) The existence of two general core consensuses at the level of these (3–6)-mers supports the hypothesis of a common evolutionary origin of vertebrate retroviruses. Consensuses more specific to certain sequences are compatible with phylogenetic trees established independently. The consensuses could correspond to intermediary evolutionary stages. (3) Most of the (3–6)-mers with a significantly higher than average frequency appear to be internally repeated (with monomeric or oligomeric internal iterations) and seem to be at least partly the cause of the bias observed by other researchers at the level of retroviral nucleotide composition. They suggest a third evolutionary stage by slippage-like stepwise local duplications. Received: 3 January 1996 / Accepted: 27 March 1996     

Comparative genomic mapping between a 754 kb region flanking DREB1A in Arabidopsis thaliana and maize

Comparative mapping between model plant species for which the complete genome sequence is known and crop species has been suggested as a new strategy for the isolation of agronomically valuable genes. In this study, we tested whether comparative mapping between Arabidopsisand maize of a small region (754 kb) surrounding the DREB1A gene in Arabidopsis could lead to the identification of an orthologous region in maize containing the DREB1A homologue. The genomic sequence information available for Arabidopsis allowed for the selection of conserved, low-copy genes that were used for the identification of maize homologues in a large EST database. In total, 17 maize homologues were mapped. A second BLAST comparison of these genes to the recently completed Arabidopsis sequence revealed that 15 homologues are likely to be orthologous as the highest similarity score was obtained either with the original Arabidopsis gene or with a highly similar Arabidopsis gene localized on a duplication of the investigated region on chromosome 5. The map position of these genes showed a significant degree of orthology with the Arabidopsis region. Nevertheless, extensive duplications and rearrangements in the Arabidopsisand maize genomes as well as the evolutionary distance between Arabidopsis and maize make it unlikely that orthology and collinearity between these two species are sufficient to aid gene prediction and cloning in maize.     

Myoblast proliferation and syncytial fusion both depend on connexin43 function in transfected skeletal muscle primary cultures

Muscles are formed by fusion of individual postmitotic myoblasts to form multinucleated syncytial myotubes. The process requires a well-coordinated transition from proliferation, through migratory alignment and cycle exit, to breakdown of apposed membranes. Connexin43 protein and cell-cycle inhibitor levels are correlated, and gap junction blockers can delay muscle regeneration, so a coordinating role for gap junctions has been proposed. Here, wild-type and dominant-negative connexin43 variants (wtCx43, dnCx43) were introduced into rat myoblasts in primary culture through pIRES-eGFP constructs that made transfected cells fluoresce. GFP-positive cells and vitally-stained nuclei were counted on successive days to reveal differences in proliferation, and myotubes were counted to reveal differences in fusion. Individual transfected cells were injected with Cascade Blue, which permeates gap junctions, mixed with FITC-dextran, which requires cytoplasmic continuity to enter neighbouring cells. Myoblasts transfected with wtCx43 showed more gap-junctional coupling than GFP-only controls, began fusion sooner as judged by the incidence of cytoplasmic coupling, and formed more myotubes. Myoblasts transfected with dnCx43 remained proliferative for longer than either GFP-only or wtCx43 myoblasts, showed less coupling, and underwent little fusion into myotubes. These results highlight the critical role of gap-junctional coupling in myotube formation.