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PubMed2006

Multiple rounds of speciation associated with reciprocal gene loss in polyploid yeasts.

A whole-genome duplication occurred in a shared ancestor of the yeast species Saccharomyces cerevisiae, Saccharomyces castellii and Candida glabrata. Here we trace the subsequent losses of duplicated genes, and show that the pattern of loss differs among the three species at 20% of all loci. For example, several transcription factor genes, including STE12, TEC1, TUP1 and MCM1, are single-copy in S. cerevisiae but are retained in duplicate in S. castellii and C. glabrata. At many loci, different species have lost different members of a duplicated gene pair, so that 4-7% of single-copy genes compared between any two species are not orthologues. This pattern of gene loss provides strong evidence for speciation through a version of the Bateson-Dobzhansky-Muller mechanism, in which the loss of alternative copies of duplicated genes leads to reproductive isolation. We show that the lineages leading to the three species diverged shortly after the whole-genome duplication, during a period of precipitous gene loss. The set of loci at which single-copy paralogues are retained is biased towards genes involved in ribosome biogenesis and genes that evolve slowly, consistent with the hypothesis that reciprocal gene loss is more likely to occur between duplicated genes that are functionally indistinguishable. We propose a simple, unified model in which a single mechanism--passive gene loss-enabled whole--genome duplication and led to the rapid emergence of new yeast species.

Alleles↗
PubMed2004

Microsatellite DNA marker inheritance indicates preferential pairing between two highly homologous genomes in polyploid and hemisexual dog-roses, Rosa L. Sect. Caninae DC.

According to previous cytological evidence, the hemisexual dog-rose species, Rosa sect. Caninae, transmit only seven chromosomes (derived from seven bivalents) through their pollen grains, whereas egg cells contain 21, 28 or 35 chromosomes (derived from seven bivalents and 14, 21 or 28 univalents) depending on ploidy level. Two sets of reciprocal pairwise interspecific crosses involving the pentaploid species pair R. dumalis and R. rubiginosa, and the pentaploid/tetraploid species pair R. sherardii and R. villosa, were analysed for 13 and 12 microsatellite DNA loci, respectively. Single loci were represented by a maximum of three simultaneously occurring alleles in R. villosa, and four alleles in the other three parental plants. In the experimentally derived offspring, the theoretical maximum of five alleles was found for only one locus in the pentaploid progenies. Microsatellite DNA allele composition was identical with that of the maternal parent in 10 offspring plants, which were probably derived through apomixis. Almost all microsatellite DNA alleles were shared with the maternal parent also in the remaining offspring, but 1-4 alleles shared only with the paternal parent, indicating sexual seed formation. Analysis of quantitative peak differences allowed a tentative estimation of allelic configuration in the individual plants, and suggested that bivalent formation preferentially takes place between chromosomes that consistently share the same microsatellite alleles and therefore appear to be highly homologous. Moreover, alleles that were shared between the species in each cross combination comparatively often appear to reside on the bivalent-forming chromosomes, whereas species-specific alleles instead occur comparatively often on the univalent-forming chromosomes and are therefore inherited through the maternal parent only. Recombination then takes place between very similar genomes also in interspecific crosses, resulting in a reproduction system that is essentially a mixture between apomixis and selfing.

Alleles↗
PubMed2000

Transglobal comparisons of nuclear and mitochondrial genetic structure in a marine polyploid clam (Lasaea, Lasaeidae).

Existing genetic studies have proposed that the intertidal clam, Lasaea, is one of a few animal groups with asexual lineages that has persisted for an evolutionarily significant time. This proposal is based on the exceptional mitochondrial genetic divergence between studied sexual and asexual lineages. Nevertheless, a conclusion of long-lived asexuality awaits a more comprehensive sampling of the collective global range of this taxon. We assessed the breeding system and phylogeography of geographically divergent Lasaea populations using nuclear and mtDNA genetic markers. The allozyme genetic structure of five populations (from Japan, New Zealand, South Africa, Florida and Bermuda) showed marked deviation from expected random mating patterns (within and among loci), frequent fixed heterozygosity, and reduced genotypic diversity. This pattern and the finding of multiple asymmetric allozymic heterozygotes, indicated a clonal structure consistent with allopolyploid origins for each population. Spatial analysis of mtDNA and allozyme markers revealed strong geographical structure and yielded no cosmopolitan clonal lineages. Australian sexual species formed sister taxa to a minority of the clonal lineages, but pronounced mitochondrial genetic divergence levels and developmental differences precluded their identification as convincing parental species to any of the clones. A majority of asexual lineages may have originated in areas where no sexual congeners are presently known. The observed nuclear and mtDNA genetic structure is consistent with Lasaea clonal diversity being enriched by local mutational derivatives but infrequent recombination cannot be ruled out.

Animals↗
PubMed2001

Allozyme segregation and inter-cytotype reproductive barriers in the polyploid complex Centaurea jacea.

In eastern Belgium, diploid and tetraploid knapweeds (Centaurea jacea L. s. l.) show a parapatric distribution with a contact zone. To compare the success of inter- and intra-cytotype crosses, and to investigate the pattern of allozyme segregation, controlled crosses involving plants from this contact zone were performed. Polysomic inheritance at two loci was observed in tetraploids, suggesting an autopolyploid origin. Two crosses allowed the detection of double reduction events in tetraploids at one locus, but no such event was detected among the 217 progenies. Null alleles were detected in tetraploids at two loci. Both cytotypes were highly self-incompatible. Inter-cytotype crosses were much less successful than intra-cytotype crosses in terms of seed set (five-fold reduction) and germination rates (three-fold reduction), suggesting a 'triploid block' effect. Progenies from inter-cytotype crosses most often had the maternal cytotype and resulted from selfing or pollen contamination. However, six triploids were detected. The significance of these results for the understanding of the geographical distribution of the cytotypes and inter-cytotype gene flow is discussed.

Alleles↗
PubMed1988

Polyploid abnormalities in day 3 and day 5 merino sheep embryos.

The chromosome complement was assessed in Merino sheep embryos collected at 3 and 5 days after the onset of oestrus. Donor ewe treatments were: untreated, or immunized against androstenedione (day 3); and untreated, or treated with follicle-stimulating hormone (FSH), or treated with FSH plus immunization against androstenedione (day 5). No significant differences in the frequency of chromosomally abnormal embryos between treatment groups within each age group were observed, so the data have been combined. Euploid abnormalities were observed in 10.8% of the day-3 embryos (4/37), with the abnormalities being one 1n, one 3n and two 5n. Embryos with euploidy (10%) were also observed at day 5, with three 1n/2n mosaics and a 3n embryo present in a sample of 40. These data suggest that chromosomally aberrant embryos are not lost before day 5 of development.

Androstenedione↗
PubMed1987

Role of cytoplasm-specific introgression in the evolution of the polyploid wheats.

Studies of N-banded mitotic and meiotic karyotypes of Triticum turgidum L. (2n = 28; AABB) and Triticum timopheevii Zhuk. (2n = 28; AAGG) and hybrids between them, along with observations of meiotic pairing between telocentrics of the AB-genome chromosomes and their respective homologues and homeologues in T. timopheevii, showed that chromosome 4 (m4) of Triticum monococcum L. is present (as 4A(t)) in T. timopheevii but is lacking in T. turgidum. Neither 4A nor 4B pairs with 4A(t), but 4A pairs with 4G and, for this reason and because of its banding pattern, must be considered a B-genome chromosome. T. timopheevii chromosomes 4A(t) and 3A(t) are involved in a reciprocal translocation, and 2A(t), 1G, 2G, and 5G are also involved in translocations. Chromosome arm 4BL occasionally pairs with 7G. The satellites are on the short arms of chromosomes 6A(t) and 6G of T. timopheevii and 1B and 6B of T. turgidum. It is suggested that (i) T. timopheevii orginated as an allotetraploid of Aegilops speltoides Tausch/T. monococcum and (ii) T. turgidum was derived from T. timopheevii by introgressive hybridization with an unknown diploid species, which contributed its distinctive cytoplasm, chromosome 4B or a substantial portion of it, and additional chromosome segments. Rapid fixation of 4B in T. turgidum was ensured by cytoplasm-specific transmission.

Journal Article↗
PubMed2003

Vascular smooth muscle polyploidization as a biomarker for aging and its impact on differential gene expression.

Polyploidy is characterized by a greater than diploid content of DNA in a cell. Previous measurements of ploidy level in different organs of humans and rodents, including the aorta, indicated an increase in old versus young. We hypothesized that aortic vascular smooth muscle polyploidy is a biomarker for aging and that the augmented DNA dosage affects selective gene-specific transcript expression. Our results demonstrate that tetraploidy increases exponentially over the life span of the animal, serving as an indicator of age. Approximately 60% of the vascular smooth muscle cells in the thoracic aorta of 36-month-old Brown Norway rats are tetraploid compared with 8% in their 3-month-old counterparts. Microarray analysis and reverse transcriptase-PCR was performed with mRNA isolated from sorted diploid (2N) and tetraploid (4N) vascular smooth muscle cells from old rats to identify differentially expressed transcripts. For the majority of detectable transcripts, an increase in DNA content led to a proportional increase in mRNA. A select group of transcripts, however, were reduced in tetraploid compared with diploid cells. These mRNAs correspond to guanine deaminase, to the matrix proteins rat glypican 3 (OCI-5) and decorin, as well as to the inflammation-associated transcripts, insulin-like growth factor-binding protein 6, macrophage inflammatory protein 2 precursor, macrophage galactose N-acetylgalactoseamine-specific lectin, and complement component C4. Our study is the first to describe aortic ploidy level as a biomarker for aging and to indicate that changes associated with increased DNA content per cell may selectively suppress the expression of specific genes.

Animals↗
PubMed1984

An analysis of the platelet and polyploid megakaryocyte response to acute thrombocytopenia and its biological implications.

Thrombocytopenia was induced in rabbit by a single injection of anti-platelet serum. The circulating platelet number and concomitant mean platelet volume were measured 6 h after the injection and daily thereafter. The megakaryocyte nuclear DNA content was measured in control rabbits and after 2 h and 24 h of thrombocytopenia respectively. The observed recovery of circulating platelet number is used to construct the variation of platelet destruction rate and platelet production rate with time during thrombocytopenia. The observed rebound thrombocytosis is explained by using a balance equation of these two rates. Platelet production is linked to the megakaryocyte by physical fragmentation theory and an explanation of the observed variation of mean platelet volume is used to obtain an estimated bleeding time and circulating platelet biomass during recovery from thrombocytopenia. An interpretation is given of the homeostatic control of megakaryocytopoiesis and thrombopoiesis.

Acute Disease↗