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P Dimitri

Publications and source records attributed to P Dimitri.

At least 19 recordsLinked to original sources
PubMed2006

Drosophila melanogaster as a model for studying protein-encoding genes that are resident in constitutive heterochromatin.

The organization of chromosomes into euchromatin and heterochromatin is one of the most enigmatic aspects of genome evolution. For a long time, heterochromatin was considered to be a genomic wasteland, incompatible with gene expression. However, recent studies--primarily conducted in Drosophila melanogaster--have shown that this peculiar genomic component performs important cellular functions and carries essential genes. New research on the molecular organization, function and evolution of heterochromatin has been facilitated by the sequencing and annotation of heterochromatic DNA. About 450 predicted genes have been identified in the heterochromatin of D. melanogaster, indicating that the number of active genes is higher than had been suggested by genetic analysis. Most of the essential genes are still unknown at the molecular level, and a detailed functional analysis of the predicted genes is difficult owing to the lack of mutant alleles. Far from being a peculiarity of Drosophila, heterochromatic genes have also been found in Saccharomyces cerevisiae, Schizosaccharomyces pombe, Oryza sativa and Arabidopsis thaliana, as well as in humans. The presence of expressed genes in heterochromatin seems paradoxical because they appear to function in an environment that has been considered incompatible with gene expression. In the future, genetic, functional genomic and proteomic analyses will offer powerful approaches with which to explore the functions of heterochromatic genes and to elucidate the mechanisms driving their expression.

Animals↗
PubMed2005

Changing rooms: time for a makeover.

This study explores the concerns expressed by primary school children and their parents about changing arrangements for PE at school. In 39% of schools pupils had expressed anxieties. Are traditional arrangements where children get changed for PE in mixed sex classrooms still appropriate in view of the younger age at which children are now starting puberty?

Anxiety↗
PubMed2005

I element distribution in mitotic heterochromatin of Drosophila melanogaster reactive strains: identification of a specific site which is correlated with the reactivity levels.

The I factor is a Drosophila melanogaster LINE-like element that efficiently transposes in the genetic system of I-R hybrid dysgenesis. It has been suggested that some of the I-related sequences located in the heterochromatin of D. melanogaster are involved in the regulation of I factor activity. In this work we have performed fluorescent in situ hybridization (FISH) mapping of I element sequences in mitotic heterochromatin of nine differentially reactive D. melanogaster strains. The results of our analysis showed that a single hybridization site mapping to region h28 of the distal heterochromatin of the X chromosome is present in three strains with low or intermediate levels of reactivity, while it is undetectable in six highly reactive strains. Together, these observations suggest a negative correlation between I sequences located at h28 and the level of reactivity. To this regard, it is intriguing that flamenco and COM, two loci that regulate the activity of D. melanogaster endogenous retroviruses also map to the distal heterochromatin of the X chromosome. Our data represent the first experimental evidence in favour of a silencing effect exerted by naturally occurring I element sequences located in pericentromeric heterochromatin.

Animals↗
PubMed2005

Transposable elements as artisans of the heterochromatic genome in Drosophila melanogaster.

Over 50 years ago Barbara McClintock discovered that maize contains mobile genetic elements, but her findings were at first considered nothing more than anomalies. Today it is widely recognized that transposable elements have colonized all eukaryotic genomes and represent a major force driving evolution of organisms. Our contribution to this special issue deals with the theme of transposable element-host genome interactions. We bring together published and unpublished work to provide a picture of the contribution of transposable elements to the evolution of the heterochromatic genome in Drosophila melanogaster. In particular, we discuss data on 1) colonization of constitutive heterochromatin by transposable elements, 2) instability of constitutive heterochromatin induced by the I factor, and 3) evolution of constitutive heterochromatin and heterochromatic genes driven by transposable elements. Drawing attention to these topics may have direct implications on important aspects of genome organization and gene expression.

Animals↗
PubMed2001

[Infectious complications in liver transplant in Italy: current status and prospectives].

The impact of infections in orthotopic liver transplantation (OLT) is remarkable. Studies have shown that about 60% of patient may develop at least 1 infectious episode during the first 3 months after transplant. Within the frame of a Finalized Research Project of the Italian Ministry of Health, during the year 2000 a group of investigators belonging to the major Italian Liver Transplant Centers (LTC)--18 out of 20 Centers--met three times in Genoa with the aim of constituting a Research Group aimed at improving our knowledge of infectious complications in liver transplant recipients (PITF = Program of Infections in Liver Transplantation). The group first collected information about anti-infective procedure in LTC. The study shows that no Center is supported by a Intensive Care Unit (ICU) exclusively dedicated to the LTC, although 37% of them have a partially dedicated Unit. Surveillance cultures are routinely performed and are frequently used to address the choice of the antibacterial and antifungal regimes. Selective Bowel Decontamination is also very common. The management of CMV infection is usually performed as indicated in international guidelines.

Anti-Bacterial Agents↗
PubMed1999

A novel simple satellite DNA is colocalized with the Stalker retrotransposon in Drosophila melanogaster heterochromatin.

In the T(1:2)dor(var7) multibreak rearrangement the distal 1A-2B segment of the X chromosome of Drosophila melanogaster is juxtaposed to an inverted portion of the heterochromatin of chromosome 2. Analysis of mitotic chromosomes by a series of banding techniques has permitted us precisely to locate the heterochromatic breakpoint of this translocation in the h42 region of 2R. Cloning and sequencing of the eu-heterochromatic junction revealed that the translocated 1A-2B fragment is joined to (AACAC)n repeats, which represent a previously undescribed satellite DNA in D. melanogaster. These repeated sequences have been estimated to account for about 1 Mb of the D. melanogaster genome. The repeats are located mainly in the Y chromosome and in the heterochromatin of the right arm of chromosome 2 (2Rh), where they are colocalized with the Stalker retrotransposon.

Animals↗
PubMed1999

Revising the selfish DNA hypothesis: new evidence on accumulation of transposable elements in heterochromatin.

The bulk of the eukaryotic genome is composed of families of repetitive sequences that are genetically silent and exhibit various types of instability. Transposable elements (TEs) are particularly common in heterochromatic regions of the genome - a location where TEs might do less damage to their host. Recent advances suggest that the relationship between TEs and heterochromatin might not be quite so straightforward.

Animals↗
PubMed1999

Mobilization of two retroelements, ZAM and Idefix, in a novel unstable line of Drosophila melanogaster.

We describe a novel transposition system in a line of Drosophila melanogaster called RevI in which two retroelements are mobilized. These elements are the retroelement ZAM, recently described in the literature, and a novel element designated Idefix. Like ZAM, Idefix displays the structural features of a vertebrate retrovirus. Its three open reading frames encode predicted products resembling the products of the gag, pol, and env genes of retroviruses. In situ hybridization and Southern analyses performed on the RevI genome revealed the presence of some 20 copies of ZAM and Idefix, whereas ZAM is absent and Idefix is present in only four copies on the chromosomal arms of the original parental line. From RevI, a series of mutations affecting eye coloration has been recovered. The genetic and molecular analyses of these mutations have shown that most of them affected the white locus through three rounds of mutational events. The first mutational event was previously shown to be caused by a ZAM insertion 3 kb upstream of the transcription start site of white. It confers a red-brick phenotype to the orange eye coloration of the parental line. The second event results from the insertion of an Idefix copy 1.7 kb upstream of the transcription start site of the white gene, which modifies the red-brick phenotype to orange. This second mutational event was recovered as a recurrent specific mutation in 11 independent individuals. The third event results from an additional Idefix located 1.7 kb upstream of white that is responsible for the full reversion of the orange phenotype to red-brick. The fact that such mutations due to recurrent appearances of both ZAM and Idefix at the white locus result in such a variety of phenotypes brings to light a new molecular system in which the interference of mobile elements with the correct expression of the host gene can be tested.

Alleles↗
PubMed1999

Phase I-II study of gemcitabine and carboplatin in stage IIIB-IV non-small-cell lung cancer.

PURPOSE: Platinum-based chemotherapy currently represents standard treatment for advanced non-small-cell lung cancer. Gemcitabine is one of the most interesting agents currently in use in advanced non-small-cell lung cancer, and high response rates have been reported when it is administered in combination with cisplatin. The aim of the present study was to evaluate the combination of gemcitabine and carboplatin in a phase I-II study. PATIENTS AND METHODS: Chemotherapy-naive patients with stage IIIB-IV non-small-cell lung cancer received carboplatin at area under the concentration-time curve (AUC) 5 mg/mL/min and gemcitabine at an initial dose of 800 mg/m2, subsequently escalated by 100 mg/m2 per step. Gemcitabine was administered on days 1 and 8 and carboplatin on day 8 of the 28-day cycle. Dose escalation proceeded up to dose-limiting toxicity (DLT), which was defined as grade 4 neutropenia or thrombocytopenia or grade 3 nonhematologic toxicity. RESULTS: Neutropenia was DLT, inasmuch as it occurred in three of five patients receiving gemcitabine 1,200 mg/m2. Nonhematologic toxicities were mild. Gemcitabine 1,100 mg/m2 plus carboplatin AUC 5 was recommended for phase II studies. An objective response was observed in 13 (50%) of 26 patients, including four complete responses (15%) and nine partial responses (35%). Median duration of response was 13 months (range, 3 to 23 months). Median overall survival was 16 months (range, 3 to 26 months). CONCLUSION: The combination of gemcitabine and carboplatin is well tolerated and active. Neutropenia was DLT. The observed activity matches that observable in cisplatin-gemcitabine studies, whereas duration of response and survival are even higher. A phase II trial is under way.

Adult↗
PubMed1997

High genetic instability of heterochromatin after transposition of the LINE-like I factor in Drosophila melanogaster.

In the present work, we have asked whether a group of 13 essential genes mapping to the heterochromatin of Drosophila melanogaster chromosome 2 are mutable following transposition of the I factor during I-R hybrid dysgenesis. We found that the frequency of lethal events mapping to chromosome 2 heterochromatin is surprisingly high, despite the low density of genetic functions identified in this region compared with euchromatin. Cytogenetic and molecular analyses indicated that the recovered mutations correspond either to insertions or to rearrangements. Moreover, chromosomes bearing specific heterochromatic lethal mutations were generated by recombination in the heterochromatin. Together, these data indicate that I factors transpose with high frequency into pericentric regions of chromosome 2 and may play a role in the evolution of constitutive heterochromatin.

Animals↗
PubMed1997

Intragenomic distribution and stability of transposable elements in euchromatin and heterochromatin of Drosophila melanogaster: non-LTR retrotransposon.

The intragenomic location of the elements of the I, G, jockey, F, and Doc transposon families has been studied by the Southern blot analysis, in 12 laboratory Drosophila melanogaster stocks. Elements located in euchromatin, heterochromatin, and on the Y chromosome are identified, and their stability has been assessed by comparing the autoradiographs detected in different stocks and analysis of individual flies. Evidence is shown suggesting that preferential location in euchromatin or heterochromatin and the distribution within heterochromatin are distinctive of transposon families. Elements located in heterochromatin can be unstable. These results are discussed in the context of the relationship between transposable elements and the host genome.

Animals↗
PubMed1997

Intragenomic distribution and stability of transposable elements in euchromatin and heterochromatin of Drosophila melanogaster: elements with inverted repeats Bari 1, hobo, and pogo.

The elements of the Bari 1, hobo, and pogo transposon families that are located in euchromatin, heterochromatin, and on the Y chromosome have been identified, and their stability has been assessed by Southern blot analysis. The fraction of heterochromatic elements appears to be distinctive of all transposon families tested, except for Bari 1. Evidence for instability of heterochromatic elements is described. The analysis of unstable elements in different Drosophila stocks suggests that the host genome contributes to the stability/instability of transposon families.

Animals↗
PubMed1997

Constitutive heterochromatin and transposable elements in Drosophila melanogaster.

Several families of transposable elements (TEs), most of them belonging to the retrotransposon category, are particularly enriched in Drosophila melanogaster constitutive heterochromatin. The enrichment of TE-homologous sequences into heterochromatin is not a peculiar feature of the Drosophila genome, but appears to be widespread among higher eukaryotes. The constitutive heterochromatin of D. melanogaster contains several genetically active domains; this raises the possibility that TE-homologous sequences inserted into functional heterochromatin compartments may be expressed. In this review, I present available data on the genetic and molecular organization of D. melanogaster constitutive heterochromatin and its relationship with transposable elements. The implications of these findings on the possible impact of heterochromatic TEs on the function and evolution of the host genome are also discussed.

Animals↗
PubMed1997

Genomic distribution of the retrovirus-like element ZAM in Drosophila.

The mobile element ZAM, recently identified in Drosophila melanogaster, is similar in structure and coding potential to vertebrate retroviruses. In this paper, we analyze the insertional and structural polymorphism of this element and show that members of this family appear to have a long evolutionary history in the genome of Drosophila. It is present in all the species of the D. melanogaster subgroup and in more distantly related species like D. takahashii, D. ananassae, or D. virilis but in a lower copy number or with a lower homology. Two categories of strains have been previously identified in D. melanogaster: strains with a high copy number of ZAM and strains with a low copy number. Here, we show that ZAM is at least in a low copy number in each tested strain of the species analyzed. The study of ZAM's genomic distribution by FISH mapping analysis to salivary gland polytene chromosomes or on mitotic chromosomes indicates that most of the insertion sites of ZAM elements are associated with the constitutive heterochromatin regardless of the ZAM copy number. In addition, our results suggest that multiple ZAM elements are present at the insertion sites visualized by in situ experiments.

Animals↗
PubMed1996

Accelerated split-course (type B) thoracic radiation therapy plus vinorelbine/carboplatin combination chemotherapy in stage III inoperable non-small cell lung cancer.

43 patients with stage III NSCLC (non-small cell lung cancer) entered a phase II study aimed at evaluating the toxicity and the activity of a combined modality programme including an accelerated split-course schedule (type B) of thoracic radiation therapy and a combination chemotherapy with vinorelbine and carboplatin. An objective response was achieved in 18/42 evaluable patients (5 complete and 13 partial responses), for an overall response rate of 43% (95% confidence interval, 28-58%). Four complete responses had a duration which exceeded 16 months. Treatment was well tolerated; grade III myelotoxicity occurred in only 14% of patients and treatment was delayed in only 2 cases because of grade 3 oesophagitis. Both tolerability and efficacy data suggest that this regimen holds promise for the treatment of patients with stage III NSCLC.

Adult↗
PubMed1996

The heterochromatic rolled gene of Drosophila melanogaster is extensively polytenized and transcriptionally active in the salivary gland chromocenter.

This paper reports a cytogenetic and molecular study of the structural and functional organization of the Drosophila melanogaster chromocenter. The relations between mitotic (constitutive) heterochromatin and alpha- and beta-heterochromatin are not fully understood. In the present work, we have studied the polytenization of the rolled (rl) locus, a 100-kb genomic region that maps to the proximal heterochromatin of chromosome 2 and has been previously thought to contribute to alpha-heterochromatin. We show that rolled undergoes polytenization in salivary gland chromosomes to a degree comparable to that of euchromatic genes, despite its deep heterochromatic location. In contrast, both the Bari-1 sequences and the AAGAC satellite repeats, located respectively the left and right of rl, are severely underrepresented and thus both appear to be alpha-heterochromatic. In addition, we found that rl is transcribed in polytene tissues. Together, the results reported here indicate that functional sequences located within the proximal constitutive heterochromatin can undergo polytenization, contributing to the formation of beta-heterochromatin. The implications of this finding to chromocenter structure are discussed.

Animals↗
PubMed1995

Transposable elements are stable structural components of Drosophila melanogaster heterochromatin.

We determined the distribution of 11 different transposable elements on Drosophila melanogaster mitotic chromosomes by using high-resolution fluorescent in situ hybridization (FISH) coupled with charge-coupled device camera analysis. Nine of these transposable elements (copia, gypsy, mdg-1, blood, Doc, I, F, G, and Bari-1) are preferentially clustered into one or more discrete heterochromatic regions in chromosomes of the Oregon-R laboratory stock. Moreover, FISH analysis of geographically distant strains revealed that the locations of these heterochromatic transposable element clusters are highly conserved. The P and hobo elements, which are likely to have invaded the D. melanogaster genome at the beginning of this century, are absent from Oregon-R heterochromatin but clearly exhibit heterochromatic clusters in certain natural populations. Together these data indicate that transposable elements are major structural components of Drosophila heterochromatin, and they change the current views on the role of transposable elements in host genome evolution.

Animals↗