Organización del genoma en el Género Mytilus

[Resumen] EL ANALISIS COMPARATIVO DE LAS TRES ESPECIES DE MEJILLON EUROPEO (MYTILUS EDULIS, M: GALLOPROVINCIALIS Y M. TROSSULUS) MEDIANTE TECNICAS CITOGENETICAS DE BANDEO C,TINCION CON NITRATO DE PLATA, TINCION CON FLUOROCROMOS Y DIGESTION IN SITU CON DIFERENTES ENDONUCLEASAS DE RESTRICCION, NOS HA PERMITIDO IDENTIFICAR POSIBLES MARCADORES CROMOSOMICOS UTILES PARA DIFERENCIAR DICHAS ESPECIES. EN LOS GENOMAS DE ESTAS ESPECIES EXISTEN POCAS REGIONES RICAS EN PARES DE BASES G+C, QUE SON COINCIDENTES CON LA LOCALIZACION DE LAS REGIONES ORGANIZADORAS DEL NUCLEOLO. HEMOS DETECTADO LA EXISTENCIA DE HETEROGENEIDAD MOLECULAR SUBYACENTE A LA HETEROCROMATINA COSTITUTIVA. EL ANALISIS DE LA RESPUESTA DE LOS CROMOSOMAS A LA DIGESTION POR LOS ISOSQUIZOMEROS HPA II - MSP I PONE DE MANIFIESTO LA EXISTENCIA DE UN CIERTO GRADO DE METILACION EN EL GENOMA DE ESTOS ORGANISMOS

Characterization of different chromatin types in “Mytilus galloprovincialis” L. after C-banding, fluorochrome and restriction endonuclease treatments

[Abstract]: In this study, we have carried out the cytogenetical characterization of “Mytilus galloprovincialis” L. (2n = 28) using conventional staining and banding techniques such as fluorochromes and restriction endonucleases treatment. Chromosome digestion with trypsin enzyme resulted in a G-banding pattern which allowed us to clearly identify and classify the chromosome pairs of “M. galloprovincialis”. C-banding and chromomycin A3 staining confirmed the existence of small amounts of constitutive heterochromatin. The treatment of samples with AluI, HaeIII, DpnI, MspI, HpaII and HinfI restriction endonucleases produced specific banding patterns which demonstrate the potential of endonucleases for chromosome banding in mussels. The results obtained allow us to describe six different types of chromatin in “M. galloprovincialis”. The type is determined by the response of the chromosomes to the different treatments. Differential digestion by the enzyme pair HpaII-MspI of specific C-band positive heterochromatic areas in some of the chromosomes suggests the presence of methylation.Ministerio de Educación y Ciencia; 88/0499MInisterio de Educación y Ciencia; 90/032

Chromosome differences between European mussel populations (genus “Mytilus”)

[Abstract]: We have analysed different populations of European mussels belonging to genus “Mytilus” in order to clarify the karyotype complements of these three species (“M. edulis”, “M. galloprovincialis” and “M. trossulus”). We have employed different cytogenetic techniques (C-banding, fluorochrome staining and Ag-NOR staining) and we have carried out chromosome measurements by using image analysis. Results obtained allow us to confirm the diploid number of these species and to detect different karyotype composition. Furthermore, we describe cytogenetical differences between larval chromosomes and gill tissue chromosomes.Xunta de Galicia; 10303B9

Chromosomal markers in three species of the genus “Mytilus” (Mollusca: Bivalvia)

[Abstract]: The analysis of C-banding, NOR and fluorochrome staining was carried out in three species of European mussel, "Mytilus edulis", "M. galloprovincialis" and "M. trossulus". The results obtained allow us to detect changes in the constitutive heterochromatin within the genus "Mytilus". The existences of chromosomal markers permit us to identify and distinguish, at the cytogenetical level, these three types of mussel.MInisterio de Educación y Ciencia; 90/032

Genetic heterogeneity in natural beds of the razor clam "Ensis siliqua" revealed by microsatellites

[Abstract] The aim of this study was to analyse the genetic diversity and population structure in the razor clam Ensis siliqua along the European Atlantic coast taking into account their recent history of exploitation and the ‘Prestige' oil spill. To this end we examined the genetic variability of microsatellite markers in 211 razor clams from five populations in Ireland, Portugal and Spain. Microsatellite data revealed a low genetic differentiation between the Spanish and Portuguese populations (FST = 0–0.032) and a moderate differentiation of these populations and the Irish samples (FST = 0.071–0.100). Although we observed changes in genetic diversity in accordance with the level of exploitation and the distribution of the oil spill, these changes were mild and not significant after Bonferroni correction. This could be the result of a genuine low impact, lack of statistical power and/or the capacity of this species to recolonize quickly after the impact of anthropogenic stressors. Supporting the latter argument we found a significant temporal heterogeneity of allelic frequencies in samples coming from the same sampling locality that could be attributed to the movement of adults or larvae from unaffected source populations

Long-term evolution of 5S ribosomal DNA seems to be driven by birth-and-death processes and selection in "Ensis" razor shells (Mollusca: Bivalvia)

[Abstract] A study of nucleotide sequence variation of 5S ribosomal DNA from six Ensis species revealed that several 5S ribosomal DNA variants, based on differences in their nontranscribed spacers (NTS), occur in Ensis genomes. The 5S rRNA gene was not very polymorphic, compared with the NTS region. The phylogenetic analyses performed showed a between-species clustering of 5S ribosomal DNA variants. Sequence divergence levels between variants were very large, revealing a lack of sequence homogenization. These results strongly suggest that the long-term evolution of Ensis 5S ribosomal DNA is driven by birth-and-death processes and selection

Temporal genetic variation of microsatellite markers in the razor clam "Ensis arcuatus" (Bivalvia: Pharidae)

[Abstract] The aim of this study was to characterize new microsatellite loci in the razor clam Ensis arcuatus (Bivalvia: Pharidae) and examine the temporal genetic variability of a natural bed in Cies Islands (Galicia, north-western Spain) exploited by apnoea divers and affected by the ‘Prestige’ oil tanker spill in November 2002. In this work, we characterized four polymorphic microsatellites using an alternative approach that relies on the amplification and sequencing of ISSR markers. Observed heterozygosities ranged from 0.1053–0.6800 and number of alleles from 4–19. Linkage equilibrium was observed in all loci and two of them showed significant deviations from Hardy–Weinberg equilibrium. Estimators of FST between samples were low (<0.05) and not different from zero with a confidence level of 5%. We did not detect a clear decreasing tendency in genetic diversity although we found a significant change in allelic frequencies among samples (P = 0.0024) after the ‘Prestige’ oil spill. We propose that both phenomena could be related to a high variance in genetic success and/or a movement of adults or larvae from different source populations.Xunta de Galicia; PGIDT03PXIB10302PRXunta de Galicia; PGIDT03MA10301PRXunta de Galicia; IN840DXunta de Galicia; IN809

Analysis of ITS1 and ITS2 sequences in "Ensis" razor shells: suitability as molecular markers at the population and species levels, and evolution of these ribosomal DNA spacers

[Abstract] Internal transcribed spacer 1 and 2 (ITS1 and ITS2) sequences were analysed in Ensis razor shells (Mollusca: Bivalvia: Pharidae). We aimed to (1) test ITS1 and ITS2 as molecular markers at the population level in the successful alien E. directus (Conrad, 1843); (2) test these spacers at the species level in E. directus and three other Ensis species, E. siliqua (L., 1758), E. macha (Molina, 1782), and E. magnus (Schumacher, 1817); and (3) analyse the evolutionary processes that may be shaping Ensis ITS1 and ITS2 extant variation. In E. directus, despite the intragenomic divergence detected, ITS1 and ITS2 were informative in differentiating the geographic areas considered (Denmark and Canada) by means of both the insertion-deletion polymorphism and the nucleotide polymorphism. In this species, the 5.8S ribosomal gene (5.8S) showed scarce polymorphism. At the species level, maximum parsimony and maximum likelihood analyses revealed that ITS1 and ITS2 may be suitable to reconstruct Ensis phylogenetic relationships. Finally, the evolutionary models that best fit the long-term evolution of Ensis ITS1–5.8S–ITS2 are discussed. A mixed process of concerted evolution, birth-and-death evolution, and selection is chosen as an option that may reconcile the long-term evolution of Ensis ITS1–5.8S–ITS2 and 5S ribosomal DNA

Polyploidy in a Natural Population of Mussel, Mytilus Trossulus

[Abstract] We have analyzed natural polyploidy in a population of “Mytilus trossulus” from Vancouver Island (British Columbia, Canada) by means of cytogenetic techniques. Results obtained are the first reporting on this type of numerical chromosome aberrations in mussels.Natural Sciences and Engineering Research Council of Canada (NSERC); OGP0046399Xunta de Galicia; 10303B93Xunta de Galicia; 10306B9