Is the evolutionary history of the O-type P element in the saltans and willistoni groups of Drosophila similar to that of the canonical P element?

We studied the occurrence of O-type P elements in at least one species of each subgroup of the saltans group, in order to better understand the phylogenetic relationships among the elements within the saltans group and with those of species belonging to the willistoni group. We found that the O-type subfamily has a patchy distribution within the saltans group (it does not occur in D. neocordata and D. emarginata), low sequence divergence among species of the saltans group as well as in relation to species of the willistoni group, a lower rate of synonymous substitution for coding sequences compared to Adh, and phylogenetic incongruities. These findings suggest that the evolutionary history of the O-type subfamily within the saltans and willistoni groups follows the same model proposed for the canonical subfamily of P elements, i.e., events of horizontal transfer between species of the saltans and willistoni groups.

Copy number of P elements, KP/full-sized P element ratio and their relationships with environmental factors in Brazilian Drosophila melanogaster populations

The P transposable element copy numbers and the KP/full-sized P element ratios were determined in eight Brazilian strains of Drosophila melanogaster. Strains from tropical regions showed lower overall P element copy numbers than did strains from temperate regions. Variable numbers of full-sized and defective elements were detected, but the full-sized P and KP elements were the predominant classes of elements in all strains. The full-sized P and KP element ratios were calculated and compared with latitude. The northernmost and southernmost Brazilian strains showed fewer full-sized elements than KP elements per genome, and the strains from less extreme latitudes had many more full-sized P than KP elements. However, no clinal variation was observed. Strains from different localities, previously classified as having P cytotype, displayed a higher or a lower proportion of KP elements than of full-sized P elements, as well as an equal number of the two element types, showing that the same phenotype may be produced by different underlying genomic components of the P-M system.

Geographic polymorphism of P element in populations of Drosophila sturtevanti

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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

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

Testing transposable elements as genetic drive mechanisms using Drosophila P element constructs as a model system

The use of transposable elements (TEs) as genetic drive mechanisms was explored using Drosophila melanogaster as a model system. Alternative strategies, employing autonomous and nonautonomous P element constructs were compared for their efficiency in driving the ry(+) allele into populations homozygous for a ry(-) allele at the genomic rosy locus. Transformed flies were introduced at 1%, 5%, and 10% starting frequencies to establish a series of populations that were monitored over the course of 40 generations, using both phenotypic and molecular assays. The transposon-borne ry(+) marker allele spread rapidly in almost all populations when introduced at 5% and 10% seed frequencies, but 1% introductions frequently failed to become established. A similar initial rapid increase in frequency of the ry(+) transposon occurred in several control populations lacking a source of transposase. Constructs carrying ry(+) markers also increased to moderate frequencies in the absence of selection on the marker. The results of Southern and in situ hybridization studies indicated a strong inverse relationship between the degree of conservation of construct integrity and transposition frequency. These finding have relevance to possible future applications of transposons as genetic drive mechanisms.

P element insertion-dependent gene activation in the Drosophila eye

Insights into the function of a gene can be gained in multiple ways, including loss-of-function phenotype, sequence similarity, expression pattern, and by the consequences of its misexpression. Analysis of the phenotypes produced by expression of a gene at an abnormal time, place, or level may provide clues to a gene’s function when other approaches are not illuminating. Here we report that an eye-specific, enhancer–promoter present in the P element expression vector pGMR is able to drive high level expression in the eye of genes near the site of P element insertion. Cell fate determination, differentiation, proliferation, and death are essential for normal eye development. Thus the ability to carry out eye-specific misexpression of a significant fraction of genes in the genome, given the dispensability of the eye for viability and fertility of the adult, should provide a powerful approach for identifying regulators of these processes. To test this idea we carried out two overexpression screens for genes that function to regulate cell death. We screened for insertion-dependent dominant phenotypes in a wild-type background, and for dominant modifiers of a reaper overexpression-induced small eye phenotype. Multiple chromosomal loci were identified, including an insertion 5′ to hid, a potent inducer of apoptosis, and insertions 5′ to DIAP1, a cell death suppressor. To facilitate the cloning of genes near the P element insertion new misexpression vectors were created. A screen with one of these vectors identified eagle as a suppressor of a rough eye phenotype associated with overexpression of an activated Ras1 gene.

Susceptibility of two karyotypic forms of Anopheles aconitus (Diptera: Culicidae) to Plasmodium falciparum and P. vivax

Four laboratory-raised colonies of two karyotypic forms of Anopheles aconitus, i.e., Form B (Chiang Mai and Phet Buri strains) and C (Chiang Mai and Mae Hong Son strains), were experimentally infected with Plasmodium falciparum and P. vivax using an artificial membrane feeding technique and dissected eight and 12 days after feeding for oocyst and sporozoite rates, respectively. The results revealed that An. aconitus Form B and C were susceptible to P. falciparum and P. vivax, i.e., Form B (Chiang Mai and Phet Buri strains/P. falciparum and P. vivax) and Form C (Chiang Mai and Mae Hong Son strains/P. vivax). Comparative statistical analyses of the oocyst rates, average number of oocysts per infected midgut and sporozoite rates among all strains of An. aconitus Form B and C to the ingroup control vectors, An. minimus A and C, exhibited mostly no significant differences, confirming the high potential vector of the two Plasmodium species. The sporozoite-like crystals found in the median lobe of the salivary glands, which could be a misleading factor in the identification of true sporozoites in salivary glands were found in both An. aconitus Form B and C.

A phylogenetic perspective on P transposable element evolution in Drosophila

The P element, originally described in Drosophila melanogaster, is one of the best-studied eukaryotic transposable elements. In an attempt to understand the evolutionary dynamics of the P element family, an extensive phylogenetic analysis of 239 partial P element sequences has been completed. These sequences were obtained from 40 species in the Drosophila subgenus Sophophora. The phylogeny of the P element family is examined in the context of a phylogeny of the species in which these elements are found. An interesting feature of many of the species examined is the coexistence in the same genome of P sequences belonging to two or more divergent subfamilies. In general, P elements in Drosophila have been transmitted vertically from generation to generation over evolutionary time. However, four unequivocal cases of horizontal transfer, in which the element was transferred between species, have been identified. In addition, the P element phylogeny is best explained in numerous instances by horizontal transfer at various times in the past. These observations suggest that, as with some other transposable elements, horizontal transfer may play an important role in the maintenance of P elements in natural populations.

Susceptibility to the anticoagulants bromadiolone and coumatetralyl in wild Norway rats (Rattus norvegicus) from the UK and Germany

A new blood clotting response test was used to determine the susceptibility, to coumatetralyl and bromadiolone, of laboratory strains of Norway rat from Germany and the UK (Hampshire), and wild rats trapped on farms in Wales (UK) and Westphalia (Germany). Resistance factors were calculated in relation to the CD strain of Norway rat. An outbred strain of wild rats, raised from rats trapped in Germany, was found to be more susceptible to coumatetralyl by a factor of 0.5-0.6 compared to the CD strain. Homozygous and heterozygous animals of a strain of resistant rats from Westphalia were cross-resistant to coumatetralyl and bromadiolone, with a higher resistance factor for bromadiolone than that found in both UK strains. Our results show that the degree of altered susceptibility and resistance varies between strains of wild rat and between resistance foci. Some wild rat strains may be more susceptible than laboratory rat strains. Even in a well-established resistance area, it may be difficult to find infestations with resistance high enough to suspect control problems with bromadiolone, even after decades of use of this compound.

Characterization of two full-sized P elements from Drosophila sturtevanti and Drosophila prosaltans

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

P elements in the saltans group of Drosophila: a new evaluation of their distribution and number of genomic insertion sites

Few are studies on P elements that have addressed the saltans group. These studies had shown that species from the cordata and elliptica subgroups were devoid of any discernible P homologous sequences, while species from the parasaltans, sturtevanti, and saltans subgroups all contain P element sequences. Our analyses showed the presence of one to 15 P element insertion sites in species of the saltans group, including Drosophila neocordata and Drosophila emarginata (cordata and elliptica subgroups, respectively). From these species, only those from the parasaltans, sturtevanti, and saltans subgroups harbor canonical P elements and, only those of the last two subgroups seem to harbor putative full-sized elements. Due to the low similarity of the sequences found in D. neocordata and D. emarginata to those earlier described, we suggest that these sequences might be rudimental P element derivatives that were present in the ancestral of the subgenus Sophophora. (C) 2004 Elsevier B.V. All rights reserved.

Drosophila melanogaster P transposable elements: mechanisms of transposition and regulation

The molecular mechanisms that control P element transposition and determine its tissue specificity remain incompletely understood, although much information has been compiled about this element in the last decade. This review summarizes the currently available information about P element transposition, P-M hybrid dysgenesis and P cytotype features, P element-encoded repressors, and regulation of transposition.

Canonical P elements are transcriptionally active in the saltans group of Drosophila

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.

Transposon display supports transpositional activity of P elements in species of the saltans group of Drosophila

Mobilization of two P element subfamilies (canonical and O-type) from Drosophila sturtevanti and D. saltans was evaluated for copy number and transposition activity using the transposon display (TD) technique. Pairwise distances between strains regarding the insertion polymorphism profile were estimated. Amplification of the P element based on copy number estimates was highly variable among the strains (D. sturtevanti, canonical 20.11, O-type 9.00; D. saltans, canonical 16.4, O-type 12.60 insertions, on average). The larger values obtained by TD compared to our previous data by Southern blotting support the higher sensitivity of TD over Southern analysis for estimating transposable element copy numbers. The higher numbers of the canonical P element and the greater divergence in its distribution within the genome of D. sturtevanti (24.8%) compared to the O-type (16.7%), as well as the greater divergence in the distribution of the canonical P element, between the D. sturtevanti (24.8%) and the D. saltans (18.3%) strains, suggest that the canonical element occupies more sites within the D. sturtevanti genome, most probably due to recent transposition activity. These data corroborate the hypothesis that the O-type is the oldest subfamily of P elements in the saltans group and suggest that the canonical P element is or has been transpositionally active until more recently in D. sturtevanti. © Indian Academy of Sciences.

Gene disruptions using P transposable elements: an integral component of the Drosophila genome project.

Biologists require genetic as well as molecular tools to decipher genomic information and ultimately to understand gene function. The Berkeley Drosophila Genome Project is addressing these needs with a massive gene disruption project that uses individual, genetically engineered P transposable elements to target open reading frames throughout the Drosophila genome. DNA flanking the insertions is sequenced, thereby placing an extensive series of genetic markers on the physical genomic map and associating insertions with specific open reading frames and genes. Insertions from the collection now lie within or near most Drosophila genes, greatly reducing the time required to identify new mutations and analyze gene functions. Information revealed from these studies about P element site specificity is being used to target the remaining open reading frames.