Paolo Barsanti

Individual variation of the nucleolus organizer regions in Allium cepa and A. sativum

Intraspecific variability of rDNA content in two cultivars of Allium cepa and in a strain of Allium sativum (U type) was studied by filter hybridization of 3H-rRNA with DNA extracted from roots of individual bulbs. The range of variation in% hybrid values was 2-fold (0.052% to 0.106%) and 2.5-fold (0.049% to 0.124%) in the two Allium cepa cultivars, but it was much smaller (0.048% to 0.061%) in the Allium sativum strain. — In both Allium cepa cultivars studied plants were observed carrying two, three or four nucleolus organizers per cell; cytological polymorphism of the nucleolus organizer regions was demonstrated by Giemsa C-banding. The number of ribosomal cistrons per genome of the bulb does not seem to be strictly dependent upon the number of nucleolus organizers per cell, and no relationship was detected between Giemsa banding pattern of nucleolar chromosomes and rDNA content of the bulb.

Comparison of the oxidative phosphorylation (OXPHOS) nuclear genes in the genomes of Drosophila melanogaster, Drosophila pseudoobscura and Anopheles gambiae

BackgroundIn eukaryotic cells, oxidative phosphorylation (OXPHOS) uses the products of both nuclear and mitochondrial genes to generate cellular ATP. Interspecies comparative analysis of these genes, which appear to be under strong functional constraints, may shed light on the evolutionary mechanisms that act on a set of genes correlated by function and subcellular localization of their products.ResultsWe have identified and annotated the Drosophila melanogaster, D. pseudoobscura and Anopheles gambiae orthologs of 78 nuclear genes encoding mitochondrial proteins involved in oxidative phosphorylation by a comparative analysis of their genomic sequences and organization. We have also identified 47 genes in these three dipteran species each of which shares significant sequence homology with one of the above-mentioned OXPHOS orthologs, and which are likely to have originated by duplication during evolution. Gene structure and intron length are essentially conserved in the three species, although gain or loss of introns is common in A. gambiae. In most tissues of D. melanogaster and A. gambiae the expression level of the duplicate gene is much lower than that of the original gene, and in D. melanogaster at least, its expression is almost always strongly testis-biased, in contrast to the soma-biased expression of the parent gene.ConclusionsQuickly achieving an expression pattern different from the parent genes may be required for new OXPHOS gene duplicates to be maintained in the genome. This may be a general evolutionary mechanism for originating phenotypic changes that could lead to species differentiation.

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 nuclear OXPHOS genes in insecta: a common evolutionary origin, a common cis-regulatory motif, a common destiny for gene duplicates

BackgroundWhen orthologous sequences from species distributed throughout an optimal range of divergence times are available, comparative genomics is a powerful tool to address problems such as the identification of the forces that shape gene structure during evolution, although the functional constraints involved may vary in different genes and lineages.ResultsWe identified and annotated in the MitoComp2 dataset the orthologs of 68 nuclear genes controlling oxidative phosphorylation in 11 Drosophilidae species and in five non-Drosophilidae insects, and compared them with each other and with their counterparts in three vertebrates (Fugu rubripes, Danio rerio and Homo sapiens) and in the cnidarian Nematostella vectensis, taking into account conservation of gene structure and regulatory motifs, and preservation of gene paralogs in the genome. Comparative analysis indicates that the ancestral insect OXPHOS genes were intron rich and that extensive intron loss and lineage-specific intron gain occurred during evolution. Comparison with vertebrates and cnidarians also shows that many OXPHOS gene introns predate the cnidarian/Bilateria evolutionary split. The nuclear respiratory gene element (NRG) has played a key role in the evolution of the insect OXPHOS genes; it is constantly conserved in the OXPHOS orthologs of all the insect species examined, while their duplicates either completely lack the element or possess only relics of the motif.ConclusionOur observations reinforce the notion that the common ancestor of most animal phyla had intron-rich gene, and suggest that changes in the pattern of expression of the gene facilitate the fixation of duplications in the genome and the development of novel genetic functions.

dtctex-1, the Drosophila melanogaster homolog of a putative murine t-complex distorter encoding a dynein light chain, is required for production of functional sperm.

Abstract. Tctex-1 is a light chain of the cytoplasmic and flagellar dyneins and a candidate for one of the distorter products that cause transmission ratio distortion in mice. We report the identification, characterization, and a preliminary mutational analysis of the function of the Drosophila melanogaster dtctex-1 gene, the putative ortholog of the mammalian tctex-1 gene family. Four P-transposon insertions which disrupt the 5′ untranslated region of dtctex-1 are viable in homozygous form but cause male sterility due to the production of non-motile sperm. In males homozygous for dtctex-1 mutant alleles the dtctex-1 transcript is undetectable, while in homozygous females transcripts of lower molecular weight are present. By secondary mobilization of P-element insertions several revertants and new mutant alleles carrying deletions in the 5′ UTR region of the gene were produced and characterized by PCR and by Northern analysis.

Genetic, molecular and developmental analysis of the glutamine synthetase isozymes of Drosophila melanogaster.

The glutamine synthetase isozymes ofDrosophila melanogaster offer an attractive model for the study of the molecular genetics and evolution of a small gene family encoding enzymatic isoforms that evolved to assume a variety of specific and sometimes essential biological functions. InDrosophila melanogaster two GS. isozymes have been described which exhibit different cellular localisation and are coded by a two-member gene family. The mitochondrial GS structural gene resides at the 21B region of the second chromosome, the structural gene for the cytosolic isoform at the 10B region of the X chromosome. cDNA clones corresponding to the two genes have been isolated and sequenced. Evolutionary analysis data are in accord with the hypothesis that the twoDrosophila glutamine synthetase genes are derived from a duplication event that occurred near the time of divergence between Insecta and Vertebrata. Both isoforms catalyse all reactions catalysed by other glutamine synthetases, but the different kinetic parameters and the different cellular compartmentalisation suggest strong functional specialisation. In fact, mutations of the mitochondrial GS gene produce embryo-lethal female sterility, defining a function of the gene product essential for the early stages of embryonic development. Preliminary results show strikingly distinct spatial and temporal patterns of expression of the two isoforms at later stages of development.

A genetic analysis of the porin gene encoding a voltage-dependent anion channel protein in Drosophila melanogaster

Abstract. The voltage-dependent anion channel (VDAC, also known as porin) is an abundant protein in the outer mitochondrial membrane that forms transmembrane channels permeable to solutes. While in mammals at least three different porin genes have been found, only one VDAC-encoding gene, porin, has been described so far in Drosophila melanogaster. It produces transcripts with alternative

Identification of nuclear genes encoding mitochondrial proteins: isolation of a collection of D. melanogaster cDNAs homologous to sequences in the Human Gene Index database

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