P-element Research Articles

TheP-element-induced silencing effect ofKPtransposons is dose dependent inDrosophila melanogaster

Transposable elements are found in the genomes of all eukaryotes and play a critical role in altering gene expression and genome organization. In Drosophila melanogaster, transposable P elements are responsible for the phenomenon of hybrid dysgenesis. KP elements, a deletion-derivative of the complete P element, can suppress this mutagenic effect. KP elements can also silence the expression of certain other P-element-mediated transgenes in a process called P-element-dependent silencing (PDS), which is thought to involve the recruitment of heterochromatin proteins. To explore the mechanism of this silencing, we have mobilized KP elements to create a series of strains that contain single, well-defined KP insertions that show PDS. To understand the quantitative role of KP elements in PDS, these single inserts were combined in a series of crosses to obtain genotypes with zero, one, or two KP elements, from which we could examine the effect of KP gene dose. The extent of PDS in these genotypes was shown to be dose dependent in a logarithmic rather than linear fashion. A logarithmic dose dependency is consistent with the KP products interacting with heterochromatic proteins in a concentration-dependent manner such that two molecules are needed to induce gene silencing.

Expression of Drosophila virilis Retroelements and Role of Small RNAs in Their Intrastrain Transposition

Transposition of two retroelements (Ulysses and Penelope) mobilized in the course of hybrid dysgenesis in Drosophila virilis has been investigated by in situ hybridization on polytene chromosomes in two D. virilis strains of different cytotypes routinely used to get dysgenic progeny. The analysis has been repeatedly performed over the last two decades, and has revealed transpositions of Penelope in one of the strains, while, in the other strain, the LTR-containing element Ulysses was found to be transpositionally active. The gypsy retroelement, which has been previously shown to be transpositionally inactive in D. virilis strains, was also included in the analysis. Whole mount is situ hybridization with the ovaries revealed different subcellular distribution of the transposable elements transcripts in the strains studied. Ulysses transpositions occur only in the strain where antisense piRNAs homologous to this TE are virtually absent and the ping-pong amplification loop apparently does not take place. On the other hand small RNAs homologous to Penelope found in the other strain, belong predominantly to the siRNA category (21nt), and consist of sense and antisense species observed in approximately equal proportion. The number of Penelope copies in the latter strain has significantly increased during the last decades, probably because Penelope-derived siRNAs are not maternally inherited, while the low level of Penelope-piRNAs, which are faithfully transmitted from mother to the embryo, is not sufficient to silence this element completely. Therefore, we speculate that intrastrain transposition of the three retroelements studied is controlled predominantly at the post-transcriptional level.

Wheat hybridization and polyploidization results in deregulation of small RNAs.

Speciation via interspecific or intergeneric hybridization and polyploidization triggers genomic responses involving genetic and epigenetic alterations. Such modifications may be induced by small RNAs, which affect key cellular processes, including gene expression, chromatin structure, cytosine methylation and transposable element (TE) activity. To date, the role of small RNAs in the context of wide hybridization and polyploidization has received little attention. In this work, we performed high-throughput sequencing of small RNAs of parental, intergeneric hybrid, and allopolyploid plants that mimic the genomic changes occurring during bread wheat speciation. We found that the percentage of small RNAs corresponding to miRNAs increased with ploidy level, while the percentage of siRNAs corresponding to TEs decreased. The abundance of most miRNA species was similar to midparent values in the hybrid, with some deviations, as seen in overrepresentation of miR168, in the allopolyploid. In contrast, the number of siRNAs corresponding to TEs strongly decreased upon allopolyploidization, but not upon hybridization. The reduction in corresponding siRNAs, together with decreased CpG methylation, as shown here for the Veju element, represent hallmarks of TE activation. TE-siRNA downregulation in the allopolyploid may contribute to genome destabilization at the initial stages of speciation. This phenomenon is reminiscent of hybrid dysgenesis in Drosophila.

Study of the epigenetic regulation of transpositions of nonautonomous P-elements in Drosophila at different temperatures

In a system of Drosophila P-element activation at 25 and 18°C, we observed an increase in the gene conversion frequency among the offspring of parents containing nonautonomous P-elements and a chromosome with the rad201G1 mutation in the genome. A similar increase in conversion events in this system was shown in experiments with the mutation mei41D5. In both cases, inheritance of the increased conversion was also observed among offspring not carrying the rad201G1 or mei41D5 mutations.

Morphologic and molecular manifestations of hybrid dysgenesis in ontogenesis of Drosophila virilis

Disorders of germ track cell development that take place in crossbreeding of certain lines of Drosophila virilis and lead to hybrid dysgenesis (HD) syndrome have been studied. Polar cells and germ line cells were identified with specific antibodies against Vasa protein. It has been shown that abnormalities of formation of primary gonads takes place already at the 11-12 stage of embryo development and the consequences of germ line cell death lead to disorders of gonad development at the following stages of ontogenesis of dysgenic hybrids. The start point of germ line cell death in embryogenesis as well as initiation of transcription of Penelope retroelement, which is supposed to play a significant role in HD syndrome development in D. virilis, were estimated.

Genomic Instability of I Elements of Drosophila melanogaster in Absence of Dysgenic Crosses

Retrotranspostion of I factors in the female germline of Drosophila melanogaster is responsible for the so called I-R hybrid dysgenesis, a phenomenon that produces a broad spectrum of genetic abnormalities including reduced fertility, increased frequency of mutations and chromosome loss. Transposition of I factor depends on cellular conditions that are established in the oocytes of the reactive females and transmitted to their daughters. The so-called reactivity is a cellular state that may exhibit variable levels of expression and represents a permissive condition for I transposition at high levels. Defective I elements have been proposed to be the genetic determinants of reactivity and, through their differential expression, to modulate transposition of active copies in somatic and/or germ line cells. Recently, control of transposable element activity in the germ line has been found to depend on pi-RNAs, small repressive RNAs interacting with Piwi-family proteins and derived from larger transposable elements (TE)-derived primary transcripts. In particular, maternally transmitted I-element piRNAs originating from the 42AB region of polytene chromosomes were found to be involved in control of I element mobility. In the present work, we use a combination of cytological and molecular approaches to study the activity of I elements in three sublines of the inducer y; cn bw; sp isogenic strain and in dysgenic and non-dysgenic genetic backgrounds. Overall, the results of FISH and Southern blotting experiments clearly show that I elements are highly unstable in the Montpellier subline in the absence of classical dysgenic conditions. Such instability appears to be correlated to the amount of 5′ and 3′ I element transcripts detected by quantitative and real-time RT-PCR. The results of this study indicate that I elements can be highly active in the absence of a dysgenic crosses. Moreover, in the light of our results caution should be taken to assimilate the genomic annotation data on transposable elements to all y; cn bw sp sublines.

Drosophila I-Rhybrid dysgenesis is associated with catastrophic meiosis and abnormal zygote formation

The Drosophila I-R type of hybrid dysgenesis is a sterility syndrome (SF sterility) associated with the mobilization of the I retrotransposon in female germ cells. SF sterility results from a maternal-effect embryonic lethality whose origin has remained unclear since its discovery about 40 years ago. Here, we show that meiotic divisions in SF oocytes are catastrophic and systematically fail to produce a functional female pronucleus at fertilization. As a consequence, most embryos from SF females rapidly arrest their development with aneuploid or damaged nuclei, whereas others develop as non-viable, androgenetic haploid embryos. Finally, we show that, in contrast to mutants affecting the biogenesis of piRNAs, SF egg chambers do not accumulate persistent DNA double-strand breaks, suggesting that I-element activity might perturb the functional organization of meiotic chromosomes without triggering an early DNA damage response.

Erratum to: “Dynamics of Hybrid Dysgenesis Frequency in Drosophila melanogaster in Controlled Terms of Protracted Radiation Exposure”

The dynamics of hybrid dysgenesis frequency in F 1 descendants of two lines of Drosophila melanogaster (lines Santon-s and radius incompletus (ri) brining P-mobile element), which was maintained for 20 generations were under the conditions of chronic radiation with three dose rate (1.2 × 10−8; 0.3 × 10−8; 0.12 × 10−8 Gy/s), have been studied. Gradual changes have been shown in the dose dependences of the hybrid dysgenesis frequency for F 1 descendants of every 20 generations from parents exposed to radiation. The complicated dynamics of the transitional process of the appearance of gonadal dysgenesis depending on the duration and dose rate of irradiation in ancestors, has been found. The cumulative effect of the prolonged irradiation appears in the form of adaptation at the lowest dose rate of irradiation and at exhaustion at the highest used dose rate. Problem of the transitional process peculiarities, including the hierarchy of protective and adaptive reactions under the conditions of the chronic irradiation has been discussed.

Ultrastructural and element spectrometric analysis of distraction osteogenesis for reconstruction of cleft palate in rhesus macaque model

To study the ultrastructure and Ca/P element spectrometry of distraction osteogenesis (DO) for reconstruction of cleft palate (CP), so as to explore the osteogenesis and remodeling of new bone in situ. 23 rhesus macaques were operated to establish animal models of CP. 2 monkeys didn't received DO as controls. The other 21 monkeys in experimental group underwent DO to correct both bony and soft tissue defects in palate. The distraction was performed at a rate of 0.8 mm/d, twice a day until the cleft was closed. After fixation for 1, 2, 4, 6, 8, 12, 24 weeks, every 3 animals were sacrificed to get the specimens at the distraction gap. The scanning electron microscopic study and Ca, P elements spectrometric analysis were adopted. There were also two unoperated animals as sham group. After fixation for 1-2 weeks, the distraction gap was full of collagen fibers oriented along vector of distraction. Few trabeculae was seen at the margin area. After fixation for 4-6 weeks, active osteogenesis was presented with new formed bone trabeculae and abundant cellular component. After fixation for 8-12 weeks, the new formed bone became mature and couldn't distinguish from the normal bone. 24 weeks later, the bone between the distraction gap had a similar structure to the normal bone. Elements spectrometric analysis results indicated that in early stage of osteogenesis, the P and S peaks were relatively high while the Ca peak was much lower. During the late stage, the S peak was obviously decreased, and Ca/P ratio increased to normal level as in the empty control group. The CP can be corrected by DO. The new bone between the distraction gap is formed and remodeled through intramembraneous osteogenesis.

Small RNA-based silencing strategies for transposons in the process of invading Drosophila species

Colonization of a host by an active transposon can increase mutation rates or cause sterility, a phenotype termed hybrid dysgenesis. As an example, intercrosses of certain Drosophila virilis strains can produce dysgenic progeny. The Penelope element is present only in a subset of laboratory strains and has been implicated as a causative agent of the dysgenic phenotype. We have also introduced Penelope into Drosophila melanogaster, which are otherwise naive to the element. We have taken advantage of these natural and experimentally induced colonization processes to probe the evolution of small RNA pathways in response to transposon challenge. In both species, Penelope was predominantly targeted by endo-small-interfering RNAs (siRNAs) rather than by piwi-interacting RNAs (piRNAs). Although we do observe correlations between Penelope transcription and dysgenesis, we could not correlate differences in maternally deposited Penelope piRNAs with the sterility of progeny. Instead, we found that strains that produced dysgenic progeny differed in their production of piRNAs from clusters in subtelomeric regions, possibly indicating that changes in the overall piRNA repertoire underlie dysgenesis. Considered together, our data reveal unexpected plasticity in small RNA pathways in germ cells, both in the character of their responses to invading transposons and in the piRNA clusters that define their ability to respond to mobile elements.

Dynamics of hybrid dysgenesis frequency in Drosophila melanogaster in controlled terms of protracted radiation exposure

Dynamics of hybrid dysgenesis frequency in Drosophila melanogaster in controlled terms of protracted radiation exposure

The RNA interference system differently responds to the same mobile element in distant Drosophila species

Hybrid dysgenesis provides a brilliant example of ME mobilization, which causes various mutations and other genetic alterations, including gonadal sterility [5, 6]. Three independent systems of hybrid dysgenesis have been described to date in D. melanogaster, and the above alterations result in each case from activa tion of one ME: P element, I element, or hobo [5–7]. On the other hand, at least six unrelated MEs are mobilized in hybrid dysgenesis in D. virilis [8, 9]. A key role in their mobilization is ascribed to Penelope [10, 11].

Heterochromatin, small RNA and post-fertilization dysgenesis in allopolyploid and interploid hybrids of Arabidopsis.

In many plants, including Arabidopsis, hybrids between species and subspecies encounter postfertilization barriers in which hybrid seed fail to develop, or else give rise to infertile progeny. In Arabidopsis, some of these barriers are sensitive to ploidy and to the epigenetic status of donor and recipient genomes. Recently, a role has been proposed for heterochromatin in reprogramming events that occur in reproductive cells, as well as in the embryo and endosperm after fertilization. 21 nt small interfering RNA (siRNA) from activated transposable elements accumulate in pollen, and are translocated from companion vegetative cells into the sperm, while in the maturing seed 24 nt siRNA are primarily maternal in origin. Thus maternal and paternal genomes likely contribute differing small RNA to the zygote and to the endosperm. As heterochromatic sequences also differ radically between, and within, species, small RNA sequences will diverge in hybrids. If transposable elements in the seed are not targeted by small RNA from the pollen, or vice versa, this could lead to hybrid seed failure, in a mechanism reminiscent of hybrid dysgenesis in Drosophila. Heterochromatin also plays a role in apomixis and nucleolar dominance, and may utilize a similar mechanism.

Oncogenic Product HMGA1a Might Function as an Aberrant Splicing Inducer of Estrogen Receptor [alpha] in Breast Cancer

AbstractEstrogen receptor (ER)-[alpha]46 is known as an important isoform for ER[alpha]. It inhibits the function of full length ER[alpha] in MCF-7 mammary carcinoma cells and associated with cell cycle arrest. On the other hand, the oncogene HMGA1 (formally HMG I/Y) is known to have increased expression in mammary carcinoma correlating with the degree of malignancy. We present here that HMGA1a (HMG I) induces the exon skipped product, ER[alpha]46 mRNA, by tethering U1 snRNP to an upstream pseudo 5' splice site, which is quite analogous to the PSI-mediated splicing regulation of Drosophila P-element.

Epigenetic regulation of Drosophila nonautonomous p-element transpositions at different temperatures of development

In a system of Drosophila P-element activation at 25 °С and 18 °С we observed the increase of the gene conversion frequency among the offspring of parents containing nonautonomous P-elements and a chromosome with rad201supG1/sup mutation in genome. The similar increase of conversion events in this system was shown in the experiments with mutation mei41D5. In both cases inheritance of the increased gene conversion frequency had an epigenetic character, since increased conversion was observed also among the offspring not carrying mutations rad201supG1/sup or mei41D5.

Detection of P element transcripts in embryos of Drosophila melanogaster and D. willistoni

The P element is one of the most thoroughly studied transposable elements (TE). Its mobilization causes the hybrid dysgenesis that was first described in Drosophila melanogaster. While studies of the P element have mainly been done in D. melanogaster, it is believed that Drosophila willistoni was the original host species of this TE and that P was transposed to the D. melanogaster genome by horizontal transfer. Our study sought to compare the transcriptional behavior of the P element in embryos of D. melanogaster, which is a recent host, with embryos of two strains of D. willistoni, a species that has contained the P element for a longer time. In both species, potential transcripts of transposase, the enzyme responsible for the TE mobilization, were detected, as were transcripts of the 66-kDa repressor, truncated and antisense sequences, which can have the ability to prevent TEs mobilization. The truncated transcripts reveal the truncated P elements present in the genome strains and whose number seems to be related to the invasion time of the genome by the TE. No qualitative differences in antisense transcripts were observed among the strains, even in the D. willistoni strain with the highest frequency of heterochromatic P elements.

Cytotype regulation inDrosophila melanogaster: synergism between telomeric and non-telomericPelements

The X-linked telomeric P elements TP5 and TP6 interact synergistically with non-telomeric P elements to repress hybrid dysgenesis. In this repression, the telomeric P elements exert maternal effects, which, however, are not sufficient to establish synergism with the non-telomeric P elements. Once synergism is established, the capacity to repress dysgenesis in the offspring of a cross persists for at least two generations after removing the telomeric P element from the genotype. At the molecular level, synergism between telomeric and non-telomeric P elements is correlated with effective elimination of P-element mRNA in the germ line. Maternally transmitted mutations in the genes aubergine, piwi and Suppressor of variegation 205 [Su(var)205] block the establishment of synergism between telomeric and non-telomeric P elements, and paternally transmitted mutations in piwi and Su(var)205 disrupt synergism that has already been established. These findings are discussed in terms of a model of cytotype regulation of P elements based on Piwi-interacting RNAs (piRNAs) that are amplified by cycling between sense and antisense species.

Cytotype regulation by telomericPelements inDrosophila melanogaster: variation in regulatory strength and maternal effects

Strains carrying the X-linked telomeric P elements TP5 or TP6 varied in their ability to repress hybrid dysgenesis. The rank ordering of these strains was consistent across different genetic assays and was not related to the type of telomeric P element (TP5 or TP6) present. Strong repression of dysgenesis was associated with weak expression of mRNA from the telomeric P element and also with a reduced amount of mRNA from a transposase-producing P element contained within a transgene inserted on an autosome. A strictly maternal component of repression, transmitted independently of the telomeric P element, was detected in the daughters but not the sons of females from the strongest repressing strains. However, this effect was seen only when dysgenesis was induced by crossing these females to males from a P strain, not when it was induced by crossing them to males homozygous for a single transposase-producing P element contained within a transgene. These findings are consistent with the hypothesis that the P cytotype, the condition that regulates P elements, involves an RNA interference mechanism mediated by piRNAs produced by telomeric P elements such as TP5 and TP6 and amplified by RNAs produced by other P elements.

The possible effect of transposons on the Drosophila melanogaster somatic mutation and recombination test

The wing somatic mutation and recombination test (SMART) using transheterozygotes for the Drosophila melanogaster third chromosome markers mwh (multiple wing hairs) and flr 3 (flare-3) has proved to be efficient in genotoxicity screens. The genetic background of the D. melanogaster strains affects the frequency of identification of somatic mutant spots. The genetic background appears to be also of importance in hybrid dysgenesis (HD) revealed in crosses between flies from genetically distant D. melanogaster strains. In this study, we analyzed mwh and flr3/ Ser D. melanogaster strains for the presence of the P and hobo transposable elements that induce genetic instability in P–M and H–E dysgenic crosses, respectively. According to PCR these strains lack the P-element. The mwh strain does not contain the hobo-element too, while hobo is present as a full-length variant and its numerous defective derivatives in the flr 3 / Ser genome. Based on the crosses the reference E- and H-strains to strains used in SMART, the flr/ Ser were assigned to the H-type and the mwh to the E-type. Fluorescence in situ hybridization reveals over 50 hobo hybridization sites scattered throughout the flr 3 / Ser genome. Thus, there is a basis for H–E HD in the strains we studied. However the mwh/ flr 3 , regardless of cross-direction showed higher fertility than the mwh females. Cross-direction had also no affect on hybrid fertility. This meant that they did not exhibit the major HD symptoms. In our view, the significance of the TE activity as a cause of HD has been overestimated, in the case of H–E HD at least. The majority of the mutant spots in SMART result not so much from mutations or TE transposition as from recombination events, even in the case of balancer individuals.

Mutations in many genes affect aggressive behavior in Drosophila melanogaster

BackgroundAggressive behavior in animals is important for survival and reproduction. Identifying the underlying genes and environmental contexts that affect aggressive behavior is important for understanding the evolutionary forces that maintain variation for aggressive behavior in natural populations, and to develop therapeutic interventions to modulate extreme levels of aggressive behavior in humans. While the role of neurotransmitters and a few other molecules in mediating and modulating levels of aggression is well established, it is likely that many additional genetic pathways remain undiscovered. Drosophila melanogaster has recently been established as an excellent model organism for studying the genetic basis of aggressive behavior. Here, we present the results of a screen of 170 Drosophila P-element insertional mutations for quantitative differences in aggressive behavior from their co-isogenic control line.ResultsWe identified 59 mutations in 57 genes that affect aggressive behavior, none of which had been previously implicated to affect aggression. Thirty-two of these mutants exhibited increased aggression, while 27 lines were less aggressive than the control. Many of the genes affect the development and function of the nervous system, and are thus plausibly relevant to the execution of complex behaviors. Others affect basic cellular and metabolic processes, or are mutations in computationally predicted genes for which aggressive behavior is the first biological annotation. Most of the mutations had pleiotropic effects on other complex traits. We characterized nine of these mutations in greater detail by assessing transcript levels throughout development, morphological changes in the mushroom bodies, and restoration of control levels of aggression in revertant alleles. All of the P-element insertions affected the tagged genes, and had pleiotropic effects on brain morphology.ConclusionThis study reveals that many more genes than previously suspected affect aggressive behavior, and that these genes have widespread pleiotropic effects. Given the conservation of aggressive behavior among different animal species, these are novel candidate genes for future study in other animals, including humans.