Allele-specific population structure of Drosophila melanogaster alcohol dehydrogenase at the molecular level

The history of the Drosophila melanogaster alcohol dehydrogenase (ADH) Fast/Slow polymorphism was studied by recording molecular variation and inversion polymorphism in 233 chromosomes from European and African populations. Silent molecular variation in the Slow allele was very different between standard chromosomes and chromosomes bearing the In(2L)t inversion. Within populations, inverted Slow haplotypes were more variable than standard Slow haplotypes. Between populations, geographical structure was almost nonexistent for inverted Slow haplotypes and highly significant for standard Slow. All Fast haplotypes occurred on standard chromosomes. They showed little variation within and between populations. They were highly significantly closer to standard Slow haplotypes from Europe. These results suggest that the current range of Fast and In(2L)t Slow haplotypes is recent and that an older genetic differentiation between populations was followed by allele-specific gene flow.     

Contrasting patterns of nucleotide sequence variation at the glucose dehydrogenase (Gld) locus in different populations of Drosophila melanogaster

We have analyzed nucleotide sequence variation at the Glucose dehydrogenase (Gld) locus from four populations of Drosophila melanogaster from four continents. All four population samples show a significant reduction in silent variation compared to the neutral expectation. The levels of silent variation across all four populations are consistent with the predictions of the background selection model; however, Zimbabwe has a remarkably low level of variation. In the face of dramatically reduced silent polymorphism, an amino acid variant, leading to the common allozyme polymorphism at Gld, remains in low to intermediate frequency in all non-African samples. In the Chinese population sample, the ratio of replacement to silent variation is significantly elevated compared to the neutral expectation. The difference in patterns of variation across these population samples suggests that selection on Gld (or the Gld region) has been different in the Chinese population than in the other three.     

Relation between the space flight-induced frequency of dominant lethal mutations and the level of allozyme heterozygosity in Drosophila melanogaster populations

Currently, the treatment of falciparum malaria is seriously compromised by spreading drug resistance. We studied the effects of camptothecin, a potent and specific topoisomerase I inhibitor, on erythrocytic malaria parasites in vitro. In Plasmodium falciparum, camptothecin trapped protein-DNA complexes, inhibited nucleic acid biosynthesis, and was cytotoxic. These results provide proof for the concept that topoisomerase I is a vulnerable target for new antimalarial drug development.     

Glycosidases are present on the surface of Drosophila melanogaster spermatozoa

We investigated the presence of enzymes on the surface of Drosophila melanogaster spermatozoa that might bind the carbohydrate residues of the egg shell. Spectrophotometric and fluorimetric studies were used on whole spermatozoa to assay galactosyltransferase and glycosidase activities. No galactosyltransferase is present on the sperm surface, whereas two glycosidases, beta-N-acetylglucosaminidase (GlcNAc'ase) and alpha-mannosidase (Man'ase), have been evidenced. They have an optimal pH of 6-6.5 and 4, respectively. The same glycosidases were detected as soluble forms probably secreted by the seminal vesicle epithelium. We suggest that these enzymes might be involved in the recognition of alpha-mannose and beta-N-acetylglucosamine residues present on the egg shell at the site of sperm entry.     

Naturally occurring variation in bristle number and DNA polymorphisms at the scabrous locus of Drosophila melanogaster

The association between quantitative genetic variation in bristle number and molecular variation at a candidate neurogenic locus, scabrous, was examined in Drosophila melanogaster. Approximately 32 percent of the genetic variation in abdominal bristle number (21 percent for sternopleural bristle number) among 47 second chromosomes from a natural population was correlated with DNA sequence polymorphisms at this locus. Several polymorphic sites associated with large phenotypic effects occurred at intermediate frequency. Quantitative genetic variation in natural populations caused by alleles that have large effects at a few loci and that segregate at intermediate frequencies conflicts with the classical infinitesimal model of the genetic basis of quantitative variation.     

Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex

Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1-kbp portion of the yolk protein 2 locus, were sequenced in six individuals from each of four species: Drosophila melanogaster, D. simulans, D. mauritiana, and D. sechellia. The species and strains were the same as those of a previous study of a 1.9-kbp region of the period locus. No evidence was found for recent balancing or directional selection or for the accumulation of selected differences between species. Yolk protein 2 has a high level of amino acid replacement variation and a low level of synonymous variation, while zeste has the opposite pattern. This contrast is consistent with information on gene function and patterns of codon bias. Polymorphism levels are consistent with a ranking of effective population sizes, from low to high, in the following order: D. sechellia, D. melanogaster, D.mauritiana, and D. simulans. The apparent species relationships are very similar to those suggested by the period locus study. In particular, D. simulans appears to be a large population that is still segregating variation that arose before the separation of D. mauritiana and D. sechellia. It is estimated that the separation of ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The separations of D. sechellia and D. mauritiana from ancestral D. simulans appear to have occurred 0.58-0.86 Mya, with D. mauritiana having diverged from ancestral D. simulans 0.1 Myr more recently than D. sechellia.     

Genetic controls of meiotic recombination and somatic DNA metabolism in Drosophila melanogaster

Recombination-defective meiotic mutants and mutagen-sensitive mutants of D. melanogaster have been examined for their effects on meiotic chromosome behavior, sensitivity to killing by mutagens, somatic chromosome integrity, and DNA repair processes. Several loci have been identified that specify functions that are necessary for both meiotic recombination and DNA repair processes, whereas mutants at combination and DNA repair processes, whereas mutants at other loci appear to be defective in only one pathway of DNA processing.     

Mutation "outbursts" of various genes in natural populations of Drosophila melanogaster

The evaluation and treatment of older men with benign prostatic hyperplasia (BPH) is complicated by the highly variable clinical presentation of men with BPH, which ranges from minor urinary symptoms to acute urinary retention. Treatment choices have expanded with recent advances in medical and surgical therapies. Surgical treatment includes open prostatectomy and transurethral prostatectomy as well as newer technologies that are less invasive and that result in fewer long-term side effects. Response to treatment depends on the patient and should be directed at symptom relief.     

Altered gene expression and genetic damage in North American fish populations

Populations of marine, estuarine, and freshwater fish from highly urban and industrialized sites in North America often exhibit elevated prevalences of neoplastic, preneoplastic, and nonneoplastic hepatic lesions, and sometimes epidermal neoplasms compared to conspecifics from more pristine reference locales. Positive statistical associations with environmental concentrations of PAHs and other xenobiotics and experimental laboratory studies suggest a chemical etiology to these epizootics. Studies have investigated the expression of carcinogenically relevant genes, the extent of overall DNA damage, somatic cell mutations, germ line polymorphisms, and overall levels of genetic diversity in fish from these populations and other polluted sites. In general, elevated levels of cytochrome P4501A expression have been found in fish from contaminated locales; however, inhibition of gene induction has been seen in hepatic lesions and in normal tissue in fish from the most contaminated sites, perhaps due to genetic adaptation or physiological acclimation. Levels of bulky hepatic DNA adducts, as detected by 32P-postlabeling, are almost always elevated in fish from populations that are exposed to highly contaminated environments. However, levels of DNA adducts were not always predictive of the vulnerability to neoplasia of populations and species from polluted sites. Elevated levels of oxygen radical-induced DNA damage have been observed in hepatic tumors, preneoplastic lesions, and normal livers in a single species of flatfish from contaminated sites; however, the prevalences of these alterations in other species and at other polluted sites has yet to be evaluated. Frequent alterations in the K-ras oncogene have been reported in hepatic neoplasms in several species from highly contaminated sites and also in embryos that were experimentally exposed to oil-contaminated sediments. Studies also suggest that heritable germ line polymorphisms, altered allelic frequencies, and reductions in overall genetic diversity may have occurred in some highly impacted populations; however, the origin and functional significance of altered allelic frequencies have largely yet to be evaluated. In summary, feral fish appear particularly sensitive to DNA alterations from xenobiotics, perhaps due to their unusually high levels of exposure, relatively inefficient DNA repair, and the high frequency of polyploidy in some taxa and provide excellent models to explore the relationships between xenobiotic exposure and altered gene structure and expression.     

Mitochondrial DNA haplotype frequencies in natural and experimental populations of Drosophila subobscura

The evolution of Drosophila subobscura mitochondrial DNA has been studied in experimental populations, founded with flies from a natural population from Esporles (Majorca, Balearic Islands, Spain). This population, like other European ones, is characterized by the presence of two very common (>96%) mitochondrial haplotypes (called I and II) and rare and endemic haplotypes that appear at very low frequencies. There is no statistical evidence of positive Darwinian selection acting on the mitochondrial DNA variants according to Tajima's neutrality test. Two experimental populations, with one replicate each, were established with flies having a heterogeneous nuclear genetic background, which was representative of the composition of the natural population. Both populations were started with the two most frequent mitochondrial haplotypes, but at different initial frequencies. After 13 to 16 generations, haplotype II reached fixation in three cages and its frequency was 0.89 by generation 25 in the fourth cage. Random drift can be rejected as the force responsible for the observed changes in haplotype frequencies. There is not only statistical evidence of a linear trend favoring a mtDNA (haploid) fitness effect, but also of a significant nonlinear deviation that could be due to a nuclear component.     

Probable mechanisms underlying interallelic complementation and temperature-sensitivity of mutations at the shibire locus of Drosophila melanogaster

The shibire locus of Drosophila melanogaster encodes dynamin, a GTPase required for the fission of endocytic vesicles from plasma membrane. Biochemical studies indicate that mammalian dynamin is part of a complex containing multiple dynamin subunits and other polypeptides. To gain insight into sequences of dynamin critical for its function, we have characterized in detail a collection of conditional and lethal shi alleles. We describe a probable null allele of shi and show that its properties are distinct from those of two classes of lethal alleles (termed I and II) that show intergroup, interallelic complementation. Sequenced class I alleles, which display dominant properties, carry missense mutations in conserved residues in the GTPase domain of dynamin. In contrast, the sequenced class II alleles, which appear completely recessive, carry missense mutations in conserved residues of a previously uncharacterized "middle domain" that lies adjacent to the GTPase region. These data suggest that critical interactions mediated by this middle domain are severely affected by the class II lethal mutations; thus, the mutant sequences should be very useful for confirming the in vivo relevance of interactions observed in vitro. Viable heteroallelic combinations of shi lethals show rapid and reversible temperature-sensitive paralytic phenotypes hitherto only described for the ts alleles of shi. When taken together with the molecular analysis of shi mutations, these observations suggest that the GTPase domain of dynamin carries an intrinsically temperature-sensitive activity: hypomorphic mutations that reduce this activity at low temperatures result in conditional temperature-sensitive phenotype. These observations explain why screens for conditional paralytic mutants in Drosophila inevitably recover ts alleles of shi at high frequencies.