High-Resolution Sex-Specific Linkage Maps of the Mouse Reveal Polarized Distribution of Crossovers in Male Germline

Since the publication of the first comprehensive linkage map for the laboratory mouse, the architecture of recombination as a basic biological process has become amenable to investigation in mammalian model organisms. Here we take advantage of high-density genotyping and the unique pedigree structure of the incipient Collaborative Cross to investigate the roles of sex and genetic background in mammalian recombination. Our results confirm the observation that map length is longer when measured through female meiosis than through male meiosis, but we find that this difference is modified by genotype at loci on both the X chromosome and the autosomes. In addition, we report a striking concentration of crossovers in the distal ends of autosomes in male meiosis that is absent in female meiosis. The presence of this pattern in both single- and double-recombinant chromosomes, combined with the absence of a corresponding asymmetry in the distribution of double-strand breaks, indicates a regulated sequence of events specific to male meiosis that is anchored by chromosome ends. This pattern is consistent with the timing of chromosome pairing and evolutionary constraints on male recombination. Finally, we identify large regions of reduced crossover frequency that together encompass 5% of the genome. Many of these “cold regions” are enriched for segmental duplications, suggesting an inverse local correlation between recombination rate and mutation rate for large copy number variants.     

Depletion of host cell riboflavin reduces Wolbachia levels in cultured mosquito cells

Wolbachia is an obligate intracellular alphaproteobacterium that occurs in arthropod and nematode hosts. Wolbachia presumably provides a fitness benefit to its hosts, but the basis for its retention and spread in host populations remains unclear. Wolbachia genomes retain biosynthetic pathways for some vitamins, and the possibility that these vitamins benefit host cells provides a potential means of selecting for Wolbachia-infected cell lines. To explore whether riboflavin produced by Wolbachia is available to its host cell, we established that growth of uninfected C7-10 mosquito cells decreases in riboflavin-depleted culture medium. A well-studied inhibitor of riboflavin uptake, lumiflavin, further inhibits growth of uninfected C7-10 cells with an LC₅₀ of approximately 12 μg/ml. Growth of C/wStr1 mosquito cells, infected with Wolbachia from the planthopper, Laodelphax striatellus, was enhanced in medium containing low levels of lumiflavin, but Wolbachia levels decreased. Lumiflavin-enhanced growth thus resembled the improved growth that accompanies treatment with antibiotics that deplete Wolbachia, rather than a metabolic advantage provided by the Wolbachia infection. We used the polymerase chain reaction to validate the decrease in Wolbachia abundance and evaluated our results in the context of a proteomic analysis in which we detected nearly 800 wStr proteins. Our data indicate that Wolbachia converts riboflavin to FMN and FAD for its own metabolic needs, and does not provide a source of riboflavin for its host cell.     

Earth Worm: Biomass Measurement: A Science Activity for Middle School

Ridgely, Robert S. A Guide to the Birds of Panama Princeton, N.J.: Princeton University Press, 1976 394 pp., $15.00. Reviewed by Karl L. Trever

Weiner, Michael A. Man's Useful Plants New York: Macmillan Co., 1976 137 pp., $6.95. Reviewed by Carolyn M. Levin

Bendick, Jeanne How Animals Behave New York: Parents Magazine Press, 1976 64 pp., $4.96. Reviewed by Robert Deitchman

Bayne, B. L., ed. Marine Mussels: The Ecology and Physiology New York: Cambridge University Press, 1976 506 pp., $49.50. Reviewed by Brother Nicholas Sullivan

Brown, Vinson The Explorer Naturalist Harrisburg, Pa.: Stackpole Books, 1976 288 pp., $10.00. Reviewed by Paul F. Connor

Sheldon, William G. The Wilderness Home of the Giant Panda Amherst: The University of Massachusetts Press, 1975 196 pp., $12.50. Reviewed by Harold W. Puffer

Rudolph, Joachim (translated by H. C. Grinter) Chemistry for the Modern Mind New York: Macmillan Publishing Co., 1973 359 pp., $8.95. Reviewed by Donald Schwartz     

Validation of noninvasive monitoring of adrenocortical endocrine activity in ground-feeding aardwolves (Proteles cristata): exemplifying the influence of consumption of inorganic material for fecal steroid analysis

Biologically inert material in feces may confound interpretations of noninvasive fecal endocrine data, because it may induce variance related to differences in foraging behavior rather than to differences in endocrine activity. We evaluated two different enzyme immunoassays (EIAs) for the noninvasive evaluation of adrenocortical activity in ground-feeding aardwolves (Proteles cristata) and tested the influence of soil content in aardwolf feces on the interpretation of fecal glucocorticoid metabolite data. Using adrenocorticotropic hormone (ACTH) challenges for validation, we successfully identified a cortisol EIA suitable for assessing adrenocortical activity in aardwolves. An alternatively tested 11-oxoetiocholanolone EIA failed to detect a biologically relevant signal after ACTH administration. Although the proportion of inorganic content in aardwolf feces did not alter qualitative conclusions from the endocrine data, the data related to mass of organic content had a larger amount of variance attributed to relevant biological contrasts and a lower amount of variance attributed to individual variation, compared with data related to total dry mass of extracted material. Compared with data expressed as dry mass of extracted material, data expressed as mass of organic content may provide a more refined and statistically powerful measure of endocrine activity in species that ingest large amounts of indigestible material.     

Effects of elevated atmospheric [CO2] on instantaneous transpiration efficiency at leaf and canopy scales in Eucalyptus saligna

Rising atmospheric concentrations of CO₂ (C_a) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to C_a. We hypothesized that plants regulate stomatal conductance optimally in response to rising C_a. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate‐controlled whole‐tree chambers for 2 years at ambient and elevated C_a. Elevated C_a was ambient + 240 ppm, 60% higher than ambient C_a. Leaf‐scale gas exchange was measured throughout the second year of the study and leaf‐scale ITE increased by 60% under elevated C_a, as predicted. Values of leaf‐scale ITE depended strongly on vapour pressure deficit (D) in both CO₂ treatments. Whole‐canopy CO₂ and H₂O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between C_a treatments, which had important effects on values of canopy‐scale ITE. However, when C_a treatments were compared at the same D, canopy‐scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy‐scale ITE were not significantly different, indicating that ITE was not scale‐dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to C_a. The effect of elevated C_a on photosynthesis increased with rising D. At high D, C_a had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of C_a on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with C_a will allow us to predict the effects of C_a on transpiration rate.     

Common variants in the CD36 gene are associated with oral fat perception, fat preferences, and obesity in African Americans

Animal studies show that CD36, a fatty acid translocase, is involved in fat detection and preference, but these findings have not been reported in humans. The objective of this study was to determine whether human genetic variation in 5 common CD36 polymorphisms is associated with oral fat perception of Italian salad dressings, self-reported acceptance of high-fat foods and obesity in African-American adults (n = 317). Ratings of perceived oiliness, fat content, and creaminess were assessed on a 170-mm visual analogue scale (VAS) in response to salad dressings that were 5%, 35%, and 55% fat-by-weight content. Acceptance of added fats and oils and high-fat foods was self-reported and anthropometric measures were taken in the laboratory. DNA was isolated from saliva and genotyped at 5 CD36 polymorphisms. Three polymorphisms, rs1761667, rs3840546, and rs1527483 were associated with the outcomes. Participants with the A/A genotype at rs1761667 reported greater perceived creaminess, regardless of the fat concentration of the salad dressings (P < 0.01) and higher mean acceptance of added fats and oils (P = 0.02) compared to those with other genotypes at this site. Individuals who had C/T or T/T genotypes at rs1527483 also perceived greater fat content in the salad dressings, independent of fat concentration (P = 0.03). BMI and waist circumference were higher in participants who were homozygous for a deletion (D/D) at rs3840546, compared to I/D or D/D individuals (P < 0.001), but only 2 D/D individuals were tested, so this finding needs replication. This is the first study to demonstrate an association between common variants in CD36 and fat ingestive behaviors in humans.     

Discovery of novel phosphonate derivatives as hepatitis C virus NS3 protease inhibitors

A novel class of phosphonate derivatives was designed to mimic the interaction of product-like carboxylate based inhibitors of HCV NS3 protease. A phosphonic acid (compound 2) was demonstrated to be a potent HCV NS3 protease inhibitor, and a potential candidate for treating HCV infection. The syntheses and preliminary biological evaluation of this phosphonate class of inhibitor are described.