First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

INDIVIDUALITY IN THE VOICE OF FUR SEAL FEMALES: AN ANALYSIS STUDY OF THE PUP ATTRACTION CALL IN ARCTOCEPHALUS TROPICALIS

Like most otariids species, the Subantarctic fur seal breeds on land in large, dense colonies. Pups are confronted by the long and repetitive absences of their mother throughout lactation. At each mother's return, pups have to find her among several hundreds of congeners. This recognition process mainly relies on acoustic signals. We performed an acoustic analysis on 125 calls from 20 females recorded during the 1999–2000 breeding season on Amsterdam Island (Indian Ocean). Ten variables were measured in both temporal and frequency domains. To find the acoustic parameters supporting individual signature, we assessed the differences between individuals using Kruskall-Wallis univariate analysis of variance. For each variable, we also calculated the potential of individuality coding (PIC) as the ratio between the between-individual coefficient of variation and the mean value of the within-individual coefficients of variation. We found that the frequency spectrum, the characteristics of the frequency modulation of the initial and middle part of the call and the call duration exhibit an important individual stereotypy (PIC values ranging between 1.5 and 3), whereas features relative to amplitude and the frequency modulation of the final part of the call are weakly individualized (PIC values between 1 and 1.2).     

Characterization of an Escherichia coli mutant, feeA, displaying resistance to the calmodulin inhibitor 48/80 and reduced expression of the rare tRNA3Leu

We previously described a mutation feeB1 conferring a temperature-sensitive filamentation phenotype and resistance to the calmodulin inhibitor 48/80 in Escherichia coli, which constitutes a single base change in the acceptor stem of the rare tRNA₃^Leu recognizing CUA codons. We now describe a second mutant, feeA1, unlinked to feeB, but displaying a similar phenotype, 48/80 resistance and a reduced growth rate at the permissive temperature, 30°C, and temperature-sensitive, forming short filaments at 42°C. In the feeA mutant, tRNA₃^Leu expression (but not that of tRNA₁^Leu) was reduced approximately fivefold relative to the wild type. We previously showed that the synthesis of β-galactosidase, which unusually requires the translation of 6-CUA codons, was substantially reduced, particularly at 42°C, in feeB mutants. The feeA mutant also shows drastically reduced synthesis of β-galactosidase at the non-permissive temperature and reduced levels even at the permissive temperature. We also show that increased copy numbers of the abundant tRNA₁^Leu, which can also read CUA codons at low efficiency, suppressed the effects of feeA1 under some conditions, providing further evidence that the mutant was deficient in CUA translation. This, and the previous study, demonstrates that mutations which either reduce the activity of tRNA₃^Leu or the cellular amount of tRNA₃^Leu confer resistance to the drug 48/80, with concomitant inhibition of cell division at 42°C.     

The highly thermostable arginine repressor of Bacillus stearothermophilus: gene cloning and repressor–operator interactions

We report here the cloning of the arginine repressor gene argR of Bacillus stearothermophilus and the characterization and purification to homogeneity of its product. The deduced amino acid sequence of the 16.8-kDa ArgR subunit shares 72% identity with its mesophilic homologue AhrC of Bacilus subtilis . Sequence analysis of B. stearothermophilus ArgR and comparisons with mesophilic arginine repressors suggest that the thermostable repressor comprises an N-terminal DNA-binding and a C-terminal oligomerization and arginine-binding region. B. stearothermophilus ArgR has been overexpressed in E. coli and purified as a 48.0-kDa trimeric protein. The repressor inhibits the expression of a B. stearothermophilus argC–lacZ fusion in E. coli cells. In the presence of arginine, the purified protein binds tightly and specifically to the argC operator, which largely overlaps the argC promoter. The purified B. stearothermophilus repressor proved to be very thermostable with a half-life of approximately 30 min at 90°C, whereas B. subtilis AhrC was largely inactivated at 65°C. Moreover, ArgR operator complexes were found to be remarkably thermostable and could be formed efficiently at up to 85°C, well above the optimal growth temperature of the moderate thermophile B. stearothermophilus . This pronounced resistance of the repressor–operator complexes to heat treatment suggests that the same type of regulatory mechanism could operate in extreme thermophiles.     

The stationary state of epithelia

A tissue is a geometrical, space-filling, random cellular network; it remains in this steady state while individual cells divide. Cell division is a local, elementary topological transformation which establishes statistical equilibrium of the structure. We describe the physical conditions to maintain stationary the epidermis (of mammals or of the cucumber), in spite of the fact that cells constantly divide and die. Specifically, we study the statistical equilibrium of the basal layer, a corrugated surface filled with cells, constituting a two-dimensional topological froth. Cells divide and detach from the basal layer, and these two topological transformations are responsible for the stationary state of the epidermis. The topological froth is capable of responding rapidly and locally to external constraints, and is a good illustration of the plasticity of random cellular networks.Statistical equilibrium is controlled by entropy, both as a measure of disorder and as information, and is characterized by observable relations between average cell shapes and sizes. The technique can be applied to any random cellular network in dynamical equilibrium. Mitosis as the dominating topological transformation and the fact that the distribution of cell shapes is very narrow are the only inputs specific to biology.

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Resume Un tissu est, à première vue, un pavage aléatoire d'une surface ou d'un volume par des polygones (polyèdres) topologiques, les cellules. Ce pavage reste dans un état stationnaire alors que les cellules se divisent constamment. Nous décrivons les conditions physiques nécessaires à l'état stationnaire de l'épiderme (des mammifères et du concombre), en dépit du fait que ses cellules se divisent et meurent. En particulier, nous étudions l'équilibre statistique de la couche basale, une surface couverte de cellules constituant une mousse topologique aléatoire. Les cellules se divisent et se détachent de la couche basale, et ces transformations topologiques sont responsable de l'état stationnaire de l'épiderme. Cette mousse topologique est capable de répondre rapidement et localement à des contraintes externes. C'est un exemple de plasticité de structures cellulaires aléatoires.L'équilibre statistique est contrôlé par l'entropie qui est ici à la fois une mesure du désordre et une quantité d'information. Il est caractérisé par des relations facilement observables entre les formes des cellules et leurs dimensions. Les seuls éléments spécifiques aux tissus biologiques sont la mitose comme transformation topologique dominante, et l'étroitesse de la distribution des formes de cellules.

     

Posterior dental size reduction in hominids: The Atapuerca evidence

In order to reassess previous hypotheses concerning dental size reduction of the posterior teeth during Pleistocene human evolution, current fossil dental evidence is examined. This evidence includes the large sample of hominid teeth found in recent excavations (1984–1993) in the Sima de los Huesos Middle Pleistocene cave site of the Sierra de Atapuerca (Burgos, Spain). The lower fourth premolars and molars of the Atapuerca hominids, probably older than 300 Kyr, have dimensions similar to those of modern humans. Further, these hominids share the derived state of other features of the posterior teeth with modern humans, such as a similar relative molar size and frequent absence of the hypoconulid, thus suggesting a possible case of parallelism. We believe that dietary changes allowed size reduction of the posterior teeth during the Middle Pleistocene, and the present evidence suggests that the selective pressures that operated on the size variability of these teeth were less restrictive than what is assumed by previous models of dental reduction. Thus, the causal relationship between tooth size decrease and changes in food-preparation techniques during the Pleistocene should be reconsidered. Moreover, the present evidence indicates that the differential reduction of the molars cannot be explained in terms of restriction of available growth space. The molar crown area measurements of a modern human sample were also investigated. The results of this study, as well as previous similar analyses, suggest that a decrease of the rate of cell proliferation, which affected the later-forming crown regions to a greater extent, may be the biological process responsible for the general and differential dental size reduction that occurred during human evolution. © 1995 Wiley-Liss, Inc.     

In vitro colonization ability of human colon mucosa by exogenous Lactobacillus strains

Abstract A 5.4 kb Hind III DNA fragment carrying the gene encoding raw starch-digesting α-amylase (RSDA), has been previously cloned from Bacillus circulans F-2 and expressed in Escherichia coli [Kim et al. (1990) Biochim. Biophys. Acta 1048, 2233–2238]. Interestingly, when the cell extract of E. coli harboring a plasmid carrying this fragment was incubated with l M NaCl, it exhibited about 10 times higher enzyme activity than when assayed without NaCl. Differential zymograms showed two different amylase activities: one for RSDA and the other for a salt-dependent a-amylase (SDA). Even though RSDA activity was detected without NaCl, SDA activity was detected only in high concentrations of NaCl. SDA activity was fully detected at above l M NaCl. Results from subcloning of the genes, fractionation analysis of cell extracts, and immunological assays clearly suggested that the two amylases are genetically distinct and that genes for both enzymes are closely linked on the 5.4 kb DNA fragment.     

Mapping the diabetes polygene Idd3 on mouse Chromosome 3 by use of novel congenic strains

Development of novel congenic mouse strains has allowed us to better define the location of the diabetogenic locus, Idd3, on Chromosome (Chr) 3. Congenic strains were identified by use of published and newly developed microsatellite markers, their genomes fingerprinted by a rapid, fluorescence-based approach, and their susceptibility to type 1 diabetes evaluated. The maximum interval containing Idd3 is now approximately 4 cM.