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The corrosion resistance and influence mechanism of P in low-Ni Cu-P-Cr-Ni weathering steels were analyzed by wet/dry cyclic corrosion and electrochemical tests. The electrochemical experiment results showed that the corrosion potential and impedance of weathering steels were all more positive than that of ordinary Q345B carbon steel. Compared to Cu-0.02P-Cr-Ni steel, however, the corrosion current density of Cu-0.07P-Cr-Ni steel was higher. After 72 h wet/dry cyclic corrosion tests, the corrosion resistances of the two weathering steels were nearly identical but better than that of Q345B steel. The effect of P was particularly significant in the initial stage of corrosion. Phosphates (PO43−) were formed from P, which improved the corrosion current density and promoted the rapid formation of a rust layer. After 72 h wet/dry cyclic corrosion tests, the matrix was further protected by the enrichment of Cu and Cr, which existed as Cu+ and Cr3+, respectively. The P content did not significantly affect the corrosion resistance of weathering steels after 72 h wet/dry cyclic corrosion tests. Therefore, the P content can be lowered to reduce the cold brittleness in low-Ni Cu-P-Cr-Ni weathering steels. [ABSTRACT FROM AUTHOR]

Using the FISH method and PCR analysis, the presence of canonical P element was studied in the genomes of a number of laboratory lines isolated from nature in different years from the Zaprionus genus ( Z. indianus) and Drosophila genus, Sophophora subgenus ( D. ananassae, D. eugracilis, D. simulans, D. immigrans), Drosophila subgenus ( D. virilis, D. mercatorum, D. hydei, D. funebris, D. pseudoobscura), Lordiphosa subgenus ( L. magnipectinata), and Dorsilopha subgenus ( D. busckii) in a search for new cases of horizontal transfer. According to our data, the L. magnipectinata genome contains sequences homologous to terminal regions of canonical P element, as well as the sequence with a weak homology from the central part of canonical P element. The P-element hybridization sites adjacent to the chromocenter were found in the D. pseudoobscura genome; this can indicate an ancient origin of the sequences homologous to the P element. The P element is absent in old D. simulans lines, except for the line isolated from nature in 2014 (in which the P element was found); this confirms data of other researchers about recent cases of horizontal P-element transfer in this species. No new cases of horizontal transfer were detected in the analyzed lines. [ABSTRACT FROM AUTHOR]

Intraspecific hybrid dysgenesis (HD) appears after some strains of D. melanogaster are crossed. The predominant idea is that the movement of transposable P elements causes HD. It is believed that P elements appeared in the D. melanogaster genome in the middle of the last century by horizontal transfer, simultaneously with the appearance of HD determinants. A subsequent simultaneous expansion of HD determinants and P elements occurred. We analyzed the current distribution of HD determinants in natural populations of D. melanogaster and found no evidence of their further spread. However, full-sized P elements were identified in the genomes of all analyzed natural D. melanogaster strains independent of their cytotypes. Thus, the expansion of P elements does not correlate with the expansion of HD determinants. We found that the ovaries of dysgenic females did not contain germ cells despite the equal number of primordial germ cells in early stages in dysgenic and non-dysgenic embryos. We propose that HD does not result from DNA damage caused by P element transposition, but it would be the disruption in the regulation of dysgenic ovarian formation that causes the dysgenic phenotypes. [ABSTRACT FROM AUTHOR]

Let X be a convex curve in the plane (say, the unit circle), and let $${\mathcal {S}}$$ be a family of planar convex bodies such that every two of them meet at a point of X. Then $${\mathcal {S}}$$ has a transversal $$N\subset {\mathbb {R}}^2$$ of size at most $$1.75\times 10^9$$ . Suppose instead that $${\mathcal {S}}$$ only satisfies the following '( p, 2)-condition': Among every p elements of $${\mathcal {S}}$$ , there are two that meet at a common point of X. Then $${\mathcal {S}}$$ has a transversal of size $$O(p^8)$$ . For comparison, the best known bound for the Hadwiger-Debrunner ( p, q)-problem in the plane, with $$q=3$$ , is $$O(p^6)$$ . Our result generalizes appropriately for $${\mathbb {R}}^d$$ if $$X\subset {\mathbb {R}}^d$$ is, for example, the moment curve. [ABSTRACT FROM AUTHOR]

The transposons of Drosophila melanogaster are regulated by small RNAs that interact with the Piwi family of proteins. These piRNAs are generated from transposons inserted in special loci such as the telomere-associated sequences at the left end of the X chromosome. Drosophila's P transposons can also be regulated by a polypeptide encoded by the KP element, a 1.15-kb-long member of the P family. Using piRNA-generating telomeric P elements ( TPs) and repressor-producing transgenic KP elements, we demonstrate a functional connection between these two modes of regulation. By themselves, the TPs partially repress gonadal dysgenesis, a trait caused by rampant P-element activity in the germ line. This repression is manifested as a strictly maternal effect arising from the cytoplasmic transmission of P-specific piRNAs from mother to offspring. The repression is enhanced by genetic interactions between the TPs and other, non-telomeric P elements-a phenomenon attributable to ping-pong amplification of maternal piRNAs. KP elements, like other kinds of non-telomeric P elements, enhance regulation anchored in the TPs. However, with some TPs, the enhanced regulation is manifested as a strictly zygotic effect of the KP element. This effect is seen when the TP has few sequences in common with the KP element, a condition not conducive to ping-pong amplification of piRNAs; it can be attributed to the action of the KP repressor polypeptide. Because the effect is seen only when a TP was present in the mother's genotype, maternally generated P-element piRNAs could facilitate regulation by the KP repressor polypeptide. [ABSTRACT FROM AUTHOR]

P element is a DNA transposon, known to spread in genome using transposase activity. Its activity is tissue-specific and normally observed at high temperatures within 24°C to 29°C. Here, we present a predicted RNA secondary structure domain of P element pre-mRNA which could potentially regulate the temperature sensitivity of the P element activity. In canonical P elements, the structure is a small hairpin with double-helical part interrupted by a symmetric loop and a mismatch. In M type P elements, the A.A mismatch is substituted by an A-U base pair, stabilizing the structure. The hairpin structure covers the region involving the IVS-3 5′ splice site and both pseudo-splice sites F1 and F2. While the IVS-3 and F1 binding sites of U1 snRNA are located in the double-stranded part of the structure, the F2 site is exposed in the hairpin loop. The formation of this structure may interfere with landing of U1 snRNA on IVS-3 site, while F2 is positioned for the interaction. Alignment of P element sequences supports the proposed existence of the hairpin, showing high similarity for this region. The hairpin structure, stable at low temperatures, may prevent correct IVS-3 splicing. Conversely, temperature-induced destabilization of the hairpin structure may result in the splicing at the proper IVS-3 splice site. Taking into account the increasing amount of data demonstrating the important influence of RNA folding on phenotypes determined by alternative splicing a model for possible regulation of the activity of mobile elements by pre-mRNA secondary structure seems intriguing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper explores the previously undiscussed phenomenon of preposition doubling in Flemish Dutch dialects. It offers an account for the properties of this phenomenon adapting the basic internal structures for Dutch PPs proposed by Koopman and Den Dikken . They argue following Van Riemsdijk (, ) that PPs contain functional structure, parallel to the verbal and nominal domain: the lexical P is dominated by a PlaceP-parallel to vP-and also a DegP, hosting degree modifiers, and a CP. We argue that doubling PPs are the result of identical spell-out of a locative P-element (P) and a directional P-element (P), in a structure in which P has a full extended projection but P does not. The CP in the functional layer of P in doubling PPs is defective, which derives doubling as well as the distribution of R-words in these PPs. C's defectivity also provides a window on the cross-dialectal distribution of P-doubling: the availability of P-doubling in certain dialects is correlated with the use of the directional preposition van 'of, from' as the introducer of infinitival clauses exhibiting NP-raising. [ABSTRACT FROM AUTHOR]

When experimental P + M populations were exposed to chronic γ-irradiation (0.31 mGy/h), the highest instability level of the singed-weak ( sn) locus was observed in F-F with a subsequent decrease and stabilization of the mutation rate. The sn mutation rate was within the range of spontaneous variation in conditions of P-M hybrid dysgenesis and irradiation of males of the Harwich laboratory strain with active P elements at 1.61 mGy/h. The instability of the sn locus was significantly higher at lower dose rates (0.23 and 0.31 mGy/h), suggesting a nonlinear dose-effect relationship. [ABSTRACT FROM AUTHOR]

The P elements of Drosophila melanogaster are well-studied transposons with both mobilizing and repressor functions . P elements can also variably silence the expression of certain other transgenes through a phenomenon known as P element-dependent silencing (PDS). To examine the role of the P repressor in PDS, we have induced, isolated, and characterized 22 point mutations in an archetype P element called P[SalI]89D. All mutations showed a loss in the ability to silence one or more assays for the PDS phenotype. These mutants also lost the ability to induce the suppression of variegation in P[hsp26-pt-T]39C-12, another P element-dependent phenotype. A subgroup of 11 mutations was further assayed for their ability to act as a P repressor and silence the P element promoter transcribing a lacZ gene, and this function was lost as well. Taken together, this study supports a model of PDS acting through protein interactions, not RNA, with heterochromatic proteins to modify the extent of variegation seen in PDS. Furthermore, the common loss of functions for PDS and P repressor silencing (from another P promoter) argues for a common role of the repressor. This makes the PDS model a good system for examining P repressor functions and how they relate to transposon-mediated gene silencing in general. [ABSTRACT FROM AUTHOR]

RNA editing is proposed as a modulator of transcriptomes, but its biological impact has not been fully elucidated. In particular, its importance for transposable elements is controversial. We found RNA editing on antisense read-through transcripts of KP elements, one of the deletion derivatives of P transposable elements in Drosophila melanogaster. Three kinds of RNA editing were detected at 20 sites around the terminal inverted repeats (TIR); 15 A-to-G, four U-to-C, and one C-to-U conversions. A-to-G conversions are suggested to be attributed to A-to-I RNA editing on KP element RNAs, because inosine (I) in RNA is recognized as G by reverse transcriptase. TIRs were deduced to form dsRNAs as a putative target of ADAR. This is the first report of RNA editing on mobile elements of Drosophila. [ABSTRACT FROM AUTHOR]

P elements, both complete and incomplete, contain a left and right end, normally depicted as pointing away from each other. Here, we examine the properties of P elements that may be described as ‘re-arranged elements’ or ‘inside-out elements’, containing inverted ends. Two such structures exist, having either ends pointing towards each other, ‘head-to-head or H–H’, or ends pointing in the same direction ‘head-to-tail or H–T’. We show that both structures are unstable in the presence of P element transposase. For the H–H element there is a high frequency of deletion of the intervening material and almost exact rejoining of element ends with the 4 bp CATG palindromic end sequence shared by the two element ends. This result is predicted by the Beall and Rio model of P element excision. For the H–T element there is a high frequency of exact excision of the entire inverted right-end, a result again predicted by the Beall and Rio model. Both structures lead to recombination in the way expected from a normal element. The rates of recombination are, however, much lower than might be expected from the organization of ends, a result that can be explained in terms of the low likelihood of insertion into a chromosomal region lacking another P element end. We also investigate the properties of combinations of re-arranged and normal elements, and show that there is a directionality property when left and right ends are combined in trans that can be explained in terms of strand repair.Heredity (2009) 102, 342–348; doi:10.1038/hdy.2009.1; published online 28 January 2009 [ABSTRACT FROM AUTHOR]

During Drosophila aging mortality rate increases exponentially and progeny production per animal declines dramatically, correlating with decreased number and division of somatic and germ-line stem cells in the gonads. To search for genes that might promote both longevity and fecundity, a P element transposon ( PdL), containing an outwardly directed, doxycycline-inducible promoter was used to generate conditional mutations. Mutant females were screened for increased fecundity at late ages in the presence of doxycycline. Two genes were identified, named hebe (CG1623) and magu (CG2264), that when over-expressed in adult flies could increase life span by ~5–30% in both sexes and increase female fecundity at late ages. Transcripts for magu are enriched in the Drosophila stem cell niche region, and magu encodes a protein related to the human SMOC2 regulator of angiogenesis. While moderate over-expression of magu in adult females increased fecundity at late ages, high-level over-expression of magu was maternal-effect lethal. The data demonstrate that adult-specific over-expression of hebe and magu can increase life span and modulate female fecundity, and provide further evidence against obligatory trade-offs between reproduction and longevity. [ABSTRACT FROM AUTHOR]

P elements are thought to replicate themselves starting with the association of the left and right ends, followed by a cut–copy–paste process. An abnormal form of this process has been shown to occur when the associated left and right ends come from sister elements rather than from the same element, leading to formation of a ‘hybrid element.’ These ends can insert nearby in the genome to produce recombination, with associated structural changes. We have previously increased the frequency of such ‘hybrid element insertion’ by combining end-deleted elements in trans in a genotype with a left-end on one chromosome and a right-end on the homologous chromosome. Although many recombinants produced by this genotype have structural changes expected with insertion, nearly 50% of the predicted insertional recombinants contain no structural change. We present evidence using RFLP markers closely linked to the end-deleted elements that in these cases the P element ends dissociate before insertion, and are subsequently ligated together following a process analogous to synthesis-dependent strand annealing. The results suggest that broken ends containing P elements are resolved by the same repair process as ends not containing P elements, and that such repair from hybrid element events may occur in the majority of cases.Heredity (2009) 102, 127–132; doi:10.1038/hdy.2008.87; published online 10 September 2008 [ABSTRACT FROM AUTHOR]

We have studied the molecular characteristics of the yellow locus (y; 1–0.0), which determines the body color of phenotypically wild-type and mutant alleles isolated in different years from geographically distant populations of Drosophila melanogaster. According to the Southern blot, data restriction maps of the yellow locus of all examined strains differ from one another, as well as from Oregon stock. FISH analysis shows that, in the neighborhood of the yellow locus in the X chromosome, neither P nor hobo elements are found in y1–775 stock, while only hobo is found in these region in y1–859 and y1–866 stocks, only the P element is found in y+sn849 stock, and both elements are found in y1–719 stock. Thus, all yellow mutants studied are of independent origin. Locus yellow located on the end of X chromosome (region 1A5–8 on the cytologic map) carries significantly more transposon than retrotransposon induced mutations compared to the white locus (region 3C2). It is possible that, at the ends of Drosophila melanogaster chromosomes, transposons are more active than retrotransposons. [ABSTRACT FROM AUTHOR]

Molecular domestication of a transposable element is defined as its functional recruitment by the host genome. To date, two independent events of molecular domestication of the P transposable element have been described: in the Drosophila obscura species group and in the Drosophila montium species subgroup. These P neogenes consist of stationary, nonrepeated sequences, potentially encoding 66-kDa repressor-like (RL) proteins. Here we investigate the function of the montium P neogenes. We provide evidence for the presence of RL proteins in two montium species ( D. tsacasi and D. bocqueti) specifically expressed in adult and larval brain and gonads. We tested the hypothesis that the montium P neogenes’ function is related to the repression of the transposition of distantly related mobile P elements which coexist in the genome. Our results strongly suggest that the montium P neogenes are not recruited to downregulate the P element transposition. Given that all the proteins encoded by mobile or stationary P homologous sequences show a strong conservation of the DNA binding domain, we tested the capacity of the RL proteins to bind DNA in vivo. Immunostaining of polytene chromosomes in D. melanogaster transgenic lines strongly suggests that montium P neogenes encode proteins that bind DNA in vivo. RL proteins show multiple binding to the chromosomes. We suggest that the property recruited in the case of the montium P neoproteins is their DNA binding property. The possible functions of these neogenes are discussed. [ABSTRACT FROM AUTHOR]

Up to now, investigations of expression and regulation of P transposable element have been almost exclusively carried out with the Drosophila melanogaster canonical P element. Analyzing eight species of the saltans group, we detected transposase mRNA in germline tissues of D. saltans and D. prosaltans and repressor mRNA in somatic tissues of D. saltans and D. sturtevanti. Sequencing analysis suggested that these transcripts might belong to the canonical subfamily and that they can be transpositionally active only in D. saltans. dN and dS values of Adh and the P element suggested that the sequences found in D. saltans and D. prosaltans might have been present in the ancestor of the saltans subgroup and that the sequence found in D. sturtevanti might have been horizontally transferred from D. saltans. [ABSTRACT FROM AUTHOR]

Autonomous P elements, inserted in heterochromatic telomeric associated sequences (TAS) at the X chromosome telomere (site 1A) have strong P element regulatory properties that include repression of P-induced hybrid-dysgenesis and of P-lacZ expression in the germline. P-lacZ insertions or defective P elements at 1A in TAS can also repress in trans a euchromatic P-lacZ in the germline. This property has been called a trans-silencing effect (TSE). It requires some sequence-homology between the telomeric insertion and the euchromatic transgene. When repression is partial, variegating lacZ expression is observed, suggesting a chromatin-based component. TSE is observed only when the silencer transgenes are maternally inherited and occurs only in the female germline. We have evidence that this silencing also works in the presence of homologous non- P element sequences suggesting that homology-dependent silencing could be a general phenomenon in the female germline; such a system might have been subsequently adopted by the P element family, allowing its own repression. [ABSTRACT FROM AUTHOR]

In order to study P element dynamics in natural populations of Drosophila melanogaster, 126 isofemale lines were examined from seven of the southernmost islands of Japan (the Sakishima Islands) and from Taiwan. Gonadal dysgenesis (GD) tests showed large divergences in the P-M phenotypes (P inducing and P repressing abilities) between the island populations. The P-M characteristics of each population, however, had not greatly changed in the past 15 years. Their genomic P element profiles are highly similar, consisting mostly of full-size P and of KP elements. We found no clear relationship between phenotype and genomic P element composition. [ABSTRACT FROM AUTHOR]

rid=""id=""Correspondence to: E. HaringAbstract.P elements of two different subfamilies designated as M- and O-type are thought to have invaded host species in the Drosophila obscura group via horizontal transmission from external sources. Sequence comparisons with P elements isolated from other species suggested that the horizontal invasion by the O-type must have been a rather recent event, whereas the M-type invasion should have occurred in the more distant past. To trace the phylogenetic history of O-type elements, additional taxa were screened for the presence of O- and M-type elements using type-specific PCR primers. The phylogeny deduced from the sequence data of a 927-bp section (14 taxa) indicate that O-type elements have undergone longer periods of regular vertical transmission in the lineages of the saltans and willistoni groups of Drosophila. However, starting from a species of the D. willistoni group they were transmitted horizontally into other lineages. First the lineage of the D. affinis subgroup was infected, and finally, in a more recent wave of horizontal spread, species of three different genera were invaded by O-type elements from the D. affinis lineage: Scaptomyza, Lordiphosa, and the sibling species D. bifasciata/D. imaii of the Drosophila obscura subgroup. The O-type elements isolated from these taxa are almost identical (sequence divergence <1%). In contrast, no such striking similarities are observed among M-type elements. Nevertheless, the sequence phylogeny of M-type elements is also not in accordance with the phylogeny of their host species, suggesting earlier horizontal transfer events. The results imply that P elements cross species barriers more frequently than previously thought but require a particular genomic environment and thus seem to be confined to a rather narrow spectrum of host species. Consequently, different P element types acquired by successive horizontal transmission events often coexist within the same genome. [ABSTRACT FROM AUTHOR]

Transposable elements are short but complex pieces of DNA or RNA containing a streamlined minimal-genome with the capacity for its selfish replication in a foreign genomic environment. Cis-regulatory sections within the elements orchestrate tempo and mode of TE expression. Proteins encoded by TEs mainly direct their own propagation within the genome by recruitment of host-encoded factors. On the other hand, TE-encoded proteins harbor a very attractive repertoire of functional abilities for a cell. These proteins mediate excision, replication and integration of defined DNA fragments. Furthermore, some of these proteins are able to manipulate important host factors by altering their original function. Thus, if the host genome succeeds in domesticating such TE-encoded proteins by taming their ‘anarchistic behavior,’ such an event can be considered as an important evolutionary innovation for its own benefit. In fact, the domestication of TE-derived cis-regulatory modules and protein coding sections took place repeatedly in the course of genome evolution. We will present prominent cases that impressively demonstrate the beneficial impact of TEs on host biology over evolutionary time. Furthermore, we will propose that molecular domestication might be considered as a resumption of the same evolutionary process that drove the transition from ‘primitive genomes’ to ‘modern’ ones at the early dawn of life, that is, the adaptive integration of a short piece of autonomous DNA into a complex regulatory network. [ABSTRACT FROM AUTHOR]

As part of our effort to monitor changes in the clinal pattern of P element-associated traits in eastern Australian Drosophila melanogaster, we investigated the genomic P elements of 293 isofemale lines collected in the period 1991–1994 from 45 localities. P elements were present in many copies in all genomes examined, with full-size P and KP element size classes accounting for the large majority. SR elements were not present in at least 92% of the lines tested. South of about 26° south Latitude (°SLat), the ratio of KP to full-size P elements (KP/P ratio) increased, correlating weakly with the P-M phenotypes of the populations, from moderately P populations (26–29°SLat) to M populations (37–38°SLat) North of 26°SLat, in weak P populations, the KP/P ratio was higher than between 26 and 29°Slat. The KP/P ratio appears to be higher in the northern populations than it was when previous studies were done. Overall, a high KP/P ratio among lines correlated roughly with a lack of P activity, but it also correlated with reduced repressor function. In a sample of 30 lines, a maternal effect of repressor function did not show a pattern with latitude, nor with KP/P ratio, nor with presence or absence of P activity. [ABSTRACT FROM AUTHOR]

The effects of interactions between P element and yellow regulatory sequences on the control of yellow expression were studied. The y mutations used in the analysis lack a segment of upstream sequence that extends from position −146 bp to −70 bp, relative to the transcription start site of the yellow gene. This sequence has been found to be necessary for the function of the yellow promoter. The insertion of one or two P element copies at position −69 bp compensates for the deletion in the regulatory region and restores yellow expression. After mobilization of the P element, new phenotypes were selected and molecularly characterized. Two regions in the 5′ part of the P element, from 23 bp to 71 bp and from 82 bp to 108 bp, can each partially compensate for the yellow deletion. In addition, deletion derivatives of the P element were themselves able to activate yellow transcription. All such P elements retain at least 108 bp of sequence at the 5′ end and 15–17 bp at the 3′ end. Thus, the region of the P element from 23 bp to 108 bp contains cis-regulatory elements that can influence the transcription of neighboring genes. [ABSTRACT FROM AUTHOR]

Large inserts have been found to appear within the yellow ( y) locus of several unstable mutant lines derived from a parental strain ( y sc w) of Drosophila melanogaster. The inserts of the individual mutant lines correspond roughly to a series of multimers (4.1, 7.1, 14.3 and 28.9 kbp, respectively) and are always located at the same position, somewhat upstream of the y gene transcription start site. Each of them begins and ends with a l-kbp sequence which shares restriction sites with P elements. One of these inserts (14.3 kbp) has been partially sequenced (1270 bp from the 5′ end). The first 1185 bp match exactly the sequence of an internally deleted P element. The remaining part of the sequence, on the other hand, is unrelated to P elements. It is assumed that large DNA sequences may be captured by the flanking P-element fragments and inserted into new chromosomal sites. [ABSTRACT FROM AUTHOR]

The latitudinal cline in P transposable element-associated characteristics in eastern Australian populations of Drosophila melanogaster has changed between 1986 and 1991–1994. New collections were made in 1991–1994 from localities along the eastern coast of Australia. P element-associated properties of 256 isofemale lines from 43 localities were evaluated using gonadal dysgenesis and/or singed-weak hypermutability assays. The overall results indicate that both P activity and P susceptibility have declined, with all populations showing a tendency towards a state with little P activity potential but with P repressor function (neutral or ‘Q’). P repressor function is strong in all populations except some of the most southerly. P activity potential peaks at about 27° SLat, and drops off to the south (as in 1983–1986 collections) and to the north (in contrast to 1983–1986 collections); thus the cline is no longer a simple P-to-Q-to-M pattern from north to south, but is now Q-P-Q-M. A mtDNA RFLP that putatively distinguishes North American and European populations varies in frequency among the populations but the frequency does not vary clinally with latitude, ruling out massive introductions from North America and Europe as causing the cline. [ABSTRACT FROM AUTHOR]

The phylogenetic distribution of transposable families, P, gypsy, hobo, I, and mariner has been analyzed in 33 species of 11 groups of neotropical Drosophila and a Drosophilidae species Zygotrica vittimaculosa, using squash blot and dot blot. Genomic DNA of almost all neotropical species tested hybridized with gypsy probe and some species showed a particularly strong hybridization signal, as D. gaucha, D. virilis, and species of flavopilosa group. The hobo element was restricted to melanogaster group and some strains of D. willistoni. Only D. simulans DNA showed hybridization to mariner probe in all species tested and D. simulans and D. melanogaster showed hybridization with I element probe. P element homologous sequence was present in D. melanogaster and all species and strains of the willistoni and saltans groups tested. The presence of at least one P-homologous sequence was detected in Drosophila mediopunctata. This one was the only P-bearing species of all six tested from the tripunctata group. Four different pairs of primers homologous to segments of the canonical sequence of D. melanogaster's P were used to amplify specific sequences from D. mediopunctata DNA, showing the occurrence of seemingly well-conserved P-homologous sequences. [ABSTRACT FROM AUTHOR]

Transposable elements are ubiquitous in all organisms and represent a dynamic component of their genomes, causing mutations and thereby genetic variation. Because of their independent and expansive replication strategy, these elements are called selfish and were thought to have no impact on the adaptive evolution of their host organisms. Although most TE-induced mutations seem to exert only negative effects on the fitness of their carrier, recent evidence indicates that in the course of evolution at least some TE-mediated changes have become established features of the host genome. For example, the insertion of TEs may provide novel cis-regulatory regions to preexisting host genes or TE-derived trans-acting factors may undergo a molecular transition into novel host genes through a process described as molecular domestication. The stationary P element related gene clusters of D. guanche, D. madeirensis and D. subobscura provide an excellent model system to study the evolutionary impact of TEs on genome evolution. Each cluster unit consists of a cis-regulating section composed of different insertion sequences followed by the first three exons of a P element that are coding for a 66 kDa ‘repressor-like’ protein. [ABSTRACT FROM AUTHOR]

In Drosophila melanogaster, crossing males carrying autonomous P elements with females devoid of P copies results in hybrid dysgenesis in the germline of progeny. The reciprocal cross produces non-dysgenic progeny due to a maternally inherited state non-permissive for P transposition. The capacity of a P copy to repress transposition depends on both its structure and its chromosomal location. Naturally occuring regulatory P elements inserted at the telomere of the X chromosome have been genetically isolated in a genomic context devoid of other P elements. One or two copies of autonomous P elements at this site (1A) are sufficient to elicit a strong P repression in the germline. These elements are flanked by Telomeric Associated Sequences, previously identified and described by Karpen and Spradling (1992) as having heterochromatic properties. The regulatory properties of P elements at 1A are strongly impaired by mutations affecting Su(var)205, which encodes Heterochromatin Protein 1, a non-histone heterochromatin protein. The regulatory properties of classical P strains are not sensitive to Su(var)205. Models based on chromatin structure or on nuclear localisation of the telomeres are discussed in order to explain both the strong regulatory properties of P elements at the X chromosome telomere and their sensitivity to Su(var)205. [ABSTRACT FROM AUTHOR]

Six highly inbred lines of Drosophila melanogaster extracted from an M′ strain (in the P/M system of hybrid dysgenesis) were studied for the evolution of the number and chromosomal location of complete and defective P elements through generations 52-200. These lines possessed full-sized P elements but differed in their cytotype (M or P). Three lines with P cytotype and full-sized P elements at site 1A had a constant P copy number over generations with low rates of insertion and excision. Three lines with M cytotype and at least one full-sized P element accumulated P copies over the generations and reached a plateau near generation 196, at which rates of transposition and excision were equal to 1.2 × 10 to 3 × 10 events per element per generation. At that time these three lines still presented an M cytotype, produced transposase, and were able to regulate P copy number. The similarity at equilibrium between insertion and excision rates was exactly what was expected from theoretical models for a self-regulated element. The large number of generations necessary to attain the equilibrium in copy number indicates, however, that caution may be de rigueur when testing theoretical models of copy-number containment based on transposition and excision-rate comparison. [ABSTRACT FROM AUTHOR]

The introduction of cloned and manipulated genetic material into the germline of an experimental organism is one of the most powerful tools of modern biology. In the case of the fruit fly, Drosophila melanogaster, there is also an unparalleled range of sophisticated genetic tools to facilitate subsequent analysis. In consequence, Drosophila remains a most favourable model organism for the dissection of gene structure and function in vivo. In this review we look at some of the achievements to date in Drosophila genome manipulation, and at what may be possible in the near future. [ABSTRACT FROM AUTHOR]