Environmentally constrained mutation and adaptive evolution in Salmonella

The relationship between environment and mutation is complex [1]. Claims of Lamarkian mutation [2] have proved unfounded [3], [4] and [5]; it is apparent, however, that the external environment can influence the generation of heritable variation, through either direct effects on DNA sequence [6] or DNA maintenance and copying mechanisms [7], [8], [9] and [10], or as a consequence of evolutionary processes [11], [12], [13], [14], [15] and [16]. The spectrum of mutational events subject to environmental influence is unknown [6] and precisely how environmental signals modulate mutation is unclear. Evidence from bacteria suggests that a transient recombination-dependent hypermutational state can be induced by starvation [5]. It is also apparent that chnages in the mutability of specific loci can be influenced by alterations in DNA topology [10] and [17]. Here we describe a remarkable instance of adaptive evolution in Salmonella which is caused by a mutation that occurs in intermediate-strength osmotic environments. We show that the mutation is not ‘directed’ and describe its genetic basis. We also present compelling evidence in support of the hypothesis that the mutational event is constrained by signals transmitted from the external environment via changes in the activity of DNA gyrase.     

Ontogeny of hemoglobins: Evidence for hemoglobin M

A new autosomal codominant hemoglobin mutation alters hemoglobin M of the primitive red cell line and hemoglobin D found in definitive cells. That Hb M and Hb D are altered by the same gene mutation supports the idea that Hb M shares a polypeptide chain with Hb D. It is concluded that in the switch from primitive hemoglobins to those of the definitive type, there are at least two α chains conserved; α^A of Hb E in Hb A and α^D of Hb M in Hb D.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Prevalence of neural tube defects in South Australia, 1966-91: effectiveness and impact of prenatal diagnosis.

OBJECTIVE--To determine trends in total prevalence of neural tube defects in South Australia during 1966-91, the impact of prenatal diagnosis on birth prevalence, and the effectiveness of prenatal screening for neural tube defects in 1986-91. DESIGN--All births and terminations of pregnancy affected by neural tube defects and information on prenatal screening were ascertained from multiple sources including the South Australian perinatal and abortion statistics collections, birth defects register, and state maternal serum alpha fetoprotein screening programme. SETTING--Southern Australia. SUBJECTS--All 1058 births and terminations of pregnancy affected by neural tube defects in 1966-91. MAIN OUTCOME MEASURES--Total prevalence and birth prevalence of individual and all neural tube defects. The proportion of screened cases detected prenatally. RESULTS--Total prevalence of neural tube defects during 1966-91 was 2.01/1000 births with no upward or downward trend. However, birth prevalence fell significantly (by 5.1% a year), with an 84% reduction from 2.29/1000 births in 1966 to 0.35/1000 in 1991 (relative risk = 0.16, 95% confidence interval 0.07 to 0.34). The fall was 96% for anencephaly and 82% for spina bifida. 85% of defects, both open and closed, were detected before 28 weeks'' gestation in women screened by serum alpha fetoprotein or mid-trimester ultrasonography, or both, in 1986-91 (99.0% for anencephaly and 75.7% for spina bifida). CONCLUSIONS--While the total prevalence of neural tube defects in South Australia remained stable, prenatal diagnosis and termination of pregnancy resulted in an 84% fall in birth prevalence during 1966-91. Screening detected over four fifths of cases in 1986-91.     

Intraspecific diversity in the fungal speciesChaunopycnis alba: Implications for microbial screening programs

Intraspecific variation among 84 isolates of the anamorphic fungusChaunopycnis alba from 26 different geographical locations was analyzed by investigating optimal growth temperatures, differences in the production of secondary metabolites and presence or absence of the cyclosporin synthetase gene. The genetic diversity was assessed using random amplified polymorphic DNA (RAPD). Analysis of these data showed high genetic, metabolic and physiological diversity within this species. Isolates from the Antarctic represented the most homogeneous group withinC. alba and together with isolates from the Arctic these polar strains differed from alpine, temperate and tropical strains by low optimal growth temperatures and by low production of secondary metabolites. Isolates from tropical climes were characterized by high optimal growth temperatures and by the production of comparatively diverse metabolite spectra. Most of the isolates that were similar in the combination of their physiological and metabolic characters were also genetically related. Isolates from different geographical origins did not show many similarities, with the exception of the cyclosporin A-producing isolates, and large diversity could be observed even within a single habitat. This leads us to the suggestion that for pharmaceutical screening programs samples should be collected from a diversity of different geographical and climatic locations. For the selection of strains for screening the RAPD assay seems to be the most powerful tool. It reflected the highest intraspecific diversity and the results corresponded well with the other characteristics.     

No evidence of inbreeding avoidance or inbreeding depression in a social carnivore

Dispersal by young mammals away from their natal site is generallythought to reduce inbreeding, with its attendant negative fitnessconsequences. Genetic data from the dwarf mongoose, a pack-livingcarnivore common in African savannas, indicate that there areexceptions to this generalization. In dwarf mongoose populationsin the Serengeti National Park, Tanzania, breeding pairs arecommonly related, and close inbreeding has no measurable effecton offspring production or adult survival. Inbreeding occursbecause average relatedness among potential mates within a packis high, because mating patterns within the pack are randomwith respect to the relatedness of mates, and because dispersaldoes little to decrease the relatedness among mates. Young femalesare more likely to leave a pack when the dominant male is aclose relative but are relatively infrequent dispersers. Youngmales emigrate at random with respect to the relatedness ofthe dominant female and tend to disperse to packs that containgenetically similar individuals.[Behav Ecol 7: 480–489(1996)]     

Erythropoiesis in normal and mutant chick embryos

Hemoglobin D_Davis (Hb D_D), an autosomal codominant in chickens, the α^D-globin chain of Hb M of primitive cells and Hb D of definitive erythrocytes. Erythropoiesis and Hb synthesis was investigated in normal, heterozygous, and homozygous Hb D_D mutant embryos (stages 15–44) and adults. The time of appearance, morphology, relationships to developmental changes, and number of primitive and definitive cells were determined. Primitive hemoglobins between stages 17 and 44 showed four components, P1, P2, E, and M (or M_D), on high-resolution isoelectric focusing gels. Comparison of $\text{P1}\text{P2}$ ratios in the four phenotypes indicated that homozygous Hb D_D embryos had an increased proportion of Hb P2 relative to Hb P1 between stages 17 and 35. This difference coincided with an increase in the number of large primitive cells. In all phenotypes the proportions of primitive hemoglobins decreased after stage 25 and they were not detected after stage 40. Basophilic definitive erythroblasts were present in cell suspensions from all phenotypes between stages 24 and 25. Hb A, the major Hb and Hb D, the minor Hb, of definitive cells of embryos and adults were detected by isoelectric focusing of lysates by stage 29. Definitive cells from late embryos of all phenotypes had higher proportions of Hb D (or Hb D_D) than did red cells from corresponding adult birds. Heterozygous Hb D_D embroys and adults had both Hb D and Hb D_D. Hb D_D comprises about 30% of the total minor Hb rather than 50% expected for heterozygosity at a single locus. In this respect heterozygous Hb D_D chick embryos and adult birds are similar to certain heterozygous α-chain variants in humans. A minor Hb, H, found in lysates of later embryos disappears in lysates of normal chicks 65 days after hatching, but was present in the circulation of homozygous Hb D_D chicks until at least 195 days after hatching. Additionally, several minor Hb components which may be asymmetrical hybrids or derived precursors of Hb A and Hb D (or Hb D_D) were observed. This study provides the precise developmental stages when the switchover of erythroid cell populations and hemoglobins in the chick embryo occurs. This is the first investigation of an α-globin chain mutant which is synthesized during all stages of red cell development and may be a useful animal model for the study of hemoglobinopathies in vertebrates.     

Role of lipid peroxidation in the inhibition of mononuclear cell proliferation by normal lipoproteins

Stimulated peripheral blood mononuclear cells (PBMC) can oxidize normal lipoproteins, and sufficiently oxidized lipoproteins are cytotoxic. However, the role of lipid peroxidation in the inhibition of mitogen-stimulated PBMC proliferation by physiologic concentrations of normal lipoproteins is unclear. In the present investigation, normal low density lipoprotein (LDL) and very low density lipoprotein (VLDL) suppressed [3H]thymidine incorporation and gamma interferon production in concanavalin A-stimulated PBMC without causing cell death. This suppression was accompanied by parallel increases in lipid peroxidation products measured as thiobarbituric acid reactive substances (TBARS). In contrast, high density lipoprotein (HDL) failed to inhibit PBMC and TBARS remains low. Differences between the PBMC suppression from LDL, VLDL, and HDL were best accounted for by normalizing the lipoprotein concentrations by their total lipid content. Moreover, the antioxidants superoxide dismutase and butylated hydroxytoluene each substantially ameliorated the inhibition of PBMC caused by LDL, and reduced the levels of lipid peroxidation products that were generated. Altogether, these results suggest that reactive oxygen species generated by stimulated PMBC may cause oxidative alterations of normal lipoproteins that may, in turn, account for much of the previously reported inhibition of PBMC by normal lipoproteins.     

Eradicating Helicobacter pylori and symptoms of non-ulcer dyspepsia.

OBJECTIVE--To examine the effect of eradication of Helicobacter pylori on symptoms of non-ulcer dyspepsia. DESIGN--Four week prospective study. SETTING--One hospital outpatient and endoscopy department. PATIENTS--90 adults with persistent symptoms typical of non-ulcer dyspepsia but no clinical or endoscopic evidence of other peptic, biliary, pancreatic, or malignant disease; all had histological and microbiological evidence of infection with H pylori. 83 patients completed the treatment regimen. INTERVENTION--Colloidal bismuth subcitrate 120 mg four times a day for four weeks (27 patients); metronidazole 400 mg and amoxycillin 500 mg each three times a day for one week (27); and bismuth subcitrate 120 mg four times a day for four weeks, metronidazole 400 mg three times a day for one week, plus amoxycillin 500 mg three times a day for the first week (29). MAIN OUTCOME MEASURES--Change in symptom scores determined with questionnaire; histological evidence of gastritis and microbiological evidence of presence of H pylori in biopsy specimens. RESULTS--Overall, H pylori was eradicated in 41 (49%) patients. Although gastritis scores improved significantly in only patients in whom H pylori had been eradicated (from 1.56 to 0.61, p less than 0.01 v from 1.83 to 1.07, p = 0.52) mean symptom scores after treatment were similar in patients in whom H pylori had or had not been eradicated (3.0 v 2.3, NS). Similarly the mean symptom score improved whether or not gastritis improved (2.8 v 3.1 respectively, p = 0.72). The observations were similar for treatment groups analysed individually. CONCLUSION--Antral infection with the organism does not seem to have an important aetiological role in non-ulcer dyspepsia short term.