Low genetic variability in a Utah cherry-infesting population of the apple maggot, Rhagoletis pomonella

The apple maggot fly, Rhagoletis pomonella (Walsh), has only recently been found in Utah infesting sour cherry, Prunus cerasus L. An electrophoretic comparison of flies from Utah cherries with flies from Illinois hawthorns, Crataegus mollis (T. & G.) Scheele (a native host within the native range of the fly), show a marked reduction of genetic variability in the Utah sample. This result is indicative of a genetic bottleneck associated with the establishment of the apple maggot population in Utah cherries.

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Résumé R. pomonella (Walsh), est originaire de Crataegus dans l'Amérique du N.E. Il attaque de nombreux autres fruits, y compris les pommes et les cerises aigres (Prunus cerasus). La mouche a été récemment signalée en Utah, à la fois sur cerises et sur Crataegus douglasii. Nous avons comparé les niveaux de variabilité génétique d'une population de l'Utah contaminant les cerises et d'une population de l'Illinois contaminant C. mollis (la population de l'Illinois est représentative des niveaux de variabilité génétique dans l'aire d'origine de la mouche).La variabilité génétique à 17 loci a été évaluée par électrophorèse sur gel d'amidon. 10 de ces loci sont polymorphes dans la population d'Illinois, mais seulement 4 dans la population de l'Utah. Les fréquences alléliques de ces 4 loci de R. pomonella diffèrent significativement en Utah et en Illinois. La population de l'Utah présente nettement moins d'allèles par locus, un plus faible pourcentage de loci polymorphes et une hétérozygotie moyenne plus faible que la population de l'Illinois. Tous ces résultats sont conformes aux conséquences prévisibles d'un goulot d'étranglement.Deux explications existent pour cette perte de variabilité, toutes les deux liées à la combinaison de la faible taille de la population et de la dérive génétique ultérieure. Pour la première, la colonisation du cerisier par les mouches venant de Crataegus peut avoir provoqué un goulot d'étranglement génétique. Au contraire, la réduction de la variabilité peut avoir été la conséquence de la colonisation de l'Utah par R. pomonella. Nous retenons cette dernière comme la cause la plus vraisemblable de la variabilité génétique de la population de R. pomonella contaminant les cerises de l'Utah.

     

Cytogenetic characterization of the L5178Y TK+/-3.7.2C mouse lymphoma cell line

The cytogenetic characterization of the L5178Y TK+/-3.7.2C mouse lymphoma cell line was carried out, utilizing G-banded metaphase chromosomes, to provide a karyotypic basis for the precise delineation of induced rearrangements in TK-/- mutants. Band-pattern measurements were used to construct ideograms which represent the position, number, size and staining intensity of the chromosome bands. The TK+/-3.7.2C cell line has been shown to provide quantitation of forward mutations induced at the autosomal thymidine kinase (TK) locus in this cell line. Chromosome analysis of the TK+/-3.7.2C cell line and derived TK-/- mutants has become important in demonstrating that the TK+/-----TK-/- assay may detect and distinguish between chromosomal events and smaller, perhaps point-mutation, events in mutant colonies.     

Clonal variations in keratin : Intermediate filament expression by human somatic cell hybrids

The intermediate filament composition of differentiated vertebrate cells provides a stable phenotype which appears to be specifically regulated in each cell type. In order to analyse the regulation of intermediate filament expression we have constructed human somatic cell hybrids from the fusion of the HeLa-derived cell line HEB7A and a normal human diploid fibroblast, GM2291. These parental cells differ with respect to the presence or absence of keratin intermediate filaments. Isolation of independently arising clones produced two classes of hybrids. One class expresses keratin in a stable manner and the other class lacks keratin altogether. Indirect immunofluorescence of hybrid cells using antikeratin antiserum demonstrates that there are variations in the intensity and organization of cytoskeletal keratin staining. SDS-PAGE comparisons of cell extracts from these hybrids indicates that there are quantitative differences in the relative amounts of individual keratin polypeptides as well. These clonal variations have allowed us to begin assessing the consequences of genetic interactions between cell types that are normally capable of closely regulating different subsets of intermediate filament genes.     

A new spring for plant cell biology: microtubules as dynamic helices

Cortical microtubules wind around plant cells describing flat, medium or steeply pitched helices. Experiments now suggest that these arrays are dynamically interconvertible — providing a spring-like device that is sensitive to environmental cues and shifts the axis of cell expansion through 90°.     

Segregation of mitochondrial DNA in human somatic cell hybrids

Summary The maintenance of mtDNA has been examined in human intraspecific hybrid cells constructed from the fusion of HEB7A, a HeLa tumor cell line carrying the mitochondrially coded chloramphenical (CAP) resistance mutation, and GM 2291, a limited lifespan human diploid fibroblast which is CAP sensitive. These two cells can be distinguished by a polymorphism in a site for the restriction endonuclease, HaeIII. Independently isolated clones of hybrid cells were characterized for their growth properties (either normal limited lifespan or transformed and immortal). Whole cell DNA preparations were made from each hybrid, digested with HaeIII, and the resultant fragments were detected by hybridization to ³²P labelled mouse mtDNA as probe. Experiments with mixtures of HEB7A and GM2291 DNA reveal that HEB7A mtDNA can be detected when it constitutes as little as 5% of the total cell mtDNA.The results indicate that the HEB7A mtDNA is lost from most hybrids, and when it does persist it is usually a minor component of total mtDNA. The addition of CAP at the time of fusion slightly increases the quantity of HEB7A mtDNA, but not enough to confer CAP resistance. Furthermore, five limited lifespan hybrids contained no detectable HEB7A mtDNA, while three transformed hybrids contained varying quantities of HEB7A mtDNA, suggesting that retention of this tumor form of mtDNA is associated with tumor growth behavior. These results suggest that cytoplasmic genetic incompatibility occurs in intraspecific hybrids.     

Antiproliferative Action of Benzodiazepines in Cultured Brain Cells Is Not Mediated Through the Peripheral-Type Benzodiazepine Acceptor

The benzodiazepines, Ro 5-4864, diazepam, clonazepam, and also PK-11195, inhibited, at micromolar concentrations, the proliferation of rat C6 glioma and mouse neuro-2A neuroblastoma cells in culture. The cells possessed high levels of "peripheral-type" high-affinity benzodiazepine binding sites as judged by binding assays and displacement potencies. However, the different potencies and specificities of compounds for the antiproliferative actions and binding affinities for the binding site suggest that the antiproliferative actions were not mediated through the peripheral-type binding site. In support of this, these compounds have also been shown to inhibit proliferation of some nonneuronal cultured cell lines, e.g., mouse SP2/O-Ag 14 hybridoma and rat NCTC epithelial cells, which have no detectable high-affinity peripheral-type benzodiazepine binding sites.     

Short-term changes in carbon-isotope discrimination identify transitions between C3 and C4 carboxylation during Crassulacean acid metabolism

Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO₂ collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO₂ exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO₂ (Phase I), discrimination () ranged from 4.4 to 6.6, equivalent to an effective carbon-isotope ratio (¹³C) of –12.3 to –14.5 versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO₂ uptake and refixation of respiratory CO₂, characteristic of CAM in the Bromeliaceae. When for the relative proportion of external (p _a ) and internal (p _i) CO₂ is taken into account, calculated p _i/p _a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of during Phase II, early in the light period, showed the transition between C₄ and C₃ pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as increased from 10.5 to 21.2 During decarboxylation in the light period (Phase III), CO₂ leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of calculated from on-line measurements (64.4) showed that the CO₂ lost was considerably enriched in ¹³C, and this was confirmed by direct analysis of the CO₂ diffusing out into a CO₂-free atmosphere ( ¹³C = + 51.6 versus PDB). Instantaneous discrimination was characteristic of the C₃ pathway during Phase IV (late in the light period), but a reduction in showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that double carboxylation involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.Abbreviations and Symbols CAM Crassulacean acid metabolism - H⁺ (dawn-dusk) variation in titratable acidity - ¹³C carbonisotope ratio of plant organic material, relative to Pee Dee Belemnite (vs. PDB) - discrimination against ¹³CO₂, - p _i, p _a internal, external partial pressures of CO₂ - Rubisco ribulose1,5-bisphosphate carboxylase - PAR photosynthetically active radiation - PEPCase phosphoenolpyruvate carboxylase We are grateful for financial support in respect of research grants (GR3/5360, GR3/6419) and a studentship awarded by the Natural Environment Research Council, UK.     

Recolonisation and recruitment of fishes to intertidal rockpools at Wellington, New Zealand

Synopsis A study of recolonisation of rockpools by intertidal fishes on the Wellington south coast, New Zealand, found the assemblage to be resilient and seasonally stable. A total of 26 species from nine families were recorded, dominated by the Tripterygiidae (triplefins) and Gobiesocidae (clingfishes). A pattern of alternating species dominance occurred, with the triplefinsBellapiscis medius andForsterygion lapillum being numerically dominant in summer, but becoming less common in winter and replaced as dominants by the clingfishesTrachelochismus pinnulatus andGastroscyphus hectoris. Juvenile recruits of eleven species occurred in the samples from spring to early summer, however only the aforementioned four species recruit to the intertidal zone in large numbers. The speed of rockpool recolonisation by fishes after extractive sampling is seasonally dependent, being quicker in the summer than winter. In general, recolonisation takes at least one month, but probably fewer than three. While stochastic factors influence assemblage composition in the short term, overall regulation of the fish assemblage of rockpools appears to be primarily deterministic, resulting in an essentially predictable taxonomic structure.