Carmen Di Franco

Accumulation of Transposable Elements in the Heterochromatin and on the Y Chromosome of Drosophila simulans and Drosophila melanogaster

Abstract. The elements of the transposon families G, copia, mdg 1, 412, and gypsy that are located in the heterochromatin and on the Y chromosome have been identified by the Southern blotting technique in Drosophila simulans and D. melanogaster populations. Within species, the abundance of such elements differs between transposon families. Between species, the abundance in the heterochromatin and on the Y chromosome of the elements of the same family can differ greatly suggesting that differences within a species are unrelated to structural features of elements. By shedding some new light on the mechanism of accumulation of transposable elements in the heterochromatin, these data appear relevant to the understanding of the long-term interaction between transposable elements and the host genome.

Transposition of copia-like nomadic elements can be induced by heat shock

SummaryFour males of an isogenic gt waDrosophila line were heat shocked and then crossed with isogenic untreated females. The genomic distributions of the elements of five copia-like families were analyzed in the four F1 flies by the Southern technique and compared with those in the untreated isogenic line. The pattern heterogeneity observed in the F1 samples shows that extensive rearrangements can be induced by heat shock.

The Tumor Marker Human Placental Protein 11 Is an Endoribonuclease

Human PP11 (placental protein 11) was previously described as a serine protease specifically expressed in the syncytiotrophoblast and in numerous tumor tissues. Several PP11-like proteins were annotated in distantly related organisms, such as worms and mammals, suggesting their involvement in evolutionarily conserved processes. Based on sequence similarity, human PP11 was included in a protein family whose characterized members are XendoU, a Xenopus laevis endoribonuclease involved in small nucleolar RNA processing, and Nsp15, an endoribonuclease essential for coronavirus replication. Here we show that the bacterially expressed human PP11 displays RNA binding capability and cleaves single stranded RNA in a Mn2+-dependent manner at uridylates, to produce molecules with 2′,3′-cyclic phosphate ends. These features, together with structural and mutagenesis analyses, which identified the potential active site residues, reveal striking parallels to the amphibian XendoU and assign a ribonuclease function to PP11. This newly discovered enzymatic activity places PP11-like proteins in a completely new perspective.

Genomic distribution of copia-like transposable elements in somatic tissues and during development of Drosophila melanogaster

The genomic distribution of elements of the copia, 412, B 104, mdg 1, mdg 4 and 1731 transposon families was compared by the Southern technique in DNA preparations extracted from brains, salivary glands and adult flies of two related Drosophila lines. The copia, 412 and mdg 1 sequences were also probed in DNA from sperm, embryos, and 1st and 2nd instar larvae. The homogeneity of the patterns observed shows that somatic transposition is unlikely to occur frequently. A correlation between mobility and the euchromatic or heterochromatic location of transposable elements is discussed. In addition, an explanation of the variable band intensities of transposable elements in Southern autoradiographs is proposed.

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.

Potentially active copies of the gypsy retroelement are confined to the Y chromosome of some strains of Drosophila melanogaster possibly as the result of the female-specific effect of the flamenco gene.

Gypsy is an endogenous retrovirus present in the genome of Drosophila melanogaster. This element is mobilized only in the progeny of females which contain active gypsy elements and which are homozygous for permissive alleles of a host gene called flamenco (flam). Some data strongly suggest that gypsy elements bearing a diagnostic HindIII site in the central region of the retrovirus body represent a subfamily that appears to be much more active than elements devoid of this site. We have taken advantage of this structural difference to assess by the Southern blotting technique the genomic distribution of active gypsy elements. In some of the laboratory Drosophila stocks tested, active gypsy elements were found to be restricted to the Y chromosome. Further analyses of 14 strains tested for the permissive vs. restrictive status of their flamenco alleles suggest that the presence of permissive alleles of flam in a stock tends to be associated with the confinement of active gypsy elements to the Y chromosome. This might be the result of the female-specific effect of flamenco on gypsy activity.

Intragenomic Distribution and Stability of Transposable Elements in Euchromatin and Heterochromatin of Drosophila melanogaster: Elements with Inverted Repeats Bari 1, hobo, and pogo

Abstract. 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.

Evidence for a host role in regulating the activity of transposable elements in Drosophila melanogaster: the case of the persistent instability of Bari 1 elements in Charolles stock

In most reports in which the activity of numerous Drosophila transposon families has been studied, only a subset of the families tested appears mobile. A comparison of these data shows that there are no transposons inherently more unstable than others and suggests that host factors regulate the activity of transposable elements. Consistent with this conclusion are the properties of Bari 1 elements, which are the only ones of the 14 families tested to be unstable in Charolles stock. Instability is persistent over 53 generations and appears to affect recurrent insertion sites.

Localization of new peptidoglycan at poles in Bacillus mycoides, a member of the Bacillus cereus group

Bacillus mycoides is a sporogenic Gram-positive soil bacillus of the B. cereus group. This bacillus, which forms hyphal colonies, is composed of cells connected in filaments that make up bundles and turn clock- or counterclockwise depending on the strain. A thick peptidoglycan wall gives the rod cells of these bacilli strength and shape. One approach used to study peptidoglycan neoformation in Gram positives exploits the binding properties of antibiotics such as vancomycin and ramoplanin to nascent peptidoglycan, whose localization in the cell is monitored by means of a fluorescent tag. When we treated B. mycoides strains with BODIPY-vancomycin, we found the expected accumulation of fluorescence at the midcell septa and localization along the cell sidewall in small foci distributed quite uniformly. Intense fluorescence was also observed at the poles of many cells, more clearly visible at the outer edges of the cell chains. The unusual abundance of peptidoglycan intermediates at the cell poles after cell separation suggests that the construction process of this structure is different from that of B. subtilis, in which the free poles are rarely reactive to vancomycin.

Transcriptional analysis of ftsZ within the dcw cluster in Bacillus mycoides

BackgroundIn Bacillus mycoides, as well as in other members of the B. cereus group, the tubulin-like protein of the division septum FtsZ is encoded by the distal gene of the cluster division and cell wall (dcw). Along the cluster the genes coding for structural proteins of the division apparatus are intermingled with those coding for enzymes of peptidoglycan biosynthesis, raising the possibility that genes with this different function might be coexpressed. Transcription of ftsZ in two model bacteria had been reported to differ: in B. subtilis, the ftsZ gene was found transcribed as a bigenic mRNA in the AZ operon; in E. coli, the transcripts of ftsZ were monogenic, expressed by specific promoters. Here we analyzed the size and the initiation sites of RNAs transcribed from ftsZ and from other cluster genes in two B. mycoides strains, DX and SIN, characterized by colonies of different chirality and density, to explore the correlation of the different morphotypes with transcription of the dcw genes.ResultsIn both strains, during vegetative growth, the ftsZ-specific RNAs were composed mainly of ftsZ, ftsA-ftsZ and ftsQ-ftsA-ftsZ transcripts. A low number of RNA molecules included the sequences of the upstream murG and murB genes, which are involved in peptidoglycan synthesis. No cotranscription was detected between ftsZ and the downstream genes of the SpoIIG cluster. The monogenic ftsZ RNA was found in both strains, with the main initiation site located inside the ftsA coding sequence. To confirm the promoter property of the site, a B. mycoides construct carrying the ftsA region in front of the shortened ftsZ gene was inserted into the AmyE locus of B. subtilis 168. The promoter site in the ftsA region was recognized in the heterologous cellular context and expressed as in B. mycoides.ConclusionsThe DX and SIN strains of B. mycoides display very similar RNA transcription specificity. The ftsZ messenger RNA can be found either as an independent transcript or expressed together with ftsA and ftsQ and, in low amounts, with genes that are specific to peptidoglycan biosynthesis.