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PubMed1988

Characterization of new Punch mutations: identification of two additional mutant classes.

The Punch locus of Drosophila melanogaster which encodes the pteridine biosynthetic enzyme, GTP cyclohydrolase, is genetically complex. Lethal alleles of the locus resolve into an array of interallelic complementation groups, and at least one class of mutations is developmentally specific, affecting GTP cyclohydrolase activity only in the heads of adults. All previously isolated Punch alleles were identified on the basis of a mutant eye color phenotype. By screening mutagenized chromosomes over Punch region deficiencies, we have now isolated new alleles on the basis of lethal and visible phenotypes. Most of these alleles fall into previously identified genetic classes, but two new classes of mutations were also found. One class contains two alleles that behave as dominant lethal mutations in some genetic backgrounds. The other class represents a second developmentally specific set of alleles that affect the function of the Punch locus only during embryogenesis.

Alleles↗

PubMed1989

Interaction of the Enhancer of white-apricot with transposable element alleles at the white locus in Drosophila melanogaster.

The Enhancer of wa [E(wa)] mutation was shown to interact strongly with 4 of 41 tested alleles of the white (w) eye color locus. All four of the affected w alleles result from the insertion of a transposable element. E(wa) was further localized cytogenetically. The locus lies between the breakpoints of T(Y;2)L11 and T(Y;2)H137 (section 60) in 2R. The original mutation was shown to be antimorphic on the basis of its action in the presence of additional normal copies and the ability to revert the original allele to one that mimics the effect of a deficiency for the locus. The RNA transcribed from wa was analyzed from flies segregating for E(wa) and normal. The low level of normal functional messenger RNA present in white-apricot is reduced further in Enhancer homozygotes. Total copia RNA was also examined on Northern analyses from the segregating population but no quantitative change in the major copia RNA was produced by E(wa) homozygotes compared to normal.

Alleles↗

PubMed1990

Genetic analysis of the enhancer of zeste locus and its role in gene regulation in Drosophila melanogaster.

The Enhancer of zeste [E(z)] locus of Drosophila melanogaster is implicated in multiple examples of gene regulation during development. First identified as dominant gain-of-function modifiers of the zeste1-white (z-w) interaction, mutant E(z) alleles also produce homeotic transformations. Reduction of E(z)+ activity leads to both suppression of the z-w interaction and ectopic expression of segment identity genes of the Antennapedia and bithorax gene complexes. This latter effect defines E(z) as a member of the Polycomb-group of genes. Analysis of E(z)S2, a temperature-sensitive E(z) allele, reveals that both maternally and zygotically produced E(z)+ activity is required to correctly regulate the segment identity genes during embryonic and imaginal development. As has been shown for other Polycomb-group genes, E(z)+ is required not to initiate the pattern of these genes, but rather to maintain their repressed state. We propose that the E(z) loss-of-function eye color and homeotic phenotypes may both be due to gene derepression, and that the E(z)+ product may be a general repressing factor required for both examples of negative gene regulation.

Alleles↗

PubMed1991

Molecular and functional analysis of the mariner mutator element Mos1 in Drosophila.

The white-peach allele in Drosophila results from insertion of the transposable element mariner. The particular copy that is inserted in white-peach is an inactive copy referred to as the peach element. The peach element is excised at a high rate in the presence of active copies of mariner located elsewhere in the genome, and the excision of peach in somatic cells is recognized phenotypically by the occurrence of eye-color mosaicism in white-peach flies. Active mariner elements identified by their ability to induce high levels of white-peach mosaicism are denoted Mos (Mosaic) factors. We have sequenced and functionally analyzed the factor Mos1 originally identified in Drosophila mauritiana. The Mos1 element is 1286 base pairs in length, the same length as the peach element. It differs from the peach element in 11 nucleotide positions distributed throughout its length, including four amino acid replacements in the long open reading frame. Analysis of chimeric constructs between Mos1 and peach implies that functionally important differences occur in both the 5' and 3' halves of Mos1. A mariner element identical in sequence to Mos1 yields lower levels of mosaicism in transformants, implying that adjacent flanking sequences have important effects on Mos1 activity. Another mariner element, designated Ma351, isolated from a nonmosaic strain of D. mauritiana, differs from Mos1 in just three nucleotide positions. When introduced into the germline, Ma351 yields various levels of white-peach mosaicism depending on insertion site. These results imply that the activity of mariner elements is determined jointly by their own nucleotide sequences, by the effects of adjacent flanking sequences, and by longer-range position effects.

Amino Acid Sequence↗

PubMed1991

A trans-acting regulatory gene that inversely affects the expression of the white, brown and scarlet loci in Drosophila.

A trans-acting regulatory gene, Inr-a, that alters the level of expression of the white eye color locus as an inverse function of the number of its functional copies is described. Several independent lines of evidence demonstrate that this regulatory gene interacts with white via the promoter sequences. Among these are the observations that the inverse regulatory effect is conferred to the Adh gene when fused to the white promoter and that cis-regulatory mutants of white fail to respond. The phenotypic response to Inr-a is found in all tissues in which white is expressed, and mutants of the regulator exhibit a recessive lethality during larval periods. Increased white messenger RNA levels in pupal stages are found in Inr-a/+ individuals versus +/+ and a coordinate response is observed for mRNA levels from the brown and scarlet loci. All are structurally related and participate in pigment deposition. These experiments demonstrate that a single regulatory gene can exert an inverse effect on a target structural locus, a situation postulated from segmental aneuploid studies of gene expression and dosage compensation.

Alcohol Dehydrogenase↗

PubMed1993

Genetic and cytogenetic analysis of the 43A-E region containing the segment polarity gene costa and the cellular polarity genes prickle and spiny-legs in Drosophila melanogaster.

A cytogenetic analysis of the 43A-E region of chromosome 2 in Drosophila melanogaster is presented. Within this interval 27 complementation groups have been identified by extensive F2 screens and ordered by deletion mapping. The region includes the cellular polarity genes prickle and spiny-legs, the segmentation genes costa and torso, the morphogenetic locus sine oculis and is bounded on its distal side by the eye-color gene cinnabar. In addition 19 novel lethal complementation groups and two semi-lethal complementation groups with morphogenetic escaper phenotypes are described.

Alleles↗

PubMed1995

White as a reporter gene to detect transcriptional silencers specifying position-specific gene expression during Drosophila melanogaster eye development.

The white+ gene was used as a reporter to detect transcriptional silencer activity in the Drosophila genome. Changes in the spatial expression pattern of white were scored in the adult eye as nonuniform patterns of pigmentation. Thirty-six independent P[lacW] transposant lines were collected. These represent 12 distinct pigmentation patterns and probably 21 loci. The spatial pigmentation pattern is due to cis-acting suppression of white+ expression, and the suppression probably depends on cell position rather than cell type. The mechanism of suppression differs from inactivation by heterochromatin. In addition, activation of lacZ in P[lacW] occurs also in specific patterns in imaginal discs and embryos in many of the lines. The expression patterns of white+ and lacZ may reflect the activity of regulatory elements belonging to an endogenous gene near each P[lacW] insertion site. We speculate that these putative POSE (position-specific expression) genes may have a role in pattern formation of the eye as well as other imaginal structures. Three of the loci identified are optomotor-blind, engrailed and invected. teashirt is also implicated as a candidate gene. We propose that this "silencer trap"' may be an efficient way of identifying genes involved in imaginal pattern formation.

ATP-Binding Cassette Transporters↗

PubMed1996

Rearrangements involving repeated sequences within a P element preferentially occur between units close to the transposon extremities.

In a previous report we described rearrangements occurring at a high rate (30% of the progeny of dysgenic flies) within a cluster of 5S genes internal to a P element. These events were characterized as precise amplifications and deletions of 5S units. Here we analyze recombination events within P elements containing two repeated arrays of 5S genes flanking a central white gene. Deletions (50%) and duplications (3%) of the white gene together with various amounts of flanking 5S genes were observed. These recombinations occur preferentially between the most external 5S units of P transposons. Such rearrangements could be favored by interactions between the proteins bound to the P terminal sequences.

ATP-Binding Cassette Transporters↗

PubMed1996

Somatic reversion of chromosomal position effects in Drosophila melanogaster.

A transgene was inserted at several different chromosomal sites in Drosophila melanogaster, where its expression was subject to genomic position effects. Quantitative position effects and variegated and constant patterned position effects were observed. We investigated the status of the affected gene in the somatic cells where it normally functions. The FLP site-specific recombinase was used to remove the gene from the chromosome and its expression was then evaluated. We show that the FLP recombinase functions in cells that have finished their developmental program of mitoses. When FLP acts on directly repeated copies of its target site (FRT), the DNA flanked by those FRTs is excised from the chromosome as a closed circle. The extrachromosomal circle is maintained in nondividing cells, and a gene located on such a circle can be expressed. We then demonstrate that a gene subject to either variegated or constant position effect can be relieved of that effect by excision of the gene from the chromosome in cells where it would otherwise be inactive. We also observed a strong inhibition of FLP-mediated recombination for target sites located near centric heterochromatin.

ATP-Binding Cassette Transporters↗

PubMed1997

Mobilization of a Minos transposon in Drosophila melanogaster chromosomes and chromatid repair by heteroduplex formation.

Transposase-mediated mobilization of the element Minos has been studied in the Drosophila melanogaster genome. Excision and transposition of a nonautonomous Minos transposon in the presence of a Minos transposase gene was detected with a dominant eye color marker carried by the transposon. Frequencies of excision in somatic tissues and in the germ line were higher in flies heterozygous for the transposon than in homozygotes or hemizygotes. Transposition of a X chromosome-linked insertion of Minos into new autosomal sites occurred in 1-12% of males expressing transposase, suggesting that this system is usable for gene tagging and enhancer trapping in Drosophila. Sequence analysis of PCR-amplified donor sites after excision showed precise restoration of the original target sequence in approximately 75% of events in heterozygotes and the presence of footprints or partially deleted elements in the remaining events. Most footprints consisted of the four terminal bases of the transposon, flanked by the TA target duplication. Sequencing of a chromosomal donor site that was directly cloned after excision showed a characteristic two-base mismatch heteroduplex in the center of the 6-bp footprint. Circular extrachromosomal forms of the transposon, presumably representing excised Minos elements, could be detected only in the presence of transposase. A model for chromatid repair after Minos excision is discussed in which staggered cuts are first produced at the ends of the inverted repeats, the broken chromatid ends are joined, and the resulting heteroduplex is subsequently repaired. The model also suggests a simple mechanism for the production of the target site duplication and for regeneration of the transposon ends during reintegration.

Animals↗

PubMed1998

white+ transgene insertions presenting a dorsal/ventral pattern define a single cluster of homeobox genes that is silenced by the polycomb-group proteins in Drosophila melanogaster.

We used the white gene as an enhancer trap and reporter of chromatin structure. We collected white+ transgene insertions presenting a peculiar pigmentation pattern in the eye: white expression is restricted to the dorsal half of the eye, with a clear-cut dorsal/ventral (D/V) border. This D/V pattern is stable and heritable, indicating that phenotypic expression of the white reporter reflects positional information in the developing eye. Localization of these transgenes led us to identify a unique genomic region encompassing 140 kb in 69D1-3 subject to this D/V effect. This region contains at least three closely related homeobox-containing genes that are constituents of the iroquois complex (IRO-C). IRO-C genes are coordinately regulated and implicated in similar developmental processes. Expression of these genes in the eye is regulated by the products of the Polycomb-group (Pc-G) and trithorax-group (trx-G) genes but is not modified by classical modifiers of position-effect variegation. Our results, together with the report of a Pc-G binding site in 69D, suggest that we have identified a novel cluster of target genes for the Pc-G and trx-G products. We thus propose that ventral silencing of the whole IRO-C in the eye occurs at the level of chromatin structure in a manner similar to that of the homeotic gene complexes, perhaps by local compaction of the region into a heterochromatin-like structure involving the Pc-G products.

ATP-Binding Cassette Transporters↗

PubMed1998

Mutation in P0, a dual function ribosomal protein/apurinic/apyrimidinic endonuclease, modifies gene expression and position effect variegation in Drosophila.

In a search for modifiers of gene expression with the white eye color gene as a target, a third chromosomal P-element insertion mutant l(3)01544 has been identified that exhibits a strong pigment increase in a white-apricot background. Molecular analysis shows that the P-element insertion is found in the first intron of the gene surrounding the insertion site. Sequencing both the cDNA and genomic fragments revealed that the identified gene is identical to one encoding ribosomal protein P0/apurinic/apyrimidinic endonuclease. The P-element-induced mutation, l(3)01544, affects the steady-state level of white transcripts and transcripts of some other genes. In addition, l(3)01544 suppresses the variegated phenotypes of In(1)wm4h and In(1)y3P, suggesting a potential involvement of the P0 protein in modifying position effect variegation. The revertant generated by the precise excision of the P element has lost all mutant phenotypes. Recent work revealed that Drosophila ribosomal protein P0 contains an apurinic/apyrimidinic endonuclease activity. Our results suggest that this multifunctional protein is also involved in regulation of gene expression in Drosophila.

Alleles↗

PubMed2000

The oxen gene of Drosophila encodes a homolog of subunit 9 of yeast ubiquinol-cytochrome c oxidoreductase complex: evidence for modulation of gene expression in response to mitochondrial activity.

A P-element insertion in the oxen gene, ox(1), has been isolated in a search for modifiers of white gene expression. The mutation preferentially exerts a negative dosage effect upon the expression of three genes encoding ABC transporters involved in pigment precursor transport, white, brown, and scarlet. A precise excision of the P element reverts the mutant phenotype. Five different transcription units were identified around the insertion site. To distinguish a transcript responsible for the mutant phenotype, a set of deletions within the oxen region was generated. Analysis of gene expression within the oxen region in the case of deletions as well as generation of transgenic flies allowed us to identify the transcript responsible for oxen function. It encodes a 6.6-kD homolog of mitochondrial ubiquinol cytochrome c oxidoreductase (QCR9), subunit 9 of the bc(1) complex in yeast. In addition to white, brown, and scarlet, oxen regulates the expression of three of seven tested genes. Thus, our data provide additional evidence for a cellular response to changes in mitochondrial function. The oxen mutation provides a model for the genetic analysis in multicellular organisms of the effect of mitochondrial activity on nuclear gene expression.

ATP-Binding Cassette Transporters↗

PubMed2001

Whole-genome effects of ethyl methanesulfonate-induced mutation on nine quantitative traits in outbred Drosophila melanogaster.

We induced mutations in Drosophila melanogaster males by treating them with 21.2 mm ethyl methanesulfonate (EMS). Nine quantitative traits (developmental time, viability, fecundity, longevity, metabolic rate, motility, body weight, and abdominal and sternopleural bristle numbers) were measured in outbred heterozygous F3 (viability) or F2 (all other traits) offspring from the treated males. The mean values of the first four traits, which are all directly related to the life history, were substantially affected by EMS mutagenesis: the developmental time increased while viability, fecundity, and longevity declined. In contrast, the mean values of the other five traits were not significantly affected. Rates of recessive X-linked lethals and of recessive mutations at several loci affecting eye color imply that our EMS treatment was equivalent to approximately 100 generations of spontaneous mutation. If so, our data imply that one generation of spontaneous mutation increases the developmental time by 0.09% at 20 degrees and by 0.04% at 25 degrees, and reduces viability under harsh conditions, fecundity, and longevity by 1.35, 0.21, and 0.08%, respectively. Comparison of flies with none, one, and two grandfathers (or greatgrandfathers, in the case of viability) treated with EMS did not reveal any significant epistasis among the induced mutations.

Alleles↗

PubMed2002

Unexpected stability of mariner transgenes in Drosophila.

A number of mariner transformation vectors based on the mauritiana subfamily of transposable elements were introduced into the genome of Drosophila melanogaster and examined for their ability to be mobilized by the mariner transposase. Simple insertion vectors were constructed from single mariner elements into which exogenous DNA ranging in size from 1.3 to 4.5 kb had been inserted; composite vectors were constructed with partial or complete duplications of mariner flanking the exogenous DNA. All of the simple insertion vectors showed levels of somatic and germline excision that were at least 100-fold lower than the baseline level of uninterrupted mariner elements. Although composite vectors with inverted duplications were unable to be mobilized at detectable frequencies, vectors with large direct duplications of mariner could be mobilized. A vector consisting of two virtually complete elements flanking exogenous DNA yielded a frequency of somatic eye-color mosaicism of approximately 10% and a frequency of germline excision of 0.04%. These values are far smaller than those observed for uninterrupted elements. The results imply that efficient mobilization of mariner in vivo requires the presence and proper spacing of sequences internal to the element as well as the inverted repeats.

Animals↗

PubMed2003

The Drosophila roX1 RNA gene can overcome silent chromatin by recruiting the male-specific lethal dosage compensation complex.

The Drosophila MSL complex consists of at least six proteins and two noncoding roX RNAs that mediate dosage compensation. It acts to remodel the male's X chromatin by covalently modifying the amino terminal tails of histones. The roX1 and roX2 genes are thought to be nucleation sites for assembly and spreading of MSL complexes into surrounding chromatin where they roughly double the rates of transcription. We generated many transgenic stocks in which the roX1 gene was moved from its normal location on the X to new autosomal sites. Approximately 10% of such lines displayed unusual sexually dimorphic expression patterns of the transgene's mini-white eye-color marker. Males often displayed striking mosaic pigmentation patterns similar to those seen in position-effect variegation and yet most inserts were in euchromatic locations. In many of these stocks, female mini-white expression was very low or absent. The male-specific activation of mini-white depended upon the MSL complex. We propose that these transgenes are inserted in several different types of repressive chromatin environments that inhibit mini-white expression. Males are able to overcome this silencing through the action of the MSL complex spreading from the roX1 gene and remodeling the local chromatin to allow transcription. The potency with which an ectopic MSL complex overcomes silent chromatin suggests that its normal action on the X must be under strict regulation.

Animals↗

PubMed1973

Terminal synthesis of xanthommatin in Drosophila melanogaster. 3. Mutational pleiotropy and pigment granule association of phenoxazinone synthetase.

Phenoxazinone synthetase, which catalyzes the condensation of 3-hydroxykynurenine to xanthommatin, the brown eye pigment of Drosophila, is shown to exist in association with a particle which resembles the cytologically defined Type I pigment granule. Several classical eye color mutants (v, cn, st, ltd, cd, w), including two which effect other enzymes in the xanthommatin pathway (v, cn), have low levels of phenoxazinone synthetase activity and disrupt the normal association of the enzyme with the pigment granule. A model is proposed depicting several structural and enzymatic interrelationships involved in the developmental control of xanthommatin synthesis in Drosophila.

Amino Acids↗

PubMedDate not supplied

Genetic traits of the mosquito Anopheles gambiae: red stripe, frizzled, and homochromy1.

The expression, inheritance, and linkage relationships of three genetic traits were studied in the malaria vector Anopheles gambiae. Red stripe (Rs) is a common phenotypic polymorphism in numerous A. gambiae populations, whereas frizzled (f) and homochromy1 (hom1) were isolated from (60)Co-irradiated mosquitoes. Red stripe appears as a diffuse stripe of pigment on the dorsum of larvae and pupae and is variable in expressivity and penetrance. Our data demonstrate that Red stripe results from a heterozygous collarless genotype (i.e., c+ c, chromosome 2) and is essentially sex-limited to females. frizzled is a sex-linked recessive semi-lethal identified by deformed lateral larval setae; its lethality manifests as low rates of adult emergence and brief adult survival. frizzled is located on the X chromosome between pink eye and Mosaic, 3 cM from Mosaic and approximately 12 cM from pink eye. Finally, the mutation homochromy1 (hom1) is on chromosome 2 and causes a recessive phenotype that prevents normal darkening of larvae when reared in a black container. Unlike mutants with this characteristic described thus far, the eye color of hom1 mutants is normal. We determined that hom1 is located between Dieldrin resistance and collarless, approximately 3 cM from the latter. We discuss the possibility of differences in male and female recombination values and the range of values that have been observed in test crosses for chromosome 2 markers.

Alleles↗