Biomedical subjects

S Siljak-Yakovlev

Publications and source records attributed to S Siljak-Yakovlev.

11 recordsLinked to original sources

PubMed2005

Evolution of the chromosomal location of rDNA genes in two Drosophila species subgroups: ananassae and melanogaster.

The evolution of the chromosomal location of ribosomal RNA gene clusters and the organization of heterochromatin in the Drosophila melanogaster group were investigated using fluorescence in situ hybridization and DAPI staining to mitotic chromosomes. The investigation of 18 species (11 of which were being examined for the first time) belonging to the melanogaster and ananassae subgroups suggests that the ancestral configuration consists of one nucleolus organizer (NOR) on each sex chromosome. This pattern, which is conserved throughout the melanogaster subgroup, except in D. simulans and D. sechellia, was observed only in the ercepeae complex within the ananassae subgroup. Both sex-linked NORs must have been lost in the lineage leading to D. varians and in the ananassae and bipectinata complexes, whereas new sites, characterized by intra-species variation in hybridization signal size, appeared on the fourth chromosome related to heterochromatic rearrangements. Nucleolar material is thought to be required for sex chromosome pairing and disjunction in a variety of organisms including Drosophila. Thus, either remnant sequences, possibly intergenic spacer repeats, are still present in the sex chromosomes which have lost their NORs (as observed in D. simulans and D. sechellia), or an alternative mechanism has evolved.

Animals↗

PubMed2005

Nuclear DNA content and chromosome number in some diploid and tetraploid Centaurea (Asteraceae: Cardueae) from the Dalmatia region.

Given the paucity of information about genome size in the genus Centaurea, nuclear DNA content of 15 Centaurea taxa, belonging to four subgenera and six different sections, has been investigated for the first time. The sample concerns 21 populations from the Dalmatia region of Croatia. The 2C DNA content and GC percentage were assessed by flow cytometry and chromosome number was determined using standard methods. Genome size of studied Centaurea ranged from 2C=1.67 to 3.72 pg. These results were in accordance with chromosome number and especially with ploidy level that varies throughout this group; 2C DNA values ranged from 1.67 to 3.43 pg for diploid, and from 3.19 to 3.72 for polyploid taxa. No significant intraspecific variations of DNA amount were found between two subspecies of C. visiani and C. ragusina, nor between two varieties of C. gloriosa. However, some populations of C. glaberrima and C. cuspidata showed a significant difference in DNA amount. Three different basic chromosome numbers were observed in studied species (x=9, 10, and 11). The most frequent basic number was x=9. C. rupestris, C. ragusina ssp. ragusina, and C. r. ssp. lungensis possessed x=10 and C. tuberosa x=11. The species with a basic chromosome number of x=9 had a small genome size and the smallest chromosomes (on average 0.09 to 0.12 pg/chromosome) but frequently present polyploidy. Centaurea ragusina ssp. ragusina and C. r. ssp. lungensis had a mean base composition 41.3% GC.

Centaurea↗

PubMed2003

Genome size and base composition of five Pinus species from the Balkan region.

The 2C DNA content and base composition of five Pinus (2 n=24) species and two Pinus subspecies from the Balkan region have been estimated by flow cytometry. P. heldreichii (five populations) and P. peuce (one population) were assessed for the first time, as also were subspecies of P. nigra (three populations-two of subspecies nigra and one of subspecies dalmatica) along with P. sylvestris, and P. mugo from the same region. The 2C DNA values of these Pinus ranged from 42.5 pg to 54.9 pg (41.7-53.8 x 10(9)bp), and the base composition was quite stable (about 39.5% GC). Significant differences were observed between two subspecies of P. nigra and even between two populations of subsp. nigra. The two other species (P. sylvestris and P. mugo) had 2C values of 42.5 pg and 42.8 pg, respectively, while that of P. peuce was 54.9 pg. These genome sizes are in accordance with published values except for P. sylvestris, which was 20% below estimates made by other authors.

Base Composition↗

PubMed2003

Postmeiotic cytokinesis and pollen aperture number determination in eudicots: effect of the cleavage wall number.

In eudicot postmeiotic tetrads, apertures are usually joined in pairs in highly conserved areas. These appear to be located at the last points of contact persisting at the end of cytokinesis between the cytoplasm of the future microspores. In order to investigate the relationship between cytokinesis and aperture formation, aperture distribution within postmeiotic tetrads and the progression of meiosis were studied in Nicotiana tabacum cv. Ambalema. This variety (inbred line) produces about 85% tricolporate pollen and 15% tetracolporate pollen grains. In addition, about 7% of tetrads are composed of four equal-sized microspores and a supernumerary pseudomicrospore of small size and an equal proportion of tetrads exhibit unpaired apertures (these apertures are not joined in pairs within tetrads). Observation of cytokinesis indicates that both unpaired apertures and pseudomicrospores could result from the persistence of late communications between microsporocytes. Observations of tetrads indicate that an increase in the number of elements that are separated during cytokinesis is correlated with an increase in microspore aperture number. All data converge to support the hypothesis that aperture site determination is partly controlled by the number of walls formed to separate the different elements of the tetrad.

Cell Division↗

PubMed2001

Source of resistance against Ralstonia solanacearum in fertile somatic hybrids of eggplant (Solanum melongena L.) with Solanum aethiopicum L.

Solanum aethiopicum is reported to carry resistance to bacterial wilt disease caused by Ralstonia solanacearum, which is one of the most important diseases of eggplant (Solanum melongena). These two species can sexually be crossed but the fertility of their progeny is very low. In order to transfer the resistance and improve the fertility, somatic hybrids between S. melongena cv. Dourga and two groups of S. aethiopicum were produced by electrical fusion of mesophyll protoplasts. Thirty hybrid plants were regenerated. When transferred to the greenhouse and transplanted in the field, they were vigorous and showed intermediate morphological traits. Their ploidy level was determined by DNA analysis through flow cytometry, and their hybrid nature was confirmed by examining isozymes and RAPDs patterns. Chloroplast DNA microsatellite analysis revealed that 18 hybrids had the chloroplasts of the eggplant and 12 those of the wild species. The parents and 16 hybrids were evaluated in the field for their fertility and resistance to bacterial wilt using a race 1, biovar 3 strain of R. solanacearum. All hybrids were fertile and set fruit with viable seeds. Their yield was either intermediate or as high as that of the cultivated eggplant. Both groups of S. aethiopicum were found tolerant to R. solanacearum, as about 50% of plants wilted after 8 weeks. The cultivated eggplant was susceptible with 100% of wilted plants 2 weeks after inoculation. All somatic hybrids tested were as tolerant as the wild species, except six hybrids showing a better level of resistance.

Journal Article↗

PubMed2001

Representational difference analysis reveals genomic differences between Q. robur and Q. suber: implications for the study of genome evolution in the genus Quercus.

Very similar genome sizes, similar karyotypes and heterochromatin organisation, and identical number/position of ribosomal loci characterise the common oak (Q. robur) and the cork oak (Q. suber), two distantly related oak species. Representational Difference Analysis (RDA) was used to subtract the genome of Q. suber from the genome of Q. robur in order to search for genome differentiation. A library of 400 clones (bearing RDA fragments) representing genome differences between the two species was obtained. Seven Q. robur-specific DNA sequences were analysed with respect to their molecular and chromosome organisation. All belong to the dispersed repetitive component of the genome, as revealed by Southern hybridisation and in situ hybridisation. They are present in the Q. robur genome in between 100 and 700 copies, and are distributed along the length of almost all chromosomes. A search for homologies between RDA fragments and sequences in Genbank revealed similarities of all RDA fragments with known retrotransposons. The RDA fragments were also tested for their presence/absence in the genomes of six additional oak species belonging to different phylogenetic groups, in order to examine the evolutionary dynamics of these DNA sequences.

Base Sequence↗

PubMed1999

Evolutionary DNA variation in the genus hypochaeris

The genome size and the base composition (GC%) of eight Hypochaeris species were determined by flow cytometry in order to establish the pattern of nuclear DNA variation within the genus. The species analysed showed an almost fivefold range of variation from 1.68 pg in H. cretensis to 8.10 pg in H. uniflora. This variation in DNA content is greater between taxonomic sections of Hypochaeris species than within a section. There was no correlation between 2C DNA content and GC% indicating that neither the GC fraction nor the AT fraction were preferentially associated with variation in genome size. Because there is little heterochromatin, these results show that it is interspersed repeated sequences that are most probably implicated in this variation. From phylogenetic analysis, it is likely that genome size has evolved by loss of DNA content in some lineages and by gain in one lineage from an ancestral genome which was probably similar to genomes of intermediate size in Hypochaeris.

Journal Article↗

PubMed1998

Molecular phylogeny of the genus Hypochaeris using internal transcribed spacers of nuclear rDNA: inference for chromosomal evolution.

Sequences of the internal transcribed spacers (ITSs) of 18S-26S nuclear ribosomal DNA were used to resolve phylogenetic relationships and chromosomal evolution among 14 species of the genus Hypochaeris (Asteraceae). Parsimony analysis was performed for phylogenetic reconstruction, and sequence divergence between species was estimated. Pairwise sequence divergence within Hypochaeris genus ranged from 0% to 25.68% in ITS1 and from 0% to 17.08% in ITS2. A highly resolved strict-consensus tree was obtained that showed the phylogenetically useful information of ITS sequences within the genus Hypochaeris. Four clades could be well distinguished, one of them formed by the single species H. robertia, which appeared to be the most related to the ancestral species of the genus. The results agree with taxonomic classification based on morphological data, and the tree obtained, when indels are coded as missing data, aggregates the species having the same chromosome number, except in one clade. According to the ITS phylogenetic tree, the chromosomal evolution within the genus Hypochaeris conflicts with the previous hypothesis and suggests that karyotype evolution in Hypochaeris was accompanied with both decreasing and increasing dysploidy, probably with several chromosomal rearrangements, and from an ancestral basic chromosome number of 4 or 5.

Asteraceae↗

PubMed1995

Genome size, fluorochrome banding, and karyotype evolution in some Hypochoeris species.

Four South American and two European species of Hypochoeris (Asteraceae) were studied using fluorochrome banding, and genome size was determined by flow cytometry, in order to obtain information about microevolution in this genus and about its primary origin. Fluorochrome banding patterns showed GC-rich repeated sequences, particularly around the nucleolar organizer regions. Few differences appeared among the South American species. Nevertheless, determination of nuclear DNA content and base composition revealed significant differences among these species. The phylogenetic position of Hypochoeris robertia, which has the smallest DNA content, is discussed with regard to chromosome evolution in this genus.

Biological Evolution↗

PubMed1993

Heterochromatin study demonstrating the non-linearity of fluorometry useful for calculating genomic base composition.

A novel procedure for calculating base-pair frequencies in whole genomes is reported. This has been developed during a study of the role of heterochromatin in microevolution. Closely related species of the Crepis praemorsa complex have similar karyotypes but for their heterochromatin. The changes in relative AT frequency between species have been attributed to heterochromatin sequences by in situ banding of chromosomes with two base-specific fluorochromes. The absolute genome size of species, measured by cytofluorometry, correlated positively with increased karyotypic heterochromatin, as did the proportion of AT bases in the DNA. However, the determination of base content has called for a curvilinear interpretation of data obtained with two base-specific fluorochromes (bisbenzimide Hoechst 33342 and mithramycin), in contrast to the commonly assumed but erroneous direct relationship between fluorescence intensity and base content. Essentially, the fluorochromes' requirements for a sequence of certain base-pairs lead to the notion of Coefficients of Overspecificity: the result is a simple formula for calculating the AT proportion in a genome relative to a reference species from cytometric data, taking account of ligand binding statistics. These statistics and probabilities of oligonucleotide binding are essentially the same.

Adenine↗

PubMedDate not supplied

Molecular cytogenetics of Xeranthemum L. and related genera (Asteraceae, Cardueae).

Seven representatives of the genera Amphoricarpus, Chardinia, Siebera, and Xeranthemum, all of them closely related as demonstraded by molecular phylogeny, have been studied from a cytogenetic perspective. Morphometrical karyotype parameters were calculated and idiograms obtained. Fluorochrome banding was performed with chromomycin A (3) to identify GC-rich regions in the chromosomes. Fluorescence in situ hybridization allowed us to locate the sites of 18S-5.8S-26S and 5S rDNA. Silver nitrate staining was used to count the number of nucleoli and to detect the active nucleolar organizing regions. Systematic and evolutionary issues are addressed in the light of these data.

Asteraceae↗