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Genes, 12
December, 2020

A Comprehensive Integrated Genetic Map of the Complete Karyotype of Solea senegalensis (Kaup 1858).

Merlo, Manuel A., Portela-Bens, Silvia, Rodríguez, María E., García-Angulo, Aglaya, Cross, Ismael, Arias-Pérez, Alberto, García, Emilio, Rebordinos, Laureana

<p>aquaculture production has experienced a great increase in the last decade and, consequently, the genome knowledge of the species is gaining attention. In this sense, obtaining a high-density genome mapping of the species could offer clues to the aquaculture improvement in those aspects not resolved so far. In the present article, a review and new processed data have allowed to obtain a high-density BAC-based cytogenetic map of beside the analysis of the sequences of such BAC clones to achieve integrative data. A total of 93 BAC clones were used to localize the chromosome complement of the species and 588 genes were annotated, thus almost reaching the 2.5% of the genome sequences. As a result, important data about its genome organization and evolution were obtained, such as the lesser gene density of the large metacentric pair compared with the other metacentric chromosomes, which supports the theory of a sex proto-chromosome pair. In addition, chromosomes with a high number of linked genes that are conserved, even in distant species, were detected. This kind of result widens the knowledge of this species' chromosome dynamics and evolution.</p>

Digital object identifier (DOI): 10.3390/genes12010049

Molecular ecology
July, 2020

Adaptive divergence across Southern Ocean gradients in the pelagic diatom Fragilariopsis kerguelensis.

Postel, Ute, Glemser, Barbara, Salazar Alekseyeva, Katherine, Eggers, Sarah Lena, Groth, Marco, Glöckner, Gernot, John, Uwe, Mock, Thomas, Klemm, Kerstin, Valentin, Klaus, Beszteri, Bánk

The Southern Ocean is characterized by longitudinal water circulations crossed by strong latitudinal gradients. How this oceanographic background shapes planktonic populations is largely unknown, despite the significance of this region for global biogeochemical cycles. Here, we show, based on genomic, morphometric, ecophysiological and mating compatibility data, an example of ecotypic differentiation and speciation within an endemic pelagic inhabitant, the diatom Fragilariopsis kerguelensis. We discovered three genotypic variants, one present throughout the latitudinal transect sampled, the others restricted to the north and south, respectively. The latter two showed reciprocal monophyly across all three genomes and significant ecophysiological differences consistent with local adaptation, but produced viable offspring in laboratory crosses. The third group was also reproductively isolated from the latter two. We hypothesize that this pattern originated by an adaptive expansion accompanied by ecotypic divergence, followed by sympatric speciation.

Digital object identifier (DOI): 10.1111/mec.15554

Genes, 11
July, 2020

Deciphering the Impact of a Bacterial Infection on Meiotic Recombination in Arabidopsis with Fluorescence Tagged Lines.

Gratias, Ariane, Geffroy, Valérie

<p>Plants are under strong evolutionary pressure to maintain surveillance against pathogens. One major disease resistance mechanism is based on NB-LRR (NLR) proteins that specifically recognize pathogen effectors. The cluster organization of the NLR gene family could favor sequence exchange between NLR genes via recombination, favoring their evolutionary dynamics. Increasing data, based on progeny analysis, suggest the existence of a link between the perception of biotic stress and the production of genetic diversity in the offspring. This could be driven by an increased rate of meiotic recombination in infected plants, but this has never been strictly demonstrated. In order to test if pathogen infection can increase DNA recombination in pollen meiotic cells, we infected Fluorescent Tagged Lines (FTL) with the virulent bacteria . We measured the meiotic recombination rate in two regions of chromosome 5, containing or not an NLR gene cluster. In all tested intervals, no significant difference in genetic recombination frequency between infected and control plants was observed. Although it has been reported that pathogen exposure can sometimes increase the frequency of recombinant progeny in plants, our findings suggest that meiotic recombination rate in may be resilient to at least some pathogen attack. Alternative mechanisms are discussed.</p>

Digital object identifier (DOI): 10.3390/genes11070832

Genes, 11
June, 2020

Interstitial Telomeric Repeats Are Rare in Turtles.

Clemente, Lorenzo, Mazzoleni, Sofia, Pensabene Bellavia, Eleonora, Augstenová, Barbora, Auer, Markus, Praschag, Peter, Protiva, Tomáš, Velenský, Petr, Wagner, Philipp, Fritz, Uwe, Kratochvíl, Lukáš, Rovatsos, Michail

<p>Telomeres are nucleoprotein complexes protecting chromosome ends in most eukaryotic organisms. In addition to chromosome ends, telomeric-like motifs can be accumulated in centromeric, pericentromeric and intermediate (i.e., between centromeres and telomeres) positions as so-called interstitial telomeric repeats (ITRs). We mapped the distribution of (TTAGGG) repeats in the karyotypes of 30 species from nine families of turtles using fluorescence in situ hybridization. All examined species showed the expected terminal topology of telomeric motifs at the edges of chromosomes. We detected ITRs in only five species from three families. Combining our and literature data, we inferred seven independent origins of ITRs among turtles. ITRs occurred in turtles in centromeric positions, often in several chromosomal pairs, in a given species. Their distribution does not correspond directly to interchromosomal rearrangements. Our findings support that centromeres and non-recombining parts of sex chromosomes are very dynamic genomic regions, even in turtles, a group generally thought to be slowly evolving. However, in contrast to squamate reptiles (lizards and snakes), where ITRs were found in more than half of the examined species, and birds, the presence of ITRs is generally rare in turtles, which agrees with the expected low rates of chromosomal rearrangements and rather slow karyotype evolution in this group.</p>

Digital object identifier (DOI): 10.3390/genes11060657

BMC plant biology, 19, 183
May, 2019

Development and characterisation of interspecific hybrid lines with genome-wide introgressions from Triticum timopheevii in a hexaploid wheat background.

Devi, Urmila, Grewal, Surbhi, Yang, Cai-Yun, Hubbart-Edwards, Stella, Scholefield, Duncan, Ashling, Stephen, Burridge, Amanda, King, Ian P, King, Julie

Triticum timopheevii (2n = 4x = 28; A<sup>t</sup>A<sup>t</sup>GG), is an important source for new genetic variation for wheat improvement with genes for potential disease resistance and salt tolerance. By generating a range of interspecific hybrid lines, T. timopheevii can contribute to wheat's narrow gene-pool and be practically utilised in wheat breeding programmes. Previous studies that have generated such introgression lines between wheat and its wild relatives have been unable to use high-throughput methods to detect the presence of wild relative segments in such lines. A whole genome introgression approach, exploiting homoeologous recombination in the absence of the Ph1 locus, has resulted in the transfer of different chromosome segments from both the A and G genomes of T. timopheevii into wheat. These introgressions have been detected and characterised using single nucleotide polymorphism (SNP) markers present on a high-throughput Axiom® Genotyping Array. The analysis of these interspecific hybrid lines has resulted in the detection of 276 putative unique introgressions from T. timopheevii, thereby allowing the generation of a genetic map of T. timopheevii containing 1582 SNP markers, spread across 14 linkage groups representing each of the seven chromosomes of the A and G genomes of T. timopheevii. The genotyping of the hybrid lines was validated through fluorescence in situ hybridisation (FISH). Comparative analysis of the genetic map of T. timopheevii and the physical map of the hexaploid wheat genome showed that synteny between the two species is highly conserved at the macro-level and confirmed the presence of inter- and intra-genomic translocations within the A and G genomes of T. timopheevii that have been previously only detected through cytological techniques. In this work, we report a set of SNP markers present on a high-throughput genotyping array, able to detect the presence of T. timopheevii in a hexaploid wheat background making it a potentially valuable tool for marker assisted selection (MAS) in wheat pre-breeding programs. These valuable resources of high-density molecular markers and wheat-T. timopheevii hybrid lines will greatly enhance the work being undertaken for wheat improvement through wild relative introgressions.

Digital object identifier (DOI): 10.1186/s12870-019-1785-z

Microbiological research, 221, 28–35
April, 2019

Muscodor brasiliensis sp. nov. produces volatile organic compounds with activity against Penicillium digitatum.

Pena, Lorena C, Jungklaus, Gustavo H, Savi, Daiani C, Ferreira-Maba, Lisandra, Servienski, André, Maia, Beatriz H L N S, Annies, Vinicius, Galli-Terasawa, Lygia V, Glienke, Chirlei, Kava, Vanessa

Endophytic fungi belonging to Muscodor genus are considered as promising alternatives to be used in biological control due to the production of volatile organic compounds (VOCs). The strains LGMF1255 and LGMF1256 were isolated from the medicinal plant Schinus terebinthifolius and, by morphological data and phylogenetic analysis, identified as belonging to Muscodor genus. Phylogenetic analysis suggests that strain LGMF1256 is a new species, which is herein introduced as Muscodor brasiliensis sp. nov. The analysis of VOCs production revealed that compounds phenylethyl alcohol, α-curcumene, and E (β) farnesene until now has been reported only from M. brasiliensis, data that supports the classification of strain LGMF1256 as a new species. M. brasiliensis completely inhibited the phytopathogen P. digitatum in vitro. We also evaluated the ability of VOCs from LGMF1256 to inhibit the development of green mold symptoms by inoculation of P. digitatum in detached oranges. M. brasiliensis reduced the severity of diseases in 77%, and showed potential to be used for fruits storage and transportation to prevent the green mold symptoms development, eventually reducing the use of fungicides.

Digital object identifier (DOI): 10.1016/j.micres.2019.01.002

Journal of applied genetics, 60, 63–70
February, 2019

Structural and copy number chromosome abnormalities in canine cutaneous mast cell tumours.

Vozdova, Miluse, Kubickova, Svatava, Cernohorska, Halina, Fröhlich, Jan, Fictum, Petr, Rubes, Jiri

Mast cell tumours (MCTs) are the most common skin tumours in dogs. Their clinical behaviour is variable and their aetiology remains largely unknown. We performed a metaphase fluorescence in situ hybridisation (FISH) with whole chromosome painting probes, and interphase FISH with BAC probes for 14 cancer-related genes to reveal clonal structural chromosome rearrangements and copy number variants (CNVs) in canine cutaneous MCTs. The metaphase FISH performed in three MCTs revealed several clonal monosomies and trisomies and two different chromosome rearrangements. No centric fusions were detected. The interphase FISH showed a variety of low frequency CNVs for the individual cancer-related genes. The heterogeneous character of the detected abnormalities indicates increased chromosome instability in canine MCTs. The clonal gain of chromosome 11 was detected in 81% (13/16) of the MCTs. Further research is needed to evaluate the significance of this abnormality as prognostic factor for the survival time or recurrence risk assessments in canine cutaneous MCTs.

Digital object identifier (DOI): 10.1007/s13353-018-0471-4

TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik, 131, 389–406
February, 2018

Characterisation of Thinopyrum bessarabicum chromosomes through genome-wide introgressions into wheat.

Grewal, Surbhi, Yang, Caiyun, Edwards, Stella Hubbart, Scholefield, Duncan, Ashling, Stephen, Burridge, Amanda J, King, Ian P, King, Julie

Genome-wide introgressions of Thinopyrum bessarabicum into wheat resulted in 12 recombinant lines. Cytological and molecular techniques allowed mapping of 1150 SNP markers across all seven chromosomes of the J genome. Thinopyrum bessarabicum (2n = 2x = 14, JJ) is an important source for new genetic variation for wheat improvement due to its salinity tolerance and disease resistance. Its practical utilisation in wheat improvement can be facilitated through development of genome-wide introgressions leading to a variety of different wheat-Th . bessarabicum translocation lines. In this study, we report the generation of 12 such wheat-Th . bessarabicum recombinant lines, through two different crossing strategies, which were characterized using sequential single colour and multi-colour genomic in situ hybridization (sc-GISH and mc-GISH), multi-colour fluorescent in situ hybridization (mc-FISH) and single nucleotide polymorphic (SNP) DNA markers. We also detected 13 lines containing different Th. bessarabicum chromosome aberrations through sc-GISH. Through a combination of molecular and cytological analysis of all the 25 lines containing Th. bessarabicum recombinants and chromosome aberrations we were able to physically map 1150 SNP markers onto seven Th. bessarabicum J chromosomes which were divided into 36 segmental blocks. Comparative analysis of the physical map of Th. bessarabicum and the wheat genome showed that synteny between the two species is highly conserved at the macro-level and confirmed that Th. bessarabicum contains the 4/5 translocation also present in the A genome of wheat. These wheat-Th . bessarabicum recombinant lines and SNP markers provide a useful genetic resource for wheat improvement with the latter having a wider impact as a tool for detection of introgressions from other Thinopyrum species containing the J or a closely-related genome such as Thinopyrum intermedium (J<sup>r</sup>J<sup>r</sup>J<sup>vs</sup>J<sup>vs</sup>StSt) and Thinopyrum elongatum (E<sup>e</sup>E<sup>e</sup>), respectively.

Digital object identifier (DOI): 10.1007/s00122-017-3009-y

Scientific reports, 8, 3122
February, 2018

Phaeophleospora vochysiae Savi & Glienke sp. nov. Isolated from Vochysia divergens Found in the Pantanal, Brazil, Produces Bioactive Secondary Metabolites.

Savi, Daiani C, Shaaban, Khaled A, Gos, Francielly Maria Wilke Ramos, Ponomareva, Larissa V, Thorson, Jon S, Glienke, Chirlei, Rohr, Jürgen

Microorganisms associated with plants are highly diverse and can produce a large number of secondary metabolites, with antimicrobial, anti-parasitic and cytotoxic activities. We are particularly interested in exploring endophytes from medicinal plants found in the Pantanal, a unique and widely unexplored wetland in Brazil. In a bio-prospecting study, strains LGMF1213 and LGMF1215 were isolated as endophytes from Vochysia divergens, and by morphological and molecular phylogenetic analyses were characterized as Phaeophleospora vochysiae sp. nov. The chemical assessment of this species reveals three major compounds with high biological activity, cercoscosporin (1), isocercosporin (2) and the new compound 3-(sec-butyl)-6-ethyl-4,5-dihydroxy-2-methoxy-6-methylcyclohex-2-enone (3). Besides the isolation of P. vochysiae as endophyte, the production of cercosporin compounds suggest that under specific conditions this species causes leaf spots, and may turn into a pathogen, since leaf spots are commonly caused by species of Cercospora that produce related compounds. In addition, the new compound 3-(sec-butyl)-6-ethyl-4,5-dihydroxy-2-methoxy-6-methylcyclohex-2-enone showed considerable antimicrobial activity and low cytotoxicity, which needs further exploration.

Digital object identifier (DOI): 10.1038/s41598-018-21400-2

Journal of phycology
2018

Quantitative comparison of taxa and taxon concepts in the diatom genus Fragilariopsis: a case study on using slide scanning, multi-expert image annotation and image analysis in taxonomy.

Beszteri, Bánk, Allen, Claire, Almandoz, Gastón O, Armand, Leanne, Barcena, María Ángeles, Cantzler, Hannelore, Crosta, Xavier, Esper, Oliver, Jordan, Richard W, Kauer, Gerhard, Klaas, Christine, Kloster, Michael, Leventer, Amy, Pike, Jennifer, Rigual Hernández, Andrés S

Semi-automated methods for microscopic image acquisition, image analysis and taxonomic identification have repeatedly received attention in diatom analysis. Less well studied is the question whether and how such methods might prove useful for clarifying the delimitation of species that are difficult to separate for human taxonomists. To try to answer this question, three very similar Fragilariopsis species endemic to the Southern Ocean were targeted in this study: F. obliquecostata, F. ritscheri, and F. sublinearis. A set of 501 extended focus depth specimen images were obtained using a standardized, semi-automated microscopic procedure. Twelve diatomists independently identified these specimen images in order to reconcile taxonomic opinions and agree upon a taxonomic gold standard. Using image analyses, we then extracted morphometric features representing taxonomic characters of the target taxa. The discriminating ability of individual morphometric features was tested visually and statistically, and multivariate classification experiments were performed to test the agreement of the quantitatively-defined taxa assignments with expert consensus opinion. Beyond an updated differential diagnosis of the studied taxa, our study also shows that automated imaging and image analysis procedures for diatoms are coming close to reaching a broad applicability for routine use. This article is protected by copyright. All rights reserved.

Digital object identifier (DOI): 10.1111/jpy.12767

Sexual development : genetics, molecular biology, evolution, endocrinology, embryology, and pathology of sex determination and differentiation
2018

Triploid Colubrid Snake Provides Insight into the Mechanism of Sex Determination in Advanced Snakes.

Rovatsos, Michail, Augstenová, Barbora, Altmanová, Marie, Sloboda, Michal, Kodym, Petr, Kratochvíl, Lukáš

The advanced snakes (Caenophidia), the important amniote lineage encompassing more than 3,000 living species, possess highly conserved female heterogamety across all families. However, we still lack any knowledge on the gene(s) and the molecular mechanism controlling sex determination. Triploid individuals spontaneously appear in populations of diploid species and can provide an important insight into the evolution of sex determination. Here, we report a case of spontaneous triploidy in a male of the twin-spotted ratsnake (Elaphe bimaculata) with ZZW sex chromosomes. We speculate that as both ZZ and ZZW individuals develop male gonads, the ratio between the number of Z chromosomes and autosomes, and not the presence of the W chromosome in the genome, drives sex determination in the advanced snakes.

Digital object identifier (DOI): 10.1159/000490124

Evolution; international journal of organic evolution
2018

ZW, XY, and yet ZW: Sex chromosome evolution in snakes even more complicated.

Augstenová, Barbora, Johnson Pokorná, Martina, Altmanová, Marie, Frynta, Daniel, Rovatsos, Michail, Kratochvíl, Lukáš

Snakes are historically important in the formulation of several central concepts on the evolution of sex chromosomes. For over 50 years, it was believed that all snakes shared the same ZZ/ZW sex chromosomes, which are homomorphic and poorly differentiated in "basal" snakes such as pythons and boas, while heteromorphic and well differentiated in "advanced" (caenophidian) snakes. Recent molecular studies revealed that differentiated sex chromosomes are indeed shared among all families of caenophidian snakes, but that boas and pythons evolved likely independently male heterogamety (XX/XY sex chromosomes). The historical report of heteromorphic ZZ/ZW sex chromosomes in a boid snake was previously regarded as ambiguous. In the current study, we document heteromorphic ZZ/ZW sex chromosomes in a boid snake. A comparative approach suggests that these heteromorphic sex chromosomes evolved very recently and that they are poorly differentiated at the sequence level. Interestingly, two snake lineages with confirmed male heterogamety possess homomorphic sex chromosomes, but heteromorphic sex chromosomes are present in both snake lineages with female heterogamety. We point out that this phenomenon is more common across squamates. The presence of female heterogamety in non-caenophidian snakes indicates that the evolution of sex chromosomes in this lineage is much more complex than previously thought, making snakes an even better model system for the evolution of sex chromosomes.

Digital object identifier (DOI): 10.1111/evo.13543

Nucleic acids research, 45, 1860–1871
February, 2017

RMI1 and TOP3α limit meiotic CO formation through their C-terminal domains.

Séguéla-Arnaud, Mathilde, Choinard, Sandrine, Larchevêque, Cécile, Girard, Chloé, Froger, Nicole, Crismani, Wayne, Mercier, Raphael

At meiosis, hundreds of programmed DNA double-strand breaks (DSBs) form and are repaired by homologous recombination. From this large number of DSBs, only a subset yields crossovers (COs), with a minimum of one CO per chromosome pair. All DSBs must be repaired and every recombination intermediate must be resolved to avoid subsequent entanglement and chromosome breakage. The conserved BLM-TOP3α-RMI1 (BTR) complex acts on early and late meiotic recombination intermediates to both limit CO outcome and promote chromosome integrity. In Arabidopsis, the BLM homologues RECQ4A and RECQ4B act redundantly to prevent meiotic extra COs, but recombination intermediates are fully resolved in their absence. In contrast, TOP3α is needed for both processes. Here we show through the characterization of specific mutants that RMI1 is a major anti-CO factor, in addition to being essential to prevent chromosome breakage and entanglement. Further, our findings suggest a specific role of the C-terminal domains of RMI1 and TOP3α, that respectively contain an Oligo Binding domain (OB2) and ZINC finger motifs, in preventing extra-CO. We propose that these domains of TOP3α and RMI1 define a sub-domain of the BTR complex which is dispensable for the resolution of recombination intermediates but crucial to limit extra-COs.

Digital object identifier (DOI): 10.1093/nar/gkw1210

Animal science journal = Nihon chikusan Gakkaiho, 88, 27–32
January, 2017

Comparative genomic hybridization in detection of DNA changes in canine lymphomas.

Drážovská, Monika, Šiviková, Katarína, Dianovský, Ján, Horňák, Miroslav

In this study, chromosomal imbalances in tumor tissues (lymphomas) and nucleotide changes in tumor suppressor TP53 were studied in a Bernese Mountain dog bitch and a cross breed bitch. Using comparative genomic hybridization, numerous chromosomal rearrangements were detected, which indicated the heterogeneity in tumor growth: in the cross breed bitch, a deletion on the chromosome 9, and duplications on chromosomes 5, 8 and 17 have been found. In the Bernese Mountain Dog bitch, losses on chromosomes 1, 5, 8, 12, 18, 22, 27, 29 and gains on chromosomes 1, 2, 9, 11, 15, 16, 18, 20, 23, 24, 25, 28, 29, 30, 34, 36, 37 and 38 were identified. With the sequencing of the TP53 gene, one silent mutation, transition A/G at position 138 in exon 5 was detected, without changing the amino acid.

Digital object identifier (DOI): 10.1111/asj.12582

Appl. Sci., 7, 330
2017

Large-Scale Permanent Slide Imaging and Image Analysis for Diatom Morphometrics

Michael Kloster, Oliver Esper, Gerhard Kauer, Bánk Beszteri

Light microscopy analysis of diatom frustules is widely used in basic and applied research, notably taxonomy, morphometrics, water quality monitoring and paleo-environmental studies. Although there is a need for automation in these applications, various developments in image processing and analysis methodology supporting these tasks have not become widespread in diatom-based analyses. We have addressed this issue by combining our automated diatom image analysis software SHERPA with a commercial slide-scanning microscope. The resulting workflow enables mass-analyses of a broad range of morphometric features from individual frustules mounted on permanent slides. Extensive automation and internal quality control of the results helps to minimize user intervention, but care was taken to allow the user to stay in control of the most critical steps (exact segmentation of valve outlines and selection of objects of interest) using interactive functions for reviewing and revising results. In this contribution, we describe our workflow and give an overview of factors critical for success, ranging from preparation and mounting through slide scanning and autofocus finding to final morphometric data extraction. To demonstrate the usability of our methods we finally provide an example application by analysing Fragilariopsis kerguelensis valves originating from a sediment core, which substantially extends the size range reported in the literature.

Digital object identifier (DOI): 10.3390

Chromosome Res
May, 2016

Karyotype diversity suggests that Laonastes aenigmamus (Laotian rock rat) (Rodentia, Diatomyidae) is a multi-specific genus.

Richard, Florence, Gerbault-Seureau, Michèle, Douangboupha, Bounneuang, Keovichit, Kham, Hugot, Jean-Pierre, Dutrillaux, Bernard

Laonastes aenigmamus (Khanyou) is a recently described rodent species living in geographically separated limestone formations of the Khammuan Province in Lao PDR. Chromosomes of 21 specimens of L. aenigmamus were studied using chromosome banding as well as fluorescent in situ hybridization (FISH) techniques using human painting, telomere repeats, and 28S rDNA probes. Four different karyotypes were established. Study with human chromosome paints and FISH revealed that four large chromosomes were formed by multiple common tandem fusions, with persistence of some interstitial telomeres. The rearrangements separating the different karyotypes (I to IV) were also reconstructed. Various combinations of Robertsonian translocations or tandem fusions involving the same chromosomes differentiate these karyotypes. These rearrangements create a strong gametic barrier, which isolates specimens with karyotype II from the others. C-banding and FISH with telomere repeats also exhibit large and systematized differences between karyotype II and others. These data indicate an ancient reproductive separation and suggest that Laonastes is not a mono-specific genus.

Digital object identifier (DOI): 10.1007/s10577-016-9527-7

Reprod Domest Anim, 51(1), 171–174
February, 2016

A Non-Reciprocal Autosomal Translocation 64,XX, t(4;10)(q21;p15) in an Arabian Mare with Repeated Early Embryonic Loss.

Ghosh, S., Das, P. J., Avila, F., Thwaits, B. K., Chowdhary, B. P., Raudsepp, T.

Balanced autosomal translocations are a known cause for repeated early embryonic loss (REEL) in horses. In most cases, carriers of such translocations are phenotypically normal, but the chromosomal aberration negatively affects gametogenesis giving rise to both genetically balanced and unbalanced gametes. The latter, if involved in fertilization, result in REEL, whereas gametes with the balanced form of translocation will pass the defect into next generation. Therefore, in order to reduce the incidence of REEL, identification of translocation carriers is critical. Here, we report about a phenotypically normal 3-year-old Arabian mare that had repeated resorption of conceptuses prior to day 45 of gestation and was diagnosed with REEL. Conventional and molecular cytogenetic analyses revealed that the mare had normal chromosome number 64,XX but carried a non-mosaic and non-reciprocal autosomal translocation t(4;10)(q21;p15). This is a novel translocation described in horses with REEL and the first such report in Arabians. Previous cases of REEL due to autosomal translocations have exclusively involved Thoroughbreds. The findings underscore the importance of routine cytogenetic screening of breeding animals.

Digital object identifier (DOI): 10.1111/rda.12636

Comp Cytogenet, 10(1), 45–59
2016

Sex chromosome diversity in Armenian toad grasshoppers (Orthoptera, Acridoidea, Pamphagidae).

Bugrov, Alexander G., Jetybayev, Ilyas E., Karagyan, Gayane H., Rubtsov, Nicolay B.

Although previous cytogenetic analysis of Pamphagidae grasshoppers pointed to considerable karyotype uniformity among most of the species in the family, our study of species from Armenia has discovered other, previously unknown karyotypes, differing from the standard for Pamphagidae mainly in having unusual sets of sex chromosomes. Asiotmethis turritus (Fischer von Waldheim, 1833), Paranocaracris rubripes (Fischer von Waldheim, 1846), and Nocaracris cyanipes (Fischer von Waldheim, 1846) were found to have the karyotype 2n♂=16+neo-XY and 2n♀=16+neo-XX, the neo-X chromosome being the result of centromeric fusion of an ancient acrocentric X chromosome and a large acrocentric autosome. The karyotype of Paranothrotes opacus (Brunner von Wattenwyl, 1882) was found to be 2n♂=14+X1X2Y and 2n♀=14+X1X1X2X2., the result of an additional chromosome rearrangement involving translocation of the neo-Y and another large autosome. Furthermore, evolution of the sex chromosomes in these species has involved different variants of heterochromatinization and miniaturization of the neo-Y. The karyotype of Eremopeza festiva (Saussure, 1884), in turn, appeared to have the standard sex determination system described earlier for Pamphagidae grasshoppers, 2n♂=18+X0 and 2n♀=18+XX, but all the chromosomes of this species were found to have small second C-positive arms. Using fluorescent in situ hybridization (FISH) with 18S rDNA and telomeric (TTAGG)n DNA repeats to yield new data on the structural organization of chromosomes in the species studied, we found that for most of them, clusters of repeats homologous to 18S rDNA localize on two, three or four pairs of autosomes and on the X. In Eremopeza festiva, however, FISH with labelled 18S rDNA painted C-positive regions of all autosomes and the X chromosome; clusters of telomeric repeats localized primarily on the ends of the chromosome arms. Overall, we conclude that the different stages of neo-Y degradation revealed in the Pamphagidae species studied make the family a very promising and useful model for studying sex chromosome evolution.

Digital object identifier (DOI): 10.3897/CompCytogen.v10i1.6407

Genet Sel Evol, 48, 12
2016

The second highest chromosome count among vertebrates is observed in cultured sturgeon and is associated with genome plasticity.

Havelka, Miloš, Bytyutskyy, Dmytro, Symonová, Radka, Ráb, Petr, Flaj\vshans, Martin

<p>One of the five basal actinopterygian lineages, the Chondrostei, including sturgeon, shovelnose, and paddlefish (Order Acipenseriformes) show extraordinary ploidy diversity associated with three rounds of lineage-specific whole-genome duplication, resulting in three levels of ploidy in sturgeon. Recently, incidence of spontaneous polyploidization has been reported among cultured sturgeon and it could have serious negative implications for the economics of sturgeon farming. We report the occurrence of seven spontaneous heptaploid (7n) Siberian sturgeon Acipenser baerii, which is a functional tetraploid species (4n) with ~245 chromosomes. Our aims were to assess ploidy level and chromosome number of the analysed specimens and to identify the possible mechanism that underlies the occurrence of spontaneous additional chromosome sets in their genome.Among 150 specimens resulting from the mating of a tetraploid (4n) A. baerii (~245 chromosomes) dam with a hexaploid (6n) A. baerii (~368 chromosomes) sire, 143 displayed a relative DNA content that corresponds to pentaploidy (5n) with an absolute DNA content of 8.98 ± 0.03 pg DNA per nucleus and nuclear area of 35.3 ± 4.3 μm(2) and seven specimens exhibited a relative DNA content that corresponds to heptaploidy (7n), with an absolute DNA content of 15.02 ± 0.04 pg DNA per nucleus and nuclear area of 48.4 ± 5.1 μm(2). Chromosome analyses confirmed a modal number of ~437 chromosomes in these heptaploid (7n) individuals. DNA genotyping of eight microsatellite loci followed by parental assignment confirmed spontaneous duplication of the maternal chromosome sets via retention of the second polar body in meiosis II as the mechanism for the formation of this unusual chromosome number and ploidy level in a functional tetraploid A. baerii.We report the second highest chromosome count among vertebrates in cultured sturgeon (~437) after the schizothoracine cyprinid Ptychobarbus dipogon with ~446 chromosomes. The finding also represents the highest documented chromosome count in Acipenseriformes, and the first report of a functional heptaploid (7n) genome composition in sturgeon. To our knowledge, this study provides the first clear evidence of a maternal origin for spontaneous polyploidization in cultured A. baerii. To date, all available data indicate that spontaneous polyploidization occurs frequently among cultured sturgeons.</p>

Digital object identifier (DOI): 10.1186/s12711-016-0194-0

Proc Natl Acad Sci U S A, 112(15), 4713–4718
April, 2015

Multiple mechanisms limit meiotic crossovers: TOP3alpha and two BLM homologs antagonize crossovers in parallel to FANCM.

Séguéla-Arnaud, Mathilde, Crismani, Wayne, Larchevêque, Cécile, Mazel, Julien, Froger, Nicole, Choinard, Sandrine, Lemhemdi, Afef, Macaisne, Nicolas, Van Leene, Jelle, Gevaert, Kris, De Jaeger, Geert, Chelysheva, Liudmilla, Mercier, Raphael

Meiotic crossovers (COs) have two important roles, shuffling genetic information and ensuring proper chromosome segregation. Despite their importance and a large excess of precursors (i.e., DNA double-strand breaks, DSBs), the number of COs is tightly regulated, typically one to three per chromosome pair. The mechanisms ensuring that most DSBs are repaired as non-COs and the evolutionary forces imposing this constraint are poorly understood. Here we identified Topoisomerase3α (TOP3α) and the RECQ4 helicases–the Arabidopsis slow growth suppressor 1 (Sgs1)/Bloom syndrome protein (BLM) homologs–as major barriers to meiotic CO formation. First, the characterization of a specific TOP3α mutant allele revealed that, in addition to its role in DNA repair, this topoisomerase antagonizes CO formation. Further, we found that RECQ4A and RECQ4B constitute the strongest meiotic anti-CO activity identified to date, their concomitant depletion leading to a sixfold increase in CO frequency. In both top3α and recq4ab mutants, DSB number is unaffected, and extra COs arise from a normally minor pathway. Finally, both TOP3α and RECQ4A/B act independently of the previously identified anti-CO Fanconi anemia of complementation group M (FANCM) helicase. This finding shows that several parallel pathways actively limit CO formation and suggests that the RECQA/B and FANCM helicases prevent COs by processing different substrates. Despite a ninefold increase in CO frequency, chromosome segregation was unaffected. This finding supports the idea that CO number is restricted not because of mechanical constraints but likely because of the long-term costs of recombination. Furthermore, this work demonstrates how manipulating a few genes holds great promise for increasing recombination frequency in plant-breeding programs.

Digital object identifier (DOI): 10.1073/pnas.1423107112