The absence of crossovers on chromosome 4 in Drosophila melanogaster: Imperfection or interesting exception?

Drosophila melanogaster chromosome 4 is an anomaly because of its small size, chromatin structure, and most notably its lack of crossing over during meiosis. Earlier ideas about the absence of crossovers on 4 hypothesize that these unique characteristics function to prevent crossovers. Here, we explore hypotheses about the absence of crossovers on 4, how these have been addressed, and new insights into the mechanism behind this suppression. We review recently published results that indicate that global crossover patterning, in particular the centromere effect, make a major contribution to the prevention of crossovers on 4.     

The effects of temperature on host-pathogen interactions in D. melanogaster: who benefits?

Drosophila melanogaster is widely used to study immune system function in insects. However, little work has been done in D. melanogaster on the effect of temperature on the immune system. Here we describe experiments that demonstrate that cooler temperatures enhance survival after infection and alter expression of immune-related genes in flies. This effect appears to be due not only to the fact that colder temperatures slow down bacterial growth, but also to the beneficial effects of cooler temperature on immune function. We explore the possibility that heat shock proteins, and in particular, Hsp83, may improve immune function at cool temperatures. We have long known that temperature can alter immune responses against microbial pathogens in insects. The approach described here allows us to determine whether this effect is due primarily to temperature-specific effects on the host or on its pathogen. These results suggest that both may be important.     

The circadian basis of ovarian diapause regulation in Drosophila melanogaster: is the period gene causally involved in photoperiodic time measurement?

Females of a wild-type strain of Drosophila melanogaster (Canton-S), and of several clock mutants (period), were able to discriminate between diapause-inducing short days and diapause-averting long days with a well-defined critical daylength. The critical daylengths of a short-period mutant (pers) and a long-period mutant (perL2) were almost identical, both to each other and to that of Canton-S. The critical daylength of an arrhythmic mutant (perol), however, was about 3 hr shorter than that of Canton-S, and that of per- was about 5 hr shorter. Exposure of Canton-S females to Nanda-Hamner experiments, consisting of a 10-hr photophase coupled to a dark phase varying between 4 and 74 hr, showed (1) that the photoperiodic clock in D. melanogaster measures nightlength rather than daylength, and (2) that photoperiodic time measurement is somehow based on (or affected by) constituent oscillators in the circadian system. Nanda-Hamner results for the period mutants all showed similar profiles regardless of genotype, or the presence or absence of per locus DNA. These results suggest that photoperiodic induction and locomotor activity do not share a common pacemaker in D. melanogaster, and that the per gene is not causally involved in nightlength measurement by the photoperiodic clock, although flies in which the per locus is missing (per-) or defective (perol) show an altered critical value.     

The I--R system of hybrid dysgenesis in Drosophila melanogaster: are I factor insertions responsible for the mutator effect of the I--R interaction?

Summary When Drosophila melanogaster males coming from a class of strains known as inducer are crossed with females from the complementary class (reactive), a quite specific kind of sterile female (SF) is obtained that exhibits other dysgenic traits such as non-disjunctions and non-randomly distributed mutations. This syndrome is caused by the interaction of the I factor linked to inducer chromosomes with the maternally inherited reactive state R. This I-R interaction is also responsible for chromosomal contamination that is likely to result from very frequent I factor insertions into reactive chromosomes. Such insertions might be responsible for the I-R induced mutations and some data concerning this hypothesis are reported here.Out of nine I-R-generated mutants one, the white ^IR1 (w ^IR1) allele, is closely linked to an I factor, which maps either at the site of the mutation or within less than 0.02 map units. In addition, w ^IR1 is somewhat unstable when transmitted through SF females.In contrast, the typical I factor does not seem to be associated with any of the eight other mutants as judged by their inability to induce the female sterility characteristic of the I-R syndrome. The possibility is discussed that most of I-R-induced mutations are nevertheless caused by insertions of either undetectable I factors or other transposable elements, not related to I, whose transposition is dependent on the I-R interaction.     

Does the difference in the timing of eclosion of the fruit fly Drosophila melanogaster reflect differences in the circadian organization?

The eclosion rhythm of a laboratory population of Drosophila melanogaster was studied under 12h light, 12h dark (LD 12:12) cycles. Although most of the flies were found to eclose just after “lights on” in LD 12:12, termed within gate (WG) flies, a few flies were found to eclose nearly 10h after peak eclosion, termed outside gate (OG) flies. The circadian parameters of the clocks controlling oviposition rhythms in the WG and the OG flies were estimated to understand the cause of such differences in the timing of eclosion. The distribution of the fraction of individual flies exhibiting single, multiple, and no significant period in the WG flies was significantly different from distribution in the OG flies. Compared to the WG flies, more OG flies were found to exhibit oviposition rhythm with multiple periodicity, whereas more WG flies exhibited an oviposition rhythm with a single significant period. The fraction of flies with arrhythmic oviposition was similar in both the WG and the OG flies. Free-running period τ in constant darkness (DD) and the phase angle difference ψ in LD 12:12 for the oviposition rhythm of WG and OG flies were significantly different. These results suggest that the differences in the time of eclosion between the flies eclosing within the gate and outside the gate of eclosion are probably due to differences in the circadian system controlling eclosion, which is reflected by the differences in their oviposition rhythm. (Chronobiology International, 18(4), 601-612, 2001)     

The maternal effect mutation sésame affects the formation of the male pronucleus in Drosophila melanogaster

After entering the oocyte and before the formation of the diploid zygote, the sperm nucleus is transformed into a male pronucleus, a process that involves a series of conserved steps in sexually reproducing animals. Notably, a major modification of the male gamete lies in the decondensation of the highly compact sperm chromatin. We present here the phenotype of sésame (ssm), a maternal effect mutation which affects the formation of the male pronucleus in Drosophila melanogaster. Homozygous ssm(185b) females produce haploid embryos which develop with only the maternally derived chromosomes. These haploid embryos die at the end of embryogenesis. Cytological analyses of the fertilization in eggs laid by ssm(185b) mutant females showed that both pronuclear migration and pronuclear apposition occurred normally. However, a dramatic alteration of the male pronucleus by which its chromatin failed to fully decondense was systematically observed. Consequently, the affected male pronucleus does not enter the first mitotic spindle, which is organized around only the maternally derived chromosomes. Immunodetection of lamina antigens indicates that a male pronuclear envelope is able to form around the partially decondensed paternal chromatin. This suggests that the maternally provided sésame(+) function is required for a late stage of sperm chromatin remodeling.     

Chromosome Localization of the λ20p1.4 clone of the Drosophila melanogaster Nuclear Lamina DNA in the melanogaster Species Subgroup of the Genus Drosophila (Sophophora)

Chromosome localization of sequences homologous to 20p1.4 of the Drosophila melanogaster nuclear lamina DNA (nlDNA) was established by in situ hybridization in species of the melanogastersubgroup. DNA of the 20p1.4 clone was shown to be located in the chromocenter in all the species examined. Laboratory strains of D. simulans, D. mauritiana, andD. sechellia exhibited interspecific differences in localization of 20p1.4 nlDNA on chromosome arms. In eight natural populations, intraspecific polymorphism of 20p1.4 nlDNA chromosome localization was shown to be present in D. simulans but absent in D. melanogaster. The possible participation of transposable elements in 20p1.4 nlDNA relocation is discussed.     

The distribution of the P–M hybrid dysgenesis system in Drosophila melanogaster strains from Brazil

Wild-caught flies of Drosophila melanogaster from seven natural populations of extreme regions of Brazil (São Luís, MA; Teresina, PI; Rio Cipó, MG; Maringá, PR; São José do Rio Preto, SP; Joinville, SC; and Porto Alegre, RS) were studied with the purpose of evaluating hybrid dysgenesis due to mobilization of P elements and the regulatory capacity of the strains' cytotypes. Diagnostic crosses were made and the strains classified according to their P–M phenotypes. Four strains were classified as moderate P (MA, MG, PI, and SP), two as Q (PR and RS) and one as M′ (SC). Females of southern strains (PR, SC, and RS) presented in A crosses lower degrees of gonadal dysgenesis scores than those from northern strains (MA and PI).     

Selection at the α-Gpdh locus in experimental populations of Drosophila melanogaster

Three sets of experiments have been conducted in order to evaluate the role of natural selection at the -Gpdh locus in Drosophila melanogaster. (1) The evolution of the F-allele frequency has been followed for many generations in 13 experimental populations having different genetic backgrounds. (2) Egg-to-adult viability has been measured in synthetic populations derived from one locality (Brouilly) and the results have been compared with those of a previous experiment involving a different local population (Tostes). (3) The effects of sodium octanoate on egg-to-adult viability have been measured on the genotypes FF, FS, SF, and SS. The results demonstrate that selection operates on a small block of genes which includes the -Gpdh locus.ERA 406 CNRS: Analyse et mécanismes de maintien du polymorphisme.     

The localization of “ordinary” sex-linked genes in section 20 of the polytene X chromosome of Drosophila melanogaster

A cytogenetic procedure is described whereby a combination of polytene chromosome analysis and complementation mapping has permitted the unequivocal localization of ordinary sex-linked genes (those not covered by the Y-chromosome) in Section 20, the most proximal region of Bridges' (1938) map of the polytene X-chromosome. Thus far, eleven functional units in Section 20 distal to the bobbed locus, but none proximal, have been resolved. We suggest that the polytenized portion of Section 20, which heretofore has traditionally been considered as heterochromatic, corresponds, in fact, with the euchromatic portion of the mitotic X-chromosome.     

A test for enhancement of cytotype regulation in Drosophila melanogaster by the transposase-encoding P Element ∆2-3

Transposable P elements are regulated in the germ line by piRNAs, which are small RNAs that associate with the Piwi class of proteins. This regulation, called the P cytotype, is enhanced by genetic interactions between P elements that are primary sources of these RNAs and other P elements. The enhanced regulation is thought to reflect amplification of the primary piRNAs by cleavage of mRNAs derived from the other P elements through a mechanism called the ping-pong cycle. We tested the transposase-encoding P element known as ?2-3 for its ability to enhance cytotype regulation anchored in P elements inserted at the telomere of the left arm of the X chromosome (TP elements). The ?2-3 P element lacks the intron between exons 2 and 3 in the structurally complete P element (CP). Unlike the CP element, it does not markedly enhance cytotype regulation anchored in TP elements, nor does it transmit transposase activity through the egg cytoplasm. However, mRNAs from both the CP and ?2-3 elements are maternally deposited in embryos. These observations suggest that maternally transmitted CP mRNA enhances cytotype regulation by participating in the ping-pong cycle and that it encodes the P transposase in the embryonic germ line, whereas maternally transmitted ?2-3 mRNA does not, possibly because it is not efficiently directed into the primordial embryonic germ line. Strong transposon regulation may, therefore, require ping-pong cycling with maternally inherited mRNAs in the embryo.     

The Mechanisms Underlying α-Amanitin Resistance in Drosophila melanogaster: A Microarray Analysis

The rapid evolution of toxin resistance in animals has important consequences for the ecology of species and our economy. Pesticide resistance in insects has been a subject of intensive study; however, very little is known about how Drosophila species became resistant to natural toxins with ecological relevance, such as α-amanitin that is produced in deadly poisonous mushrooms. Here we performed a microarray study to elucidate the genes, chromosomal loci, molecular functions, biological processes, and cellular components that contribute to the α-amanitin resistance phenotype in Drosophila melanogaster. We suggest that toxin entry blockage through the cuticle, phase I and II detoxification, sequestration in lipid particles, and proteolytic cleavage of α-amanitin contribute in concert to this quantitative trait. We speculate that the resistance to mushroom toxins in D. melanogaster and perhaps in mycophagous Drosophila species has evolved as cross-resistance to pesticides, other xenobiotic substances, or environmental stress factors.     

Cytotype Regulation of P Transposable Elements in Drosophila melanogaster: Repressor Polypeptides or piRNAs?

The telomeric P elements TP5 and TP6 are associated with the P cytotype, a maternally inherited condition that represses P-element-induced hybrid dysgenesis in the Drosophila germ line. To see if cytotype repression by TP5 and TP6 might be mediated by the polypeptides they could encode, hobo transgenes carrying these elements were tested for expression of mRNA in the female germ line and for repression of hybrid dysgenesis. The TP5 and TP6 transgenes expressed more germ-line mRNA than the native telomeric P elements, but they were decidedly inferior to the native elements in their ability to repress hybrid dysgenesis. These paradoxical results are inconsistent with the repressor polypeptide model of cytotype. An alternative model based on the destruction of P transposase mRNA by Piwi-interacting (pi) RNAs was supported by finding reduced P mRNA levels in flies that carried the native telomeric P elements, which are inserted in a known major piRNA locus.     

How does Drosophila melanogaster overwinter?

In temperate regions low temperatures seem to be the most restrictive factor for survival of Drosophila natural populations, which depends on the capacity of one or more developmental stages to resist unfavourable winter conditions. In this study we have attempted to answer the question of how D. melanogaster overwinters under natural temperature conditions. Only adults overwintered and no diapause was observed in any developmental stage. Thus, developmental duration becomes a decisive component with respect to overwintering potential and, therefore, the preadult stages are unlikely to overwinter. Possible evolutionary steps in adaptation to cold regions are discussed.     

Enzyme specificity: “pseudopolymorphism” of lactate dehydrogenase in Drosophila melanogaster

An electrophoretic variant in the LDH (l-lactate:NAD oxidoreductase, E.C.1.1.1.27) of Drosophila melanogaster was observed on starch (or polyacrylamide) gels. This variant was found to exhibit an identical isozymic pattern (three isozymes with a decreasing staining density) on starch gel and map position as the Adh locus. On the other hand, anodal polyacrylamide gel electrophoresis in crude extracts has shown LDH to consist of nine bands and ADH of four bands. We have shown that ADH (Alcohol:NAD oxidoreductase, E.C.1.1.1.1) also oxidizes l(+)-lactate or d(–)-lactate with the NAD, while LDH oxidizes ethanol. By using various genetic and biochemical techniques, we have shown that the observed Ldh electrophoretic variant was not a real one and could be attributed to the presence of ADH. We have called this phenomenon pseudopolymorphism, and the problem of enzyme specificity has been examined. The appearance of a band in an assay using lactic acid as a substrate is not sufficient evidence for the presence of LDH. Hence, caution is called for before characterizing an electrophoretic band on a gel as being equivalent to the presence of a genetic locus. Out of the nine electrophoretic zones of activity observed on polyacrylamide gel (or out of the six previously observed) using crude extract, only two (one major and one minor) belong to LDH, as revealed by purified enzyme preparations. Furthermore, purified LDH exhibits activity in two bands on starch gel (out of three observed in crude extracts), which appear in different positions as compared with those of ADH. Finally, one band which responds to the presence of d(–)-lactate but not to l(+)-lactate has been revealed.     

The chaperone domain BRICHOS prevents CNS toxicity of amyloid-β peptide in Drosophila melanogaster

Aggregation of the amyloid-β peptide (Aβ) into toxic oligomers and amyloid fibrils is linked to the development of Alzheimer’s disease (AD). Mutations of the BRICHOS chaperone domain are associated with amyloid disease and recent in vitro data show that BRICHOS efficiently delays Aβ42 oligomerization and fibril formation. We have generated transgenic Drosophila melanogaster flies that express the Aβ42 peptide and the BRICHOS domain in the central nervous system (CNS). Co-expression of Aβ42 and BRICHOS resulted in delayed Aβ42 aggregation and dramatic improvements of both lifespan and locomotor function compared with flies expressing Aβ42 alone. Moreover, BRICHOS increased the ratio of soluble:insoluble Aβ42 and bound to deposits of Aβ42 in the fly brain. Our results show that the BRICHOS domain efficiently reduces the neurotoxic effects of Aβ42, although significant Aβ42 aggregation is taking place. We propose that BRICHOS-based approaches should be explored with an aim towards the future prevention and treatment of AD.KEY WORDS: Amyloid, Alzheimer’s disease, Protein misfolding, Chaperone     

Positive and Negative Selection in the β-Esterase Gene Cluster of the Drosophila melanogaster Subgroup

We examine the pattern of molecular evolution of the β-esterase gene cluster, including the Est-6 and ψEst-6 genes, in eight species of the Drosophila melanogaster subgroup. Using maximum likelihood estimates of nonsynonymous/synonymous rate ratios, we show that the majority of Est-6 sites evolves under strong (48% of sites) or moderate (50% of sites) negative selection and a minority of sites (1.5%) is under significant positive selection. Est-6 sites likely to be under positive selection are associated with increased intraspecific variability. One positively selected site is responsible for the EST-6 F/S allozyme polymorphism; the same site is responsible for the EST-6 functional divergence between species of the melanogaster subgroup. For ψEst-6 83.7% sites evolve under negative selection, 16% sites evolve neutrally, and 0.3% sites are under positive selection. The positively selected sites of ψEst-6 are located at the beginning and at the end of the gene, where there is reduced divergence between D. melanogaster and D. simulans; these regions of ψEst-6 could be involved in regulation or some other function. Branch-site-specific analysis shows that the evolution of the melanogaster subgroup underwent episodic positive selection. Collating the present data with previous results for the β-esterase genes, we propose that positive and negative selection are involved in a complex relationship that may be typical of the divergence of duplicate genes as one or both duplicates evolve a new function. [Reviewing Editor: Dr. Martin Kreitman]     

The existence of LSP-1βS in Drosophila melanogaster natural populations in two northern states

LSP-1^S is present in Michigan and Massachusetts Drosophila melanogaster natural populations. Its frequency, 10%, is significantly higher in an East Jordan, Mich. (latitude, 45.10° N), population than in East Lansing, Mich. (latitude 42.44° N), or Hadley, Mass. (latitude, 42.21° N), populations, where it averages 3% at each location. The average frequency of LSP-2^S is more comparable, 6, 5, and 7% at East Jordan, East Lansing, and Hadley, respectively. LSP-1^F variants are also present. A total of 342 single third-instar larvae was scored for LSP-1 autosomal variants, and 323 for LSP-2 variants. Each larva represented a newly established isofemale line from collections at East Jordan in 1981 and 1983, East Lansing in 1982, and Hadley in 1981, 1982, and 1983. Within localities, frequencies of hemolymph protein variants did not differ significantly between years. Proteins 9, 10, 11, and 15 correspond to the LSP-1, , and triplet and LSP-2 polypeptide in D. melanogaster. Our results together with those of Singh and Coulthart [(1982). Genetics 102:437] indicate that D. melanogaster populations in north temperate climates maintain considerable genetic heterogeneity for the larval hemolymph proteins.     

Variations of male cuticular hydrocarbons with geoclimatic variables: an adaptative mechanism in Drosophila melanogaster?

7-tricosene (7T) and 7-pentacosene (7P) are the major components of cuticular hydrocarbons in Drosophila simulans and D. melanogaster males. A chemical study of 16 isofemale lines of D. melanogaster sampled at the first and eighth generations in laboratory conditions showed the stability of chromatographical profiles. Then a large scale study of male 7T/7P polymorphism was performed with 85 populations of D. melanogaster and 29 of D. simulans collected all over the world. There were significant correlations of the values of the balanced ratio (7T − 7P)/(7T + 7P) with geo-climatic parameters, such as latitude, longitude, mean temperature, temperature range and vapour pressure. Parallel variations were also reported for the homologous linear alkanes (23 and 25 Carbon atoms) but not for the longer branched alkanes (27 and 29 Carbon atoms). No correlation was significant for the D. simulans populations studied. In this species a similar polymorphism of 7T/7P was found but restricted to a few populations from West Equatorial Africa. This revised version was published online in July 2006 with corrections to the Cover Date.