Clonal Analysis of Cell Division in the Bacillus subtilis div IV-B1 Minicell-Producing Mutant

Spores of the Bacillus subtilis minicell-producing mutant div IV-B1 were germinated and grown to microcolonies in chambers which facilitate continuous observation of the developing clones with a phase-contrast microscope. Time lapse photographs were taken of 46 clones, covering the period from the beginning of outgrowth until at least two rounds of cell division had been completed. Cell lineages were constructed from contour length measurements of the photographs. These data include cell lengths, division site locations, and cell numbers in clones of various ages. From these data we have determined that the probability of a minicell being produced at any division by the div IV-B1 mutant is 0.31. The location of the abnormal division site which generates the first minicell produced in the outgrowing clone appears to be random with respect to the existing cell poles. In contrast, the location of the second abnormal division site, and hence the second minicell, is not random but rather occurs preferentially in proximity to the first minicell. This clustering of abnormal events suggests that division site location is related to pole age (generations), although other influences on minicell clustering cannot be ruled out at present.     

Improving Phenotypic Prediction by Combining Genetic and Epigenetic Associations

We tested whether DNA-methylation profiles account for inter-individual variation in body mass index (BMI) and height and whether they predict these phenotypes over and above genetic factors. Genetic predictors were derived from published summary results from the largest genome-wide association studies on BMI (n ∼ 350,000) and height (n ∼ 250,000) to date. We derived methylation predictors by estimating probe-trait effects in discovery samples and tested them in external samples. Methylation profiles associated with BMI in older individuals from the Lothian Birth Cohorts (LBCs, n = 1,366) explained 4.9% of the variation in BMI in Dutch adults from the LifeLines DEEP study (n = 750) but did not account for any BMI variation in adolescents from the Brisbane Systems Genetic Study (BSGS, n = 403). Methylation profiles based on the Dutch sample explained 4.9% and 3.6% of the variation in BMI in the LBCs and BSGS, respectively. Methylation profiles predicted BMI independently of genetic profiles in an additive manner: 7%, 8%, and 14% of variance of BMI in the LBCs were explained by the methylation predictor, the genetic predictor, and a model containing both, respectively. The corresponding percentages for LifeLines DEEP were 5%, 9%, and 13%, respectively, suggesting that the methylation profiles represent environmental effects. The differential effects of the BMI methylation profiles by age support previous observations of age modulation of genetic contributions. In contrast, methylation profiles accounted for almost no variation in height, consistent with a mainly genetic contribution to inter-individual variation. The BMI results suggest that combining genetic and epigenetic information might have greater utility for complex-trait prediction.     

The (mis)concept of species recognition

To many, the concept of 'species recognition' is integral to the origin and maintenance of species. However, the heuristic value of species recognition is hampered by its reliance on the problematic concept of species. In this paper, we first discuss assumptions associated with prevailing use of the term, including the typological implications of the concept, the false dichotomy of compatibility and mate quality, and the commonly held model of species recognition in which animals determine taxonomic status before mate status. Subsequently, we propose research directions aimed to improve our understanding of the role of courtship behavior in speciation. We propose two complementary research approaches, one addressing the processes that drive the evolution of mate recognition systems and the other addressing the phenotypic architecture of behavioral isolation. Our approach emphasizes the fitness consequences and multidimensional nature of mate choice.     

Characterization of the hypnotic effects of triazolam microinjections into the medial preoptic area.

We have previously reported that microinjections of the benzodiazepine hypnotic triazolam into the medial preoptic area (MPA) of the hypothalamus enhance sleep in rats. The present study further characterizes this effect, by examining its anatomical specificity, determining whether it is mediated by interaction with central benzodiazepine receptors, and assessing whether sleep induction is associated with changes in core temperature. It was found that microinjections of 0.25 and 0.5 micrograms triazolam into two nearby structures, the lateral preoptic area and diagonal band of Broca, failed to alter sleep. Total sleep time was enhanced by microinjection of triazolam into the MPA, and this effect was blocked by co-administration of the benzodiazepine receptor blocker RO 15-1788. Sleep enhancement by triazolam was not associated with significant alterations in core body temperature. These observations continue to suggest that the MPA may be a site which mediates the hypnotic effect of triazolam, and add to the growing body of data emphasizing the importance of hypothalamic function in the regulation of sleep and waking.     

Experience with the deltopectoral flap.

The deltopectoral flap is a most versatile source of skin coverage or mucosal lining (or both). There is remarkable safety in the use of this flap in relation to its size, and there is only limited need for delay--because it pedicle is an axial flap. Nonetheless, the terminal part requires the attention to detail which any random flap requires--such as the avoidance of hematoma and infection and the prevention of tension, kinking, and angulation. This not only will ensure the safety of the flap, but also will prevent the rather common and annoying minor complications that delay the patient's convalescence.     

Amphibian Declines in Latin America: Widespread Population Declines,Extinctions, and Impacts1

Amphibian populations are in decline throughout Latin America; all families of frogs have experienced declines, but the species associated with aquatic habitats in upland areas have been most affected. Declines in Latin America were most common during the 1980s, but new declines continue to be reported. The causes of declines are varied, but they have most often been associated with habitat loss, a pathogenic fungus, and climate change. Scientists are just beginning to grasp the ethical and biological implications of losses of this magnitude. In this Special Section, we provide a general summary of the phenomenon and introduce five contributed papers that provide new data and new insights into Latin American declines.     

The effect of caffeine on repair systems in oocytes of Drosophila melanogaster. I

Young Drosophila females were treated with caffeine, then mated for 24 h to males that had been irradiated with 2000 R X-irradiation, so that only mature spermatozoa were sampled. The radiation-induced frequency of dominant lethals and sex chromosome loss in the paternal genome was determined. The results show that treatment of females with caffeine leads to an increase in the frequencies of radiation-induced dominant lethals and to sex-chromosome loss.When young virgin females of the radioresistant stock RöI₂ were treated with caffeine and then irradiated with 3000 R X-irradiation, a striking increasein dominant lethals (in the maternal genome) was observed; caffeine treatment increased the X-ray response of the radioresistant stock to the level of the normal (+60) stock. It is suggested that caffeine reduces the efficiency of a system in Drosophila oocytes that repairs X-ray-produced chromosome breaks in both the paternal and maternal genomes.     

Minicells of Bacillus subtilis: a New Bacteriophage-Blocking Agent

Bacteriophage SP01, SP17, and phi29 rapidly absorb irreversibly to minicells of Bacillus subtilis but do not produce a lytic cycle in minicells.