Impronta genómica: la genética desconocida

El nacimiento de la Genética como ciencia se debió a la publicación de los trabajos de Mendel y, fundamentalmente, al redescubrimiento de sus leyes a principios del siglo XX, cuando los científicos De Vries, Correns y Tschermak llegaron a las mismas conclusiones que Mendel en 1865. Durante este siglo de vida, el concepto de herencia como transmisión de genes de una generación a la siguiente, con igual efecto a partir de cada parental, se ha venido aplicando a multitud de genes en todos los grupos de seres vivos, hasta el punto de que la Genética ha emergido como uno de los temas centrales de la Biología actual. Distintos autores, sin embargo, consideran que Mendel seleccionó cuidadosamente un grupo de caracteres en guisantes que segregaban limpiamente, mientras hay muchos otros caracteres en guisantes y en muchas otras especies que no muestran herencia mendeliana. Uno de los cambios importantes de la Genética contemporánea es explicar los caracteres y condiciones que no siguen a Mendel, así como conocer el funcionamiento de mecanismos moleculares de expresión y regulación de genes, descubiertos en las últimas décadas, entre los que se incluyen la edición del ARN y la impronta genómica. Desde este punto de vista el concepto de impronta genómica ha adquirido importancia creciente, porque puede proporcionar una explicación para un conjunto de observaciones notablemente diversas en cuanto a transmisión genética y expresión que no se ajustan a las predicciones de genes estrictamente mendelianos

Enological behaviour of biofilms formed by genetically-characterized strains of sherry flor yeast

This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License.The flor yeasts (Saccharomyces cerevisiae) form a biofilm, known as flor velum, on the surface of fino-type sherry wine at the end of the alcoholic fermentation. These film-forming yeasts are responsible for the oxidative transformation of alcohol to acetaldehyde, together with other reactions, which produce the characteristic flavours and aromas of these wines. In this study, we examine the enological behaviour of eight flor yeast strains biofilms in biological aging experiments carried out in the laboratory. Strains with identical chromosomal and mitochondrial DNA patterns and the same origin showed a more closely-related enological behaviour. But the kinetics of growth and acetaldehyde accumulation in the wine were found to be strain-dependent. Moreover, some strains were marked by high acetaldehyde accumulation in their pure cultures during the various phases of the biofilm development. These results provide valuable knowledge for planning technical strategies to improve the biological aging process in the sherry wine industry.This work was supported by PAI grant to the group BIO219.Peer reviewe

Assessment of Tools for Marker-Assisted Selection in a Marine Commercial Species: Significant Association between MSTN-1 Gene Polymorphism and Growth Traits

Growth is a priority trait from the point of view of genetic improvement. Molecular markers linked to quantitative trait loci (QTL) have been regarded as useful for marker-assisted selection in complex traits as growth. Polymorphisms have been studied in five candidate genes influencing growth in gilthead seabream (Sparus aurata): the growth hormone (GH), insulin-like growth factor-1 (IGF-1), myostatin (MSTN-1), prolactin (PRL), and somatolactin (SL) genes. Specimens evaluated were from a commercial broodstock comprising 131 breeders (from which 36 males and 44 females contributed to the progeny). In all samples eleven gene fragments, covering more than 13,000 bp, generated by PCR-RFLP, were analyzed; tests were made for significant associations between these markers and growth traits. ANOVA results showed a significant association between MSTN-1 gene polymorphism and growth traits. Pairwise tests revealed several RFLPs in the MSTN-1 gene with significant heterogeneity of genotypes among size groups. PRL and MSTN-1 genes presented linkage disequilibrium. The MSTN-1 gene was mapped in the centromeric region of a medium-size acrocentric chromosome pair

Gene mapping in the karyotype of Solea senegalensis using BAC clones

The Senegalese sole is one of the most highly valued commercial species in Southern Europe; it has attracted increasing interest particularly since the 1990's. Nevertheless, there are still unresolved problems that adversely affect its cultivation and prevent the maximum benefit being obtained from its production. The principal problems are associated with reproduction, low rates of growth in juveniles and high susceptibility to diseases, as well as high rates of mortality related to metamorphosis. Knowing the position of genes of interest in the chromosomes facilitates the construction of linkage maps and allows the chromosomes to be assigned to physical maps obtained by sequencing. This study is an initial approach to the production of a chromosome map of Solea senegalensis. The starting point for this objective is a gene library of cloned inserts in vectors capable of hosting fragments of large size: in our case, artificial chromosomes of bacteria (BAC). We have developed a protocol of single and double FISH techniques for localizing individual BAC, and have also performed double FISH for localizing two markers at the same time. Our results show the localization of BAC clones that contain genes related to the innate immune system that are important for the cultivation of this species, and genes and receptors of thyroid hormones involved in the metamorphosis of the sole. All the combinations of these genes have been analyzed by double FISH techniques to determine whether they co-localize, and also with those of gene families. Thus the first chromosome map of S. senegalensis has been obtained.&nbsp; &nbsp; &nbsp; El lenguado senegal&eacute;s es una de las especies m&aacute;s valoradas comerciales en el sur de Europa, despertando un inter&eacute;s creciente sobre todo desde la d&eacute;cada de 1990. Sin embargo, todav&iacute;a hay problemas sin resolver que afectan negativamente a su cultivo y a prevenir al m&aacute;ximo el beneficio que se obtiene a partir de su producci&oacute;n. Los principales problemas est&aacute;n relacionados con la reproducci&oacute;n, las bajas tasas de crecimiento en juveniles y alta susceptibilidad a las enfermedades, as&iacute; como las altas tasas de mortalidad relacionadas con la metamorfosis. El Conocimiento de la posici&oacute;n de los genes de inter&eacute;s en los cromosomas facilita la construcci&oacute;n de mapas de ligamiento y permite ser asignados los cromosomas a los mapas f&iacute;sicos obtenidos por secuenciaci&oacute;n. Este estudio es una primera aproximaci&oacute;n a la producci&oacute;n de un mapa cromos&oacute;mico de Solea senegalensis. </p

Evidence for 5S rDNA Horizontal Transfer in the toadfish Halobatrachus didactylus (Schneider, 1801) based on the analysis of three multigene families

Abstract Background The Batrachoididae family is a group of marine teleosts that includes several species with more complicated physiological characteristics, such as their excretory, reproductive, cardiovascular and respiratory systems. Previous studies of the 5S rDNA gene family carried out in four species from the Western Atlantic showed two types of this gene in two species but only one in the other two, under processes of concerted evolution and birth-and-death evolution with purifying selection. Here we present results of the 5S rDNA and another two gene families in Halobatrachus didactylus, an Eastern Atlantic species, and draw evolutionary inferences regarding the gene families. In addition we have also mapped the genes on the chromosomes by two-colour fluorescence in situ hybridization (FISH). Results Two types of 5S rDNA were observed, named type α and type β. Molecular analysis of the 5S rDNA indicates that H. didactylus does not share the non-transcribed spacer (NTS) sequences with four other species of the family; therefore, it must have evolved in isolation. Amplification with the type β specific primers amplified a specific band in 9 specimens of H. didactylus and two of Sparus aurata. Both types showed regulatory regions and a secondary structure which mark them as functional genes. However, the U2 snRNA gene and the ITS-1 sequence showed one electrophoretic band and with one type of sequence. The U2 snRNA sequence was the most variable of the three multigene families studied. Results from two-colour FISH showed no co-localization of the gene coding from three multigene families and provided the first map of the chromosomes of the species. Conclusions A highly significant finding was observed in the analysis of the 5S rDNA, since two such distant species as H. didactylus and Sparus aurata share a 5S rDNA type. This 5S rDNA type has been detected in other species belonging to the Batrachoidiformes and Perciformes orders, but not in the Pleuronectiformes and Clupeiformes orders. Two hypotheses have been outlined: one is the possible vertical permanence of the shared type in some fish lineages, and the other is the possibility of a horizontal transference event between ancient species of the Perciformes and Batrachoidiformes orders. This finding opens a new perspective in fish evolution and in the knowledge of the dynamism of the 5S rDNA. Cytogenetic analysis allowed some evolutionary trends to be roughed out, such as the progressive change in the U2 snDNA and the organization of (GATA)n repeats, from dispersed to localized in one locus. The accumulation of (GATA)n repeats in one chromosome pair could be implicated in the evolution of a pair of proto-sex chromosomes. This possibility could situate H. didactylus as the most highly evolved of the Batrachoididae family in terms of sex chromosome biology.This work was supported by grants from the Junta de Andalucía (Spain) to the PAI BIO-219 group (LR), CACYTMAR and the “Proyecto de excelencia” RNM-03074 (CS). MUM holds a CSIC JAE fellowship.Peer Reviewe

The genomic structure of the highlyconserved dmrt1 gene in Solea senegalensis (Kaup, 1868) shows an unexpected intragenic duplication

Knowing the factors responsible for sex determination in a species has significant theoretical and practical implications; the dmrt1 gene (Doublesex and Mab-3 (DM)-related Transcription factor 1) plays this role in diverse animal species. Solea senegalensis is a commercially important flat fish in which females grow 30% faster than males. It has 2n = 42 chromosomes and an XX / XY chromosome system for sex determination, without heteromorph chromosomes but with sex proto-chromosome. In the present study, we are providing the genomic structure and nucleotide sequence of dmrt1 gene obtained from cDNA from male and female adult gonads. A cDNA of 2027 containing an open-reading frame (ORF) of 1206 bp and encoding a 402 aa protein it is described for dmrt1 gene of S. senegalensis. Multiple mRNA isoforms indicating a high variable system of alternative splicing in the expression of dmrt1 of the sole in gonads were studied. None isoforms could be related to sex of individuals. The genomic structure of the dmrt1 of S. senegalensis showed a gene of 31400 bp composed of 7 exons and 6 introns. It contains an unexpected duplication of more than 10399 bp, involving part of the exon I, exons II and III and a SINE element found in the sequence that it is proposed as responsible for the duplication. A mature miRNA of 21 bp in length was localized at 336 bp from exon V. Protein-protein interacting networks of the dmrt1 gene showed matches with dmrt1 protein from Cynoglossus semilaevis and a protein interaction network with 11 nodes (dmrt1 plus 10 other proteins). The phylogenetic relationship of the dmrt1 gene in S. senegalensis is consistent with the evolutionary position of its species. The molecular characterization of this gene will enhance its functional analysis and the understanding of sex differentiation in Solea senegalensis and other flatfish

Evolutionary Dynamics of Multigene Families in Triportheus (Characiformes, Triportheidae): A Transposon Mediated Mechanism?

Triportheus (Characiformes, Triportheidae) is a freshwater fish genus with 18 valid species. These fishes are widely distributed in the major river drainages of South America, having commercial importance in the fishing market, mainly in the Amazon basin. This genus has diverged recently in a complex process of speciation carried out in different river basins. The use of repetitive sequences is suitable to trace the genomic reorganizations occured along the speciation process. In this work, the 5S rDNA multigene family has been characterized at molecular and phylogenetic level. The results showed that other multigene family has been found within the non-transcribed spacer (NTS): the U1 snRNA gene. Double-FISH with 5S and U1 probes were also performed, confirming the close linkage between these two multigene families. Moreover, evidences of different transposable elements (TE) were detected within the spacer, thus suggesting a transposon-mediated mechanism of 5S-U1 evolutionary pathway in this genus. Phylogenetic analysis demonstrated a species-specific grouping, except for Triportheus pantanensis, Triportheus aff. rotundatus and Triportheus trifurcatus. The evolutionary model of the 5S rDNA in Triportheus species has been discussed. In addition, the results suggest new clues for the speciation and evolutionary trend in these species, which could be suitable to use in other Characiformes species

Cytogenomics Unveil Possible Transposable Elements Driving Rearrangements in Chromosomes 2 and 4 of Solea senegalensis

Cytogenomics, the integration of cytogenetic and genomic data, has been used here to reconstruct the evolution of chromosomes 2 and 4 of Solea senegalensis. S. senegalensis is a flat fish with a karyotype comprising 2n = 42 chromosomes: 6 metacentric + 4 submetacentric + 8 subtelocentric + 24 telocentric. The Fluorescence in situ Hybridization with Bacterial Artificial Chromosomes (FISH-BAC) technique was applied to locate BACs in these chromosomes (11 and 10 BACs in chromosomes 2 and 4, respectively) and to generate integrated maps. Synteny analysis, taking eight reference fish species (Cynoglossus semilaevis, Scophthalmus maximus, Sparus aurata, Gasterosteus aculeatus, Xiphophorus maculatus, Oryzias latipes, Danio rerio, and Lepisosteus oculatus) for comparison, showed that the BACs of these two chromosomes of S. senegalensis were mainly distributed in two principal chromosomes in the reference species. Transposable Elements (TE) analysis showed significant differences between the two chromosomes, in terms of number of loci per Mb and coverage, and the class of TE (I or II) present. Analysis of TE divergence in chromosomes 2 and 4 compared to their syntenic regions in four reference fish species (C. semilaevis, S. maximus, O. latipes, and D. rerio) revealed differences in their age of activity compared with those species but less notable differences between the two chromosomes. Differences were also observed in peaks of divergence and coverage of TE families for all reference species even in those close to S. senegalensis, like S. maximus and C. semilaevis. Considered together, chromosomes 2 and 4 have evolved by Robertsonian fusions, pericentric inversions, and other chromosomal rearrangements mediated by TEs

Evolution of the Proto Sex-Chromosome in Solea senegalensis

Solea senegalensis is a flatfish belonging to the Soleidae family within the Pleuronectiformes order. It has a karyotype of 2n = 42 (FN = 60; 6M + 4 SM + 8 St + 24 T) and a XX/XY system. The first pair of metacentric chromosomes has been proposed as a proto sex-chromosome originated by a Robertsonian fusion between acrocentric chromosomes. In order to elucidate a possible evolutionary origin of this chromosome 1, studies of genomic synteny were carried out with eight fish species. A total of 88 genes annotated within of 14 BACs located in the chromosome 1 of S. senegalensis were used to elaborate syntenic maps. Six BACs (BAC5K5, BAC52C17, BAC53B20, BAC84K7, BAC56H24, and BAC48P7) were distributed in, at least, 5 chromosomes in the species studied, and a group of four genes from BAC53B20 (grsf1, rufy3, slc4a4 and np r2) and genes from BAC48K7 (dmrt2, dmrt3, dmrt1, c9orf117, kank1 and fbp1) formed a conserved cluster in all species. The analysis of repetitive sequences showed that the number of retroelements and simple repeat per BAC showed its highest value in the subcentromeric region where 53B20, 16E16 and 48K7 BACs were localized. This region contains all the dmrt genes, which are associated with sex determination in some species. In addition, the presence of a satellite “chromosome Y” (motif length: 860 bp) was detected in this region. These findings allowed to trace an evolutionary trend for the large metacentric chromosome of S. senegalensis, throughout di erent rearrangements, which could be at an initial phase of di erentiation as sex chromosome