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Marques A, Klemme S, Houben A. Evolution of Plant B Chromosome Enriched Sequences. Genes (Basel) 2018; 9:genes9100515. [PMID: 30360448 PMCID: PMC6210368 DOI: 10.3390/genes9100515] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 10/13/2018] [Accepted: 10/18/2018] [Indexed: 01/10/2023] Open
Abstract
B chromosomes are supernumerary chromosomes found in addition to the normal standard chromosomes (A chromosomes). B chromosomes are well known to accumulate several distinct types of repeated DNA elements. Although the evolution of B chromosomes has been the subject of numerous studies, the mechanisms of accumulation and evolution of repetitive sequences are not fully understood. Recently, new genomic approaches have shed light on the origin and accumulation of different classes of repetitive sequences in the process of B chromosome formation and evolution. Here we discuss the impact of repetitive sequences accumulation on the evolution of plant B chromosomes.
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Affiliation(s)
- André Marques
- Laboratory of Genetic Resources, Federal University of Alagoas, Av. Manoel Severino Barbosa, 57309-005 Arapiraca-AL, Brazil.
| | - Sonja Klemme
- Biology Centre, Czech Academy of Sciences, Institute of Plant Molecular Biology, Branišovská 31, CZ-37005 České Budějovice, Czech Republic.
| | - Andreas Houben
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466 Gatersleben, Germany.
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Jetybayev IY, Bugrov AG, Dzuybenko VV, Rubtsov NB. B Chromosomes in Grasshoppers: Different Origins and Pathways to the Modern B s. Genes (Basel) 2018; 9:genes9100509. [PMID: 30340429 PMCID: PMC6209997 DOI: 10.3390/genes9100509] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/30/2018] [Accepted: 10/17/2018] [Indexed: 01/05/2023] Open
Abstract
B chromosomes (Bs) were described in most taxa of eukaryotes and in around 11.9% of studied Orthopteran species. In some grasshopper species, their evolution has led to many B chromosome morphotypes. We studied the Bs in nine species (Nocaracris tardus, Nocaracris cyanipes, Aeropus sibiricus, Chorthippus jacobsoni, Chorthippus apricarius, Bryodema gebleri, Asiotmethis heptapotamicus songoricus, Podisma sapporensis, and Eyprepocnemis plorans), analyzing their possible origin and further development. The studied Bs consisted of C-positive or C-positive and C-negative regions. Analyzing new data and considering current hypotheses, we suggest that Bs in grasshoppers could arise through different mechanisms and from different chromosomes of the main set. We gave our special attention to the Bs with C-negative regions and suggest a new hypothesis of B chromosome formation from large or medium autosomes. This hypothesis includes dissemination of repetitive sequences and development of intercalary heterochromatic blocks in euchromatic chromosome arm followed by deletion of euchromatic regions located between them. The hypothesis is based on the findings of the Eyprepocnemis plorans specimens with autosome containing numerous intercalary repeat clusters, analysis of C-positive Bs in Eyprepocnemis plorans and Podisma sapporensis containing intercalary and terminal C-negative regions, and development of heterochromatic neo-Y chromosome in some Pamphagidae grasshoppers.
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Affiliation(s)
- Ilyas Yerkinovich Jetybayev
- The Federal Research Center Institute of Cytology and Genetics, Russian Academy of Sciences, Siberian Branch, Lavrentjev Ave., 10, 630090 Novosibirsk, Russia.
- Institute of Systematics and Ecology of Animals, Russian Academy of Sciences, Siberian Branch, Frunze str. 11, 630091 Novosibirsk, Russia.
| | - Alexander Gennadievich Bugrov
- Institute of Systematics and Ecology of Animals, Russian Academy of Sciences, Siberian Branch, Frunze str. 11, 630091 Novosibirsk, Russia.
- Novosibirsk State University, Pirogov str., 2, 630090 Novosibirsk, Russia.
| | | | - Nikolay Borisovich Rubtsov
- The Federal Research Center Institute of Cytology and Genetics, Russian Academy of Sciences, Siberian Branch, Lavrentjev Ave., 10, 630090 Novosibirsk, Russia.
- Novosibirsk State University, Pirogov str., 2, 630090 Novosibirsk, Russia.
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Karyotype Variability and Inter-Population Genomic Differences in Freshwater Ostracods (Crustacea) Showing Geographical Parthenogenesis. Genes (Basel) 2018. [PMID: 29518021 PMCID: PMC5867871 DOI: 10.3390/genes9030150] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Transitions from sexual to asexual reproduction are often associated with polyploidy and increased chromosomal plasticity in asexuals. We investigated chromosomes in the freshwater ostracod species Eucypris virens (Jurine, 1820), where sexual, asexual and mixed populations can be found. Our initial karyotyping of multiple populations from Europe and North Africa, both sexual and asexual, revealed a striking variability in chromosome numbers. This would suggest that chromosomal changes are likely to be accelerated in asexuals because the constraints of meiosis are removed. Hence, we employed comparative genomic hybridization (CGH) within and among sexual and asexual populations to get insights into E. virens genome arrangements. CGH disclosed substantial genomic imbalances among the populations analyzed, and three patterns of genome arrangement between these populations: 1. Only putative ribosomal DNA (rDNA)-bearing regions were conserved in the two populations compared indicating a high sequence divergence between these populations. This pattern is comparable with our findings at the interspecies level of comparison; 2. Chromosomal regions were shared by both populations to a varying extent with a distinct copy number variation in pericentromeric and presumable rDNA-bearing regions. This indicates a different rate of evolution in repetitive sequences; 3. A mosaic pattern of distribution of genomic material that can be explained as non-reciprocal genetic introgression and evidence of a hybrid origin of these individuals. We show an overall increased chromosomal dynamics in E. virens that is complementary with available phylogenetic and population genetic data reporting highly differentiated diploid sexual and asexual lineages with a wide variety of genetic backgrounds.
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Ruiz-Ruano FJ, Cuadrado Á, Montiel EE, Camacho JPM, López-León MD. Next generation sequencing and FISH reveal uneven and nonrandom microsatellite distribution in two grasshopper genomes. Chromosoma 2014; 124:221-34. [PMID: 25387401 DOI: 10.1007/s00412-014-0492-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2014] [Revised: 10/17/2014] [Accepted: 10/29/2014] [Indexed: 11/29/2022]
Abstract
Simple sequence repeats (SSRs), also known as microsatellites, are one of the prominent DNA sequences shaping the repeated fraction of eukaryotic genomes. In spite of their profuse use as molecular markers for a variety of genetic and evolutionary studies, their genomic location, distribution, and function are not yet well understood. Here we report the first thorough joint analysis of microsatellite motifs at both genomic and chromosomal levels in animal species, by a combination of 454 sequencing and fluorescent in situ hybridization (FISH) techniques performed on two grasshopper species. The in silico analysis of the 454 reads suggested that microsatellite expansion is not driving size increase of these genomes, as SSR abundance was higher in the species showing the smallest genome. However, the two species showed the same uneven and nonrandom location of SSRs, with clear predominance of dinucleotide motifs and association with several types of repetitive elements, mostly histone gene spacers, ribosomal DNA intergenic spacers (IGS), and transposable elements (TEs). The FISH analysis showed a dispersed chromosome distribution of microsatellite motifs in euchromatic regions, in coincidence with chromosome location patterns previously observed for many mobile elements in these species. However, some SSR motifs were clustered, especially those located in the histone gene cluster.
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Affiliation(s)
- Francisco J Ruiz-Ruano
- Departamento de Genética Facultad de Ciencias, Universidad de Granada, 18071, Granada, Spain
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Montiel EE, Cabrero J, Ruiz-Estévez M, Burke WD, Eickbush TH, Camacho JPM, López-León MD. Preferential occupancy of R2 retroelements on the B chromosomes of the grasshopper Eyprepocnemis plorans. PLoS One 2014; 9:e91820. [PMID: 24632855 PMCID: PMC3954772 DOI: 10.1371/journal.pone.0091820] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 02/14/2014] [Indexed: 02/02/2023] Open
Abstract
R2 non-LTR retrotransposons exclusively insert into the 28S rRNA genes of their host, and are expressed by co-transcription with the rDNA unit. The grasshopper Eyprepocnemis plorans contains transcribed rDNA clusters on most of its A chromosomes, as well as non-transcribed rDNA clusters on the parasitic B chromosomes found in many populations. Here the structure of the E. plorans R2 element, its abundance relative to the number of rDNA units and its retrotransposition activity were determined. Animals screened from five populations contained on average over 12,000 rDNA units on their A chromosomes, but surprisingly only about 100 R2 elements. Monitoring the patterns of R2 insertions in individuals from these populations revealed only low levels of retrotransposition. The low rates of R2 insertion observed in E. plorans differ from the high levels of R2 insertion previously observed in insect species that have many fewer rDNA units. It is proposed that high levels of R2 are strongly selected against in E. plorans, because the rDNA transcription machinery in this species is unable to differentiate between R2-inserted and uninserted units. The B chromosomes of E. plorans contain an additional 7,000 to 15,000 rDNA units, but in contrast to the A chromosomes, from 150 to over 1,500 R2 elements. The higher concentration of R2 in the inactive B chromosomes rDNA clusters suggests these chromosomes can act as a sink for R2 insertions thus further reducing the level of insertions on the A chromosomes. These studies suggest an interesting evolutionary relationship between the parasitic B chromosomes and R2 elements.
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Affiliation(s)
- Eugenia E. Montiel
- Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Granada, Spain
| | - Josefa Cabrero
- Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Granada, Spain
| | - Mercedes Ruiz-Estévez
- Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Granada, Spain
| | - William D. Burke
- Department of Biology, University of Rochester, Rochester, New York, United States of America
| | - Thomas H. Eickbush
- Department of Biology, University of Rochester, Rochester, New York, United States of America
| | - Juan Pedro M. Camacho
- Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Granada, Spain
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Cabrero J, López-León MD, Ruíz-Estévez M, Gómez R, Petitpierre E, Rufas JS, Massa B, Kamel Ben Halima M, Camacho JPM. B1 was the ancestor B chromosome variant in the western Mediterranean area in the grasshopper Eyprepocnemis plorans. Cytogenet Genome Res 2013; 142:54-8. [PMID: 24217371 DOI: 10.1159/000356052] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/19/2013] [Indexed: 11/19/2022] Open
Abstract
We analyzed the distribution of 2 repetitive DNAs, i.e. ribosomal DNA (rDNA) and a satellite DNA (satDNA), on the B chromosomes found in 17 natural populations of the grasshopper Eyprepocnemis ploransplorans sampled around the western Mediterranean region, including the Iberian Peninsula, Balearic Islands, Sicily, and Tunisia. Based on the amount of these repetitive DNAs, 4 types of B variants were found: B1, showing an equal or higher amount of rDNA than satDNA, and 3 other variants, B2, B24 and B5, bearing a higher amount of satDNA than rDNA. The variants B1 and B2 varied in size among populations: B1 was about half the size of the X chromosome in Balearic Islands, but two-thirds of the X in Iberian populations at Alicante, Murcia and Albacete provinces. Likewise, B2 was about one-third the size of the X chromosome in populations from the Granada province but half the size of the X in the populations collected at Málaga province. The widespread geographical distribution of the B1 variant makes it the best candidate for being the ancestor B chromosome in the whole western Mediterranean region.
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Affiliation(s)
- J Cabrero
- Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Granada, Spain
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Marques A, Banaei-Moghaddam AM, Klemme S, Blattner FR, Niwa K, Guerra M, Houben A. B chromosomes of rye are highly conserved and accompanied the development of early agriculture. ANNALS OF BOTANY 2013; 112:527-34. [PMID: 23739836 PMCID: PMC3718213 DOI: 10.1093/aob/mct121] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 04/16/2013] [Indexed: 05/02/2023]
Abstract
BACKGROUND AND AIMS Supernumerary B chromosomes (Bs) represent a specific type of selfish genetic element. As Bs are dispensable for normal growth, it is expected to observe B polymorphisms among populations. To address whether Bs maintained in geographically distinct populations of cultivated and weedy rye are polymorphic, the distribution patterns and the transcriptional activity of different B-located repeats were analysed. METHODS Bs of cultivated and weedy rye from seven origins were analysed by fluorescence in situ hybridization (FISH) with probes specific for the pericentromeric and interstitial regions as well as the B-specific non-disjunction control region. The DNA replication, chromatin composition and transcription behaviour of the non-disjunction regions were determined. To address whether the B-marker repeats E3900 and D1100 have diverged genotypes of different origin at the sequence level, the genomic sequences of both repeats were compared between cultivated rye and weedy rye from five different origins. KEY RESULTS B chromosomes in cultivated and weedy rye have maintained a similar molecular structure at the level of subspecies. The high degree of conservation of the non-disjunction control region regarding its transcription activity, histone composition and replication underlines the functional importance of this chromosome region for the maintenance of Bs. The conserved chromosome structure suggests a monophyletic origin of the rye B. As Bs were found in different countries, it is likely that Bs were frequently present in the seed material used in early agriculture. CONCLUSIONS The surprisingly conserved chromosome structure suggests that although the rye Bs experienced rapid evolution including multiple rearrangements at the early evolutionary stages, this process has slowed significantly and may have even ceased during its recent evolution.
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Affiliation(s)
- André Marques
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany
- Laboratory of Plant Cytogenetics and Evolution, Department of Botany, UFPE, Brazil
| | - Ali M. Banaei-Moghaddam
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany
| | - Sonja Klemme
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany
| | - Frank R. Blattner
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany
| | - Katsumasa Niwa
- Laboratory of Plant Breeding, Faculty of Agriculture, Tokyo University of Agriculture, Japan
| | - Marcelo Guerra
- Laboratory of Plant Cytogenetics and Evolution, Department of Botany, UFPE, Brazil
| | - Andreas Houben
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany
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Montiel EE, Cabrero J, Camacho JPM, López-León MD. Gypsy, RTE and Mariner transposable elements populate Eyprepocnemis plorans genome. Genetica 2012; 140:365-74. [PMID: 23073915 DOI: 10.1007/s10709-012-9686-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2012] [Accepted: 10/08/2012] [Indexed: 12/12/2022]
Abstract
We analyze here the presence and abundance of three types of transposable elements (TEs), i.e. Gypsy, RTE and Mariner, in the genome of the grasshopper Eyprepocnemis plorans. PCR experiments allowed amplification, cloning and sequencing of these elements (EploGypI, EploRTE5, EploMar20) from the E. plorans genome. Fluorescent in situ hybridization (FISH) showed that all three elements are restricted to euchromatic regions, thus being absent from the pericentromeric region of all A chromosomes, which contain a satellite DNA (satDNA) and ribosomal DNA (rDNA), and being very scarce in B chromosomes mostly made up of these two types of repetitive DNA. FISH suggested that EploGypI is the most abundant and EploMar20 is the least abundant, with EploRTE5 showing intermediate abundance. An estimation of copy number, by means of quantitative PCR, showed that EploGypI is, by far, the most abundant element, followed by EploRTE5 and EploMar20, in consistency with FISH results. RNA isolation and PCR experiments on complementary DNA (cDNA) showed the presence of transcripts for the three TE elements. The implications of the preferential location of these TE elements into euchromatin, the significance of TE abundance in the giant genome of this species, and a possible relationship between TEs and B chromosome mutability, are discussed.
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Affiliation(s)
- Eugenia E Montiel
- Departamento de Genética, Universidad de Granada, 18071 Granada, Spain
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Marques A, Klemme S, Guerra M, Houben A. Cytomolecular characterization of de novo formed rye B chromosome variants. Mol Cytogenet 2012; 5:34. [PMID: 22800712 PMCID: PMC3541114 DOI: 10.1186/1755-8166-5-34] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Accepted: 06/28/2012] [Indexed: 11/23/2022] Open
Abstract
UNLABELLED BACKGROUND B chromosomes (Bs) are dispensable elements which occur in many species including rye (Secale cereale). We determined the organization of B variants to obtain insights into the origin of B polymorphisms in rye. RESULTS The observed B variants were classified according to their morphology and in situ hybridization patterns with the B-specific repeats D1100 and CL11 into (I) long arm iso B, (II) D1100-deficient B and (III) small metacentric B variants. Long arm iso Bs are likely products of a meiotic centromere misdivision and subsequent duplication of the long arm, whereas small B variants are probably generated by chromosome breakage. Some deficient Bs experienced extensive amplification of CL11 repeats. CONCLUSIONS Both the pericentromere and the nondisjunction control region seem to be involved in the generation of rye B chromosome variants. However, due to the loss of the B-specific nondisjuction control region most of the variants generated are not capable to accumulate in a population.
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Affiliation(s)
- André Marques
- Leibniz-Institute of Plant Genetics & Crop Plant Research (IPK), 06466, Gatersleben, Germany
- Laboratory of Plant Cytogenetics and Molecular Biology, Department of Botany, UFPE, Recife, Brazil
| | - Sonja Klemme
- Leibniz-Institute of Plant Genetics & Crop Plant Research (IPK), 06466, Gatersleben, Germany
| | - Marcelo Guerra
- Laboratory of Plant Cytogenetics and Molecular Biology, Department of Botany, UFPE, Recife, Brazil
| | - Andreas Houben
- Leibniz-Institute of Plant Genetics & Crop Plant Research (IPK), 06466, Gatersleben, Germany
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Teruel M, Cabrero J, Perfectti F, Camacho JPM. B chromosome ancestry revealed by histone genes in the migratory locust. Chromosoma 2009; 119:217-25. [PMID: 20016909 DOI: 10.1007/s00412-009-0251-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2009] [Revised: 11/25/2009] [Accepted: 11/30/2009] [Indexed: 12/01/2022]
Abstract
In addition to the standard set of chromosomes (A), about 15% of eukaryote genomes carry B chromosomes. In most cases, B chromosomes behave as genomic parasites being detrimental for the individuals carrying them and prospering in natural populations because of transmission advantages (drive). B chromosomes are mostly made up of repetitive DNA sequences, especially ribosomal DNA (rDNA), satellite DNA and mobile elements. In only two cases have B chromosomes been shown to carry protein-coding genes. Although some B chromosomes seem to have derived from interspecific hybridisation, the most likely source of B chromosomes is the host genome itself, but the specific A chromosome being the B ancestor has not been identified in any B-containing species. Here, we provide strong evidence for B chromosome ancestry in the migratory locust, based on the location of genes for the H3 and H4 histones in the B chromosome and a single A chromosome pair (i.e. the eighth in order of decreasing size). The high DNA sequence similarity of A and B chromosome H3-H4 genes supports B-origin from chromosome 8. The higher variation shown by B sequences, compared to A sequences, suggests that B chromosome sequences are most likely inactive and thus less subjected to purifying selection. Estimates of time of divergence for histone genes from A and B chromosomes suggest that B chromosomes are quite old (>750,000 years), showing the B-chromosome ability to persist in natural populations for long periods of time.
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Affiliation(s)
- María Teruel
- Departamento de Genética, Universidad de Granada, 18071, Granada, Spain
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Abdelaziz M, Teruel M, Chobanov D, Camacho JPM, Cabrero J. Physical mapping of rDNA and satDNA in A and B chromosomes of the grasshopper Eyprepocnemis plorans from a Greek population. Cytogenet Genome Res 2007; 119:143-6. [PMID: 18160794 DOI: 10.1159/000109631] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Accepted: 04/05/2007] [Indexed: 11/19/2022] Open
Abstract
Adult males and females of the grasshopper Eyprepocnemis plorans from a Greek population were analysed by C-banding, silver impregnation and double FISH for two DNA probes, i.e. ribosomal DNA (rDNA) and a 180-bp tandem repeat DNA (satDNA). This population shows characteristics of rDNA location in A chromosomes that are intermediate between those previously reported for eastern (Caucasus) and western (Spain and Morocco) populations. The four rDNA clusters revealed by FISH in chromosomes X, 9, 10 and 11 in Greek specimens imply two more than the two observed in chromosomes 9 and 11 in the Caucasus, but less than the 12 observed in all chromosomes in Morocco. Remarkably, the X chromosome bears one of the new rDNA locations in Greece with respect to the Caucasus, but it appears to be inactive, in contrast to X chromosomes in western populations, which are usually active. B chromosomes were very frequent in the Greek population, and three variants differing in size were observed, all of these being largely composed of rDNA, with the exception of a small pericentromeric satDNA cluster. The high B frequency suggests that B chromosomes in this population might behave parasitically, in resemblance to Bs in western populations.
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Affiliation(s)
- M Abdelaziz
- Departamento de Genética, Universidad de Granada, Spain
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Teruel M, Cabrero J, Perfectti F, Camacho JPM. Nucleolus size variation during meiosis and NOR activity of a B chromosome in the grasshopper Eyprepocnemis plorans. Chromosome Res 2007; 15:755-65. [PMID: 17609866 DOI: 10.1007/s10577-007-1159-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2007] [Revised: 05/03/2007] [Accepted: 05/03/2007] [Indexed: 10/23/2022]
Abstract
The number of nucleoli and nucleolar area were measured in meiotic cells from males of the grasshopper Eyprepocnemis plorans collected in three natural populations. Number of nucleoli per cell showed no significant correlation among cells in different meiotic stages, but there was strong positive correlation for nucleolar area between leptotene and interkinesis cells in individuals from distant populations (Salobreña in Spain, and Smir in Morocco). No correlation was, however, observed for both parameters between the meiotic stages analysed in individuals from the population of Torrox (Spain). The number of nucleoli at leptotene was about double the number at interkinesis, as expected from the double ploidy level at leptotene and the corresponding double number of rDNA clusters. Leptotene nucleolar area, however, was about fourfold that in interkinesis, presumably due to higher requirements for ribosome biogenesis in meiosis I than meiosis II. In Torrox, diplotene cells showed a lower number of nucleoli but larger nucleolar area than in leptotene cells, suggesting an increase in nucleolus size during prophase I. Significant differences were found among populations for nucleolar area but not for number of nucleoli, the smallest nucleolar area being observed in Torrox, which is the population harbouring the most parasitic B chromosome variant. No clear effects on nucleolar area or number of nucleoli were associated with the B-chromosome number. However, B-chromosome effects on the nucleolar area were apparent in the Torrox population when data were analysed with respect to a B-chromosome odd-even pattern in leptotene and interkinesis cells. However, in diplotene cells no odd-even pattern was observed for both nucleolar parameters, suggesting that the increase in nucleolar size from leptotene to diplotene dilutes the leptotene odd-even pattern. The rDNA distally located in the B chromosome was associated with a nucleolus in 6.5% out of the 247 diplotene cells analysed. The implications of these findings are discussed in the context of B chromosomes as stress-causing genome parasites and the nucleolus as a sensor of stress.
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Affiliation(s)
- María Teruel
- Departamento de Genética, Universidad de Granada, 18071, Granada, Spain
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