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PubMed1996

Identification and genetic analysis of wunen, a gene guiding Drosophila melanogaster germ cell migration.

We describe a novel genetic locus, wunen (wun), required for guidance of germ cell migration in early Drosophila development. Loss of wun function does not abolish movement but disrupts the orientation of the motion causing the germ cells to disperse even though their normal target, the somatic gonad, is well formed. We demonstrate that the product of this gene enables a signal to pass from the soma to the germ line and propose that the function of this signal is to selectively stabilize certain cytoplasmic extensions resulting in oriented movement. To characterize this guidance factor, we have mapped wun to within 100 kb of cloned DNA.

Alleles↗
PubMed1996

Physical map of the malaria vector Anopheles gambiae.

Random cDNA clones, cosmid clones and RAPD polymorphic fragments have been localized by in situ hybridization to the ovarian nurse cell polytene chromosomes of the malaria vector Anopheles gambiae. We thus established 85 molecular markers for 110 sites within the whole A. gambiae polytene chromosome complement. The cDNA clones analyzed were isolated at random, and their exact localizations were determined by in situ hybridization. For 15 of the cDNA clones, a partial nucleotide sequence has been obtained; for nine of them sequence searches in the GenBank database revealed high degrees of similarity with published sequences. The cosmid clones analyzed were obtained as the result of screening with a few of the aforementioned cDNA clones of particular interest, or taken from a small set of randomly isolated cosmid clones. The RAPD clones are polymorphic fragments, potentially diagnostic for the various chromosomal forms of A. gambiae that are currently being analyzed.

Animals↗
PubMed1996

Genetics of a difference in male cuticular hydrocarbons between two sibling species, Drosophila simulans and D. sechellia.

In seven of the eight species of the Drosophila melanogaster group, the predominant cuticular hydrocarbon of males is 7-tricosene, but in the island endemic species D. sechellia it is 6-tricosene. The phylogeny of the group implies that the novel hydrocarbon profile of D. sechellia is a derived character. Genetic analysis of hybrids between D. sechellia and its close relative D. simulans show that each of the five major chromosome arms carries at least one gene affecting the ratio of the two tricosene isomers, with the right arm of the third chromosome having the largest effect. The species difference in this character is therefore polygenic with the effects of the different chromosome arms generally additive, although there is some epistasis among third-chromosome genes. Observations of courtship by males who have been coated with foreign hydrocarbons suggest that a male's hydrocarbon profile may slightly affect the degree of sexual isolation in one of the reciprocal hybridizations between these species, but that this role is small compared to that played by hydrocarbon differences between females.

Alkenes↗
PubMed1996

The Drosophila Eip78C gene is not vital but has a role in regulating chromosome puffs.

We have generated a number of chromosomal aberrations that disrupt the early-late ecdysone-induced 78C puff gene (Eip78C, ecdysone-induced protein, FlyBase name for the E78 gene of Stone and Thummel 1993), which encodes the two members of the nuclear hormone receptor superfamily Eip78C-A and Eip78C-B. The aberrations include deletions of the ligand-binding/dimerization domain of both, inversions that split Eip78C-A but retain residual Eip78C-B expression, and a small deletion specific for Eip78C-B. We find that wild-type Eip78C functions are completely dispensable for normal development under laboratory conditions. However, we show that Eip78C-B is required for the maximal puffing activity of a subset of late puffs (63E and 82F) since these puffs are reduced in size in Eip78C-B mutant backgrounds. Paradoxically the same late puffs are reduced, as well as at least one other, when the Eip78C-B cDNA is overexpressed from a heat shock promoter. These data indicate either that Eip78C function is redundant or that it plays a subtle modulating role in the regulation of chromosome puffing.

Amino Acid Sequence↗
PubMed1996

Polygenic mutation in Drosophila melanogaster: genetic interactions between selection lines and candidate quantitative trait loci.

We have investigated genetic interactions between spontaneous mutations affecting abdominal and sternopleural bristle number that have accumulated in 12 long-term selection lines derived from an inbred strain, and mutations at 14 candidate bristle number quantitative trait loci. The quantitative test for complementation was to cross the selection lines to an inbred wild-type strain (the control cross) and to a derivative of the control strain into which the mutant allele at the candidate locus to be tested was substituted (the tester strain). Genetic interactions between spontaneous mutations affecting bristle number and the candidate locus mutations were common, and in several cases the interaction effects were different in males and females. Analyses of variance of the (tester- control) differences among and within groups of replicate lines selected in the same direction for the same trait showed significant group effects for several candidate loci. Genetically, the interactions could be caused by allelism of, and/ or epistasis between, spontaneous mutations in the selection lines and the candidate locus mutations. It is possible that much of the response to selection was from new mutations at candidate bristle number quantitative trait loci, and that for some of these loci, mutation rates were high.

Analysis of Variance↗
PubMed1997

Trans-suppression of terminal deficiency-associated position effect variegation in a Drosophila minichromosome.

Position effect variegation (PEV) is the clonal inactivation of euchromatic or heterochromatic genes that are abnormally positioned within a chromosome. PEV can be influenced by modifiers in trans, including single gene mutations and the total amount of heterochromatin present in the genome. Terminal deletions of a Drosophila minichromosome (Dp1187) dramatically increase PEV of a yellow+ body-color gene located in cis, even when the terminal break is > 100 kb distal to the yellow gene. Here we demonstrate that terminal deficiency-associated PEV can be suppressed by the presence of a second minichromosome, a novel phenomenon termed "trans-suppression." The chromosomal elements responsible for trans-suppression were investigated using a series of minichromosomes with molecularly characterized deletions and inversions. The data suggest that trans-suppression does not involve communication between transcriptional regulatory elements on the homologues, a type of transvection known to act at the yellow locus. Furthermore, trans-suppression is not accomplished by titration through the addition of extra centric heterochromatin, a general mechanism for PEV suppression. We demonstrate that trans-suppression is disrupted by significant changes in the structure of the suppressing minichromosome, including deletions of the yellow region and centric heterochromatin, and large inversions of the centric heterochromatin. We conclude that chromosome pairing plays an important role in trans-suppression and discuss the possibility that terminal deficiency-associated PEV and trans-suppression reflect changes in nuclear positioning of the chromosomes and the gene, and/or the activity and distribution of telomere-binding proteins.

Animals↗
PubMed1998

Enhancer of Polycomb is a suppressor of position-effect variegation in Drosophila melanogaster.

Polycomb group (PcG) genes of Drosophila are negative regulators of homeotic gene expression required for maintenance of determination. Sequence similarity between Polycomb and Su(var)205 led to the suggestion that PcG genes and modifiers of position-effect variegation (PEV) might function analogously in the establishment of chromatin structure. If PcG proteins participate directly in the same process that leads to PEV, PcG mutations should suppress PEV. We show that mutations in E(Pc), an unusual member of the PcG, suppress PEV of four variegating rearrangements: In(l)wm4, B(SV), T(2;3)Sb(V) and In(2R)bw(VDe2). Using reversion of a Pelement insertion, deficiency mapping, and recombination mapping as criteria, homeotic effects and suppression of PEV associated with E(Pc) co-map. Asx is an enhancer of PEV, whereas nine other PcG loci do not affect PEV. These results support the conclusion that there are fewer similarities between PcG genes and modifiers of PEV than previously supposed. However, E(Pc) appears to be an important link between the two groups. We discuss why Asx might act as an enhancer of PEV.

Animals↗
PubMed1999

The relationship between allozyme and chromosomal polymorphism inferred from nucleotide variation at the Acph-1 gene region of Drosophila subobscura.

The Acph-1 gene region was sequenced in 51 lines of Drosophila subobscura. Lines differ in their chromosomal arrangement for segment I of the O chromosome (O(st) and O(3+4)) and in the Acph-1 electrophoretic allele (Acph-1(100), Acph-1(054), and Acph-1(>100)). The ACPH-1 protein exhibits much more variation than previously detected by electrophoresis. The amino acid replacements responsible for the Acph-1(054) and Acph-1(>100) electrophoretic variants are different within O(st) and within O(3+4), which invalidates all previous studies on linkage disequilibrium between chromosomal and allozyme polymorphisms at this locus. The Acph-1(>100) allele within O(3+4) has a recent origin, while both Acph-1(054) alleles are rather old. Levels of nucleotide variation are higher within the O(3+4) than within the O(st) arrangement except for nonsynonymous sites. The McDonald and Kreitman test shows a significant excess of nonsynonymous polymorphisms within O(st) when D. guanche is used as the outgroup. According to the nearly neutral model of molecular evolution, this excess is consistent with a smaller effective size of O(st) relative to O(3+4) arrangements. A smaller population size, a lower recombination, and a more recent bottleneck might be contributing to the smaller effective size of O(st).

Acid Phosphatase↗
PubMed2003

Natural selection drives Drosophila immune system evolution.

Evidence from disparate sources suggests that natural selection may often play a role in the evolution of host immune system proteins. However, there have been few attempts to make general population genetic inferences on the basis of analysis of several immune-system-related genes from a single species. Here we present DNA polymorphism and divergence data from 34 genes thought to function in the innate immune system of Drosophila simulans and compare these data to those from 28 nonimmunity genes sequenced from the same lines. Several statistics, including average K(A)/K(S) ratio, average silent heterozygosity, and average haplotype diversity, significantly differ between the immunity and nonimmunity genes, suggesting an important role for directional selection in immune system protein evolution. In contrast to data from mammalian immunoglobulins and other proteins, we find no strong evidence for the selective maintenance of protein diversity in Drosophila immune system proteins. This may be a consequence of Drosophila's generalized innate immune response.

Animals↗
PubMed2004

Excess of amino acid substitutions relative to polymorphism between X-linked duplications in Drosophila melanogaster.

We have obtained sequence polymorphism data from 13 genes belonging to 5 gene families in Drosophila melanogaster where the K(a)/K(s) between copies is greater than 1. Twelve of these 13 loci are X-linked. In general, there is evidence of purifying selection in all families, as inferred both from levels of silent and replacement variation and insertion/deletion variation, suggesting that the loci are likely functional. Shared polymorphisms indicative of gene conversion between paralogs are rare among the X-linked families, in contrast to available data from autosomal duplicates. McDonald-Kreitman tests between duplicates reveal an excess of amino-acid fixations between copies in the X-linked families, suggesting that the divergence between these loci was driven by positive selection. In contrast, available data from autosomal duplicates show a deficit of fixations, consistent with gene conversion being a strong homogenizing force.

Amino Acid Substitution↗
PubMed1999

Sex-specific organisation of middle repetitive DNA sequences in the mealybug Planococcus lilacinus.

Differential organisation of homologous chromosomes is related to both sex determination and genomic imprinting in coccid insects, the mealybugs. We report here the identification of two middle repetitive sequences that are differentially organised between the two sexes and also within the same diploid nucleus. These two sequences form a part of the male-specific nuclease-resistant chromatin (NRC) fraction of a mealybug Planococcus lilacinus. To understand the phenomenon of differential organisation we have analysed the components of NRC by cloning the DNA sequences present, deciphering their primary sequence, nucleosomal organisation, genomic distri-bution and cytological localisation. Our observations suggest that the middle repetitive sequences within NRC are functionally significant and we discuss their probable involvement in male-specific chromatin organisation.

Animals↗
PubMed1997

UbcD1, a Drosophila ubiquitin-conjugating enzyme required for proper telomere behavior.

The end-to-end association of chromosomes through their telomeres has been observed in normal cells of certain organisms, as well as in senescent and tumor cells. The molecular mechanisms underlying this phenomenon are currently unknown. We show here that five independent mutant alleles in the Drosophila UbcD1 gene cause frequent telomere-telomere attachments during both mitosis and male meiosis that are not seen in wild type. These telomeric associations involve all the telomeres of the D. melanogaster chromosome complement, albeit with different frequencies. The pattern of telomeric associations observed in UbcD1 mutants suggests strongly that the interphase chromosomes of wild-type larval brain cells maintain a Rab1 orientation within the nucleus, with the telomeres and centromeres segregated to opposite sides of the nucleus. The UbcD1 gene encodes a class I ubiquitin-conjugating (E2) enzyme. This indicates that ubiquitin-mediated proteolysis is normally needed to ensure proper telomere behavior during Drosophila cell division. We therefore suggest that at least one of the targets of UbcD1 ubiquitination is a telomere-associated polypeptide that may help maintain proper chromosomal orientation during interphase.

Animals↗
PubMed2002

Genetics of a difference in pigmentation between Drosophila yakuba and Drosophila santomea.

Drosophila yakuba is a species widespread in Africa, whereas D. santomea, its newly discovered sister species, is endemic to the volcanic island of São Tomé in the Gulf of Guinea. Drosophila santomea probably formed after colonization of the island by its common ancestor with D. yakuba. The two species differ strikingly in pigmentation: D. santomea, unlike the other eight species in the D. melanogaster subgroup, almost completely lacks dark abdominal pigmentation. D. yakuba shows the sexually dimorphic pigmentation typical of the group: both sexes have melanic patterns on the abdomen, but males are much darker than females. A genetic analysis of this species difference using morphological markers shows that the X chromosome accounts for nearly 90% of the species difference in the area of abdomen that is pigmented and that at least three genes (one on each major chromosome) are involved in each sex. The order of chromosome effects on pigmentation area are the same in males and females, suggesting that loss of pigmentation in D. santomea may have involved the same genes in both sexes. Further genetic analysis of the interspecific difference between males in pigmentation area and intensity using molecular markers shows that at least five genes are responsible, with no single locus having an overwhelming effect on the trait. The species difference is thus oligogenic or polygenic. Different chromosomal regions from each of the two species influenced pigmentation in the same direction, suggesting that the species difference (at least in males) is due to natural or sexual selection and not genetic drift. Measurements of sexual isolation between the species in both light and dark conditions show no difference, suggesting that the pigmentation difference is not an important cue for interspecific mate discrimination. Using DNA sequence differences in nine noncoding regions, we estimate that D. santomea and D. yakuba diverged about 400,000 years ago, a time similar to the divergences between two other well-studied pair of species in the subgroup, both of which also involved island colonization.

Animals↗
PubMed1996

The polyubiquitin gene of the mosquito Anopheles gambiae: structure and expression.

The polyubiquitin gene from the mosquito Anopheles gambiae has been cloned and sequenced, and its structure is reported along with sequence analysis results. The gene consists of approximately seven tandem head-to-tail repeat units of the seventy-six amino acid-coding ubiquitin monomer. It is expressed constitutively in larvae, pupae and adults of An. gambiae, as well as in a cell line derived from this mosquito species. A probe made from a DNA fragment containing the coding region of the gene recognizes transcripts of approximately 3.6 kb and 4.4 kb in RNA isolated from all mosquito developmental stages and a unique transcript of approximately 3.0 kb in RNA from the cell line. Single monomeric units of the An. gambiae polyubiquitin gene shared from 75.9% to 85.5% identity at the DNA level with homologous sequences from other organisms ranging from yeast to man. A comparison of individual repeat units of the An. gambiae gene revealed that, in general, the 5' ends of the individual monomers are more highly conserved than the 3' ends. The gene mapped by in situ hybridization on ovarian nurse cell polytene chromosomes to a primary site at division 12C on chromosome 2R and to a secondary site at division 9C on the same chromosome.

Amino Acid Sequence↗
PubMed1987

Experimental hybridization between members of the Simulium damnosum complex.

Males of the Beffa form of Simulium soubrense Vajime and Dunbar were successfully crossed with female S.squamosum V. & D. and S.sanctipauli V. & D. Fertile eggs from both crosses were reared to larvae and, in the case of the Beffa x squamosum cross, to adults. Larval chromosomes from the Beffa x sanctipauli cross had normally paired homologues but those of the Beffa x squamosum cross showed extensive asynapsis and large heterozygous loops. The morphology of the larval and adult hybrids from the Beffa x squamosum cross were more characteristic of squamosum, but the adult males had scutal patterns typical of the Beffa form and retained this form's laboratory-mating propensity.

Animals↗
PubMed1994

Tandemly arranged repeats of a novel highly charged 16-amino-acid motif representing the major component of the sperm-tail-specific axoneme-associated protein family Dhmst101 form extended alpha-helical rods within the extremely elongated spermatozoa of Drosophila hydei.

We have previously reported that the sperm-tail-specific proteins in Drosophila hydei, encoded by the small Dhmst101 gene family, contained several tandem repeats of a novel highly charged, well-conserved cysteine-containing motif of 16 amino acids, KKKCAEAAKKEKEAAE [Neesen, J., Bünemann, H. & Heinlein, U. A. O. (1994) Dev. Biol. 162, 414-425] and suggested that this motif might be important in the structural and functional integrity of the sperm tail. We tested this suggestion by examining structure formation by model synthetic peptides containing the 16-residue sequence and corresponding peptides with one and two repeats of the sequence with Cys being replaced by Ala. We find that all these peptides form monomeric alpha-helices and that the helix content is considerably enhanced as the number of tandem repeats increases. These results are consistent with tandemly arranged 16-amino-acid repeats in Dhmst101 proteins forming extended alpha-helical rods, with the highly conserved Cys present in each 16-amino-acid motif being involved in regular interhelical cross-linking, thus providing a rigid, stable framework within the extremely elongated spermatozoa of Drosophila hydei.

Amino Acid Sequence↗
PubMed2000

Colonization of America by Drosophila subobscura: spatial and temporal lethal-gene allelism.

About twenty years ago Drosophila subobscura, a western Palearctic species, colonized both North and South America. Lethal genes in the O chromosome has been subject to much research. Lethal gene allelisms between American populations far away have been studied. These allelisms were not negligible, but all cases were due to the lethal gene completely associated to the O5 chromosomal inversion. Here we analyze the lethal genes in a new American population of D. subobscura (Centralia, Washington), located fairly close to a previously studied population (Bellingham, Washington) and separated in space and time with other American populations (Gilroy I and II in California and Santiago de Chile). The frequencies of lethal and semilethal genes of Centralia were 16.9+/-4.6 and 6.2+/-3.0, respectively. The intrapopulational allelism of Centralia was 0.122+/-0.036. Interpopulational allelisms were studied using the lethal genes from the populations separated in space and time from Centralia. The interpopulational allelisms between Centralia and Gilroy I (California) and between Centralia and Bellingham (Washington) were higher than the intrapopulational allelism (0.155+/-0.032 and 0.153+/-0.024, respectively). In all these cases allelism was due to a complete association between a lethal gene and the O5 chromosomal inversion. Accordingly, no other lethal genes are shared in these populations.

Alleles↗