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Vicari MR, Bruschi DP, Cabral-de-Mello DC, Nogaroto V. Telomere organization and the interstitial telomeric sites involvement in insects and vertebrates chromosome evolution. Genet Mol Biol 2022; 45:e20220071. [DOI: 10.1590/1678-4685-gmb-2022-0071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 09/24/2022] [Indexed: 11/16/2022] Open
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García E, Cross I, Portela-Bens S, Rodríguez ME, García-Angulo A, Molina B, Cuadrado A, Liehr T, Rebordinos L. Integrative genetic map of repetitive DNA in the sole Solea senegalensis genome shows a Rex transposon located in a proto-sex chromosome. Sci Rep 2019; 9:17146. [PMID: 31748593 PMCID: PMC6868151 DOI: 10.1038/s41598-019-53673-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 11/05/2019] [Indexed: 01/07/2023] Open
Abstract
Repetitive sequences play an essential role in the structural and functional evolution of the genome, particularly in the sexual chromosomes. The Senegalese sole (Solea senegalensis) is a valuable flatfish in aquaculture albeit few studies have addressed the mapping and characterization of repetitive DNA families. Here we analyzed the Simple Sequence Repeats (SSRs) and Transposable elements (TEs) content from fifty-seven BAC clones (spanning 7.9 Mb) of this species, located in chromosomes by multiple fluorescence in situ hybridization (m-BAC-FISH) technique. The SSR analysis revealed an average density of 675.1 loci per Mb and a high abundance (59.69%) of dinucleotide coverage was observed, being ‘AC’ the most abundant. An SSR-FISH analysis using eleven probes was also carried out and seven of the 11 probes yielded positive signals. ‘AC’ probes were present as large clusters in almost all chromosomes, supporting the bioinformatic analysis. Regarding TEs, DNA transposons (Class II) were the most abundant. In Class I, LINE elements were the most abundant and the hAT family was the most represented in Class II. Rex/Babar subfamily, observed in two BAC clones mapping to chromosome pair 1, showed the longest match. This chromosome pair has been recently reported as a putative sexual proto-chromosome in this species, highlighting the possible role of the Rex element in the evolution of this chromosome. In the Rex1 phylogenetic tree, the Senegalese sole Rex1 retrotransposon could be associated with one of the four major ancient lineages in fish genomes, in which it is included O. latipes.
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Affiliation(s)
- Emilio García
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain
| | - Ismael Cross
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain
| | - Silvia Portela-Bens
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain
| | - María E Rodríguez
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain
| | - Aglaya García-Angulo
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain
| | - Belén Molina
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain
| | - Angeles Cuadrado
- Department of Biomedicine and Biotechnology, University of Alcala, 28871, Alcalá de Henares (Madrid), Spain
| | - Thomas Liehr
- Institut für Humangenetik, Universitätsklinikum Jena, 07747, Jena, Germany
| | - Laureana Rebordinos
- Área de Genética, Facultad de Ciencias del Mar y Ambientales, INMAR, Universidad de Cádiz, 11510, Cádiz, Spain.
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Gammerdinger WJ, Kocher TD. Unusual Diversity of Sex Chromosomes in African Cichlid Fishes. Genes (Basel) 2018; 9:E480. [PMID: 30287777 PMCID: PMC6210639 DOI: 10.3390/genes9100480] [Citation(s) in RCA: 76] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 09/26/2018] [Accepted: 10/01/2018] [Indexed: 11/30/2022] Open
Abstract
African cichlids display a remarkable assortment of jaw morphologies, pigmentation patterns, and mating behaviors. In addition to this previously documented diversity, recent studies have documented a rich diversity of sex chromosomes within these fishes. Here we review the known sex-determination network within vertebrates, and the extraordinary number of sex chromosomes systems segregating in African cichlids. We also propose a model for understanding the unusual number of sex chromosome systems within this clade.
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Affiliation(s)
- William J Gammerdinger
- Institute of Science and Technology (IST) Austria, Am Campus 1, 3400 Klosterneuburg, Austria.
| | - Thomas D Kocher
- Department of Biology, University of Maryland, College Park, MD 20742, USA.
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A syntenic region conserved from fish to Mammalian x chromosome. INTERNATIONAL JOURNAL OF EVOLUTIONARY BIOLOGY 2014; 2014:873935. [PMID: 25506037 PMCID: PMC4254068 DOI: 10.1155/2014/873935] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 10/30/2014] [Accepted: 11/02/2014] [Indexed: 11/29/2022]
Abstract
Sex chromosomes bearing the sex-determining gene initiate development along the male or female pathway, no matter which sex is determined by XY male or ZW female heterogamety. Sex chromosomes originate from ancient autosomes but evolved rapidly after the acquisition of sex-determining factors which are highly divergent between species. In the heterogametic male system (XY system), the X chromosome is relatively evolutionary silent and maintains most of its ancestral genes, in contrast to its Y counterpart that has evolved rapidly and degenerated. Sex in a teleost fish, the Nile tilapia (Oreochromis niloticus), is determined genetically via an XY system, in which an unpaired region is present in the largest chromosome pair. We defined the differences in DNA contents present in this chromosome with a two-color comparative genomic hybridization (CGH) and the random amplified polymorphic DNA (RAPD) approach in XY males. We further identified a syntenic segment within this region that is well conserved in several teleosts. Through comparative genome analysis, this syntenic segment was also shown to be present in mammalian X chromosomes, suggesting a common ancestral origin of vertebrate sex chromosomes.
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Liu F, Sun F, Li J, Xia JH, Lin G, Tu RJ, Yue GH. A microsatellite-based linkage map of salt tolerant tilapia (Oreochromis mossambicus x Oreochromis spp.) and mapping of sex-determining loci. BMC Genomics 2013; 14:58. [PMID: 23356773 PMCID: PMC3565888 DOI: 10.1186/1471-2164-14-58] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 01/22/2013] [Indexed: 11/16/2022] Open
Abstract
Background Tilapia is the common name for a group of cichlid fishes and is one of the most important aquacultured freshwater food fish. Mozambique tilapia and its hybrids, including red tilapia are main representatives of salt tolerant tilapias. A linkage map is an essential framework for mapping QTL for important traits, positional cloning of genes and understanding of genome evolution. Results We constructed a consensus linkage map of Mozambique tilapia and red tilapia using 95 individuals from two F1 families and 401 microsatellites including 282 EST-derived markers. In addition, we conducted comparative mapping and searched for sex-determining loci on the whole genome. These 401 microsatellites were assigned to 22 linkage groups. The map spanned 1067.6 cM with an average inter-marker distance of 3.3 cM. Comparative mapping between tilapia and stickleback, medaka, pufferfish and zebrafish revealed clear homologous relationships between chromosomes from different species. We found evidence for the fusion of two sets of two independent chromosomes forming two new chromosome pairs, leading to a reduction of 24 chromosome pairs in their ancestor to 22 pairs in tilapias. The XY sex determination locus in Mozambique tilapia was mapped on LG1, and verified in five families containing 549 individuals. The major XY sex determination locus in red tilapia was located on LG22, and verified in two families containing 275 individuals. Conclusions A first-generation linkage map of salt tolerant tilapia was constructed using 401 microsatellites. Two separate fusions of two sets of two independent chromosomes may lead to a reduction of 24 chromosome pairs in their ancestor to 22 pairs in tilapias. The XY sex-determining loci from Mozambique tilapia and red tilapia were mapped on LG1 and LG22, respectively. This map provides a useful resource for QTL mapping for important traits and comparative genome studies. The DNA markers linked to the sex-determining loci could be used in the selection of YY males for breeding all-male populations of salt tolerant tilapia, as well as in studies on mechanisms of sex determination in fish.
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Affiliation(s)
- Feng Liu
- Molecular Population Genetics Group, Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore, 117604, Republic of Singapore
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Cnaani A. The Tilapias' Chromosomes Influencing Sex Determination. Cytogenet Genome Res 2013; 141:195-205. [DOI: 10.1159/000355304] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Mazzuchelli J, Kocher TD, Yang F, Martins C. Integrating cytogenetics and genomics in comparative evolutionary studies of cichlid fish. BMC Genomics 2012; 13:463. [PMID: 22958299 PMCID: PMC3463429 DOI: 10.1186/1471-2164-13-463] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Accepted: 08/09/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The availability of a large number of recently sequenced vertebrate genomes opens new avenues to integrate cytogenetics and genomics in comparative and evolutionary studies. Cytogenetic mapping can offer alternative means to identify conserved synteny shared by distinct genomes and also to define genome regions that are still not fine characterized even after wide-ranging nucleotide sequence efforts. An efficient way to perform comparative cytogenetic mapping is based on BAC clones mapping by fluorescence in situ hybridization. In this report, to address the knowledge gap on the genome evolution in cichlid fishes, BAC clones of an Oreochromis niloticus library covering the linkage groups (LG) 1, 3, 5, and 7 were mapped onto the chromosomes of 9 African cichlid species. The cytogenetic mapping data were also integrated with BAC-end sequences information of O. niloticus and comparatively analyzed against the genome of other fish species and vertebrates. RESULTS The location of BACs from LG1, 3, 5, and 7 revealed a strong chromosomal conservation among the analyzed cichlid species genomes, which evidenced a synteny of the markers of each LG. Comparative in silico analysis also identified large genomic blocks that were conserved in distantly related fish groups and also in other vertebrates. CONCLUSIONS Although it has been suggested that fishes contain plastic genomes with high rates of chromosomal rearrangements and probably low rates of synteny conservation, our results evidence that large syntenic chromosome segments have been maintained conserved during evolution, at least for the considered markers. Additionally, our current cytogenetic mapping efforts integrated with genomic approaches conduct to a new perspective to address important questions involving chromosome evolution in fishes.
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Affiliation(s)
- Juliana Mazzuchelli
- Department of Morphology, Bioscience Institute, UNESP - São Paulo State University, 18618-970, Botucatu, SP, Brazil
| | | | - Fengtang Yang
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK
| | - Cesar Martins
- Department of Morphology, Bioscience Institute, UNESP - São Paulo State University, 18618-970, Botucatu, SP, Brazil
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Abstract
On August 31, 2011 at the 18th International Chromosome Conference in Manchester, Jenny Graves took on Jenn Hughes to debate the demise (or otherwise) of the mammalian Y chromosome. Sex chromosome evolution is an example of convergence; there are numerous examples of XY and ZW systems with varying degrees of differentiation and isolated examples of the Y disappearing in some lineages. It is agreed that the Y was once genetically identical to its partner and that the present-day human sex chromosomes retain only traces of their shared ancestry. The euchromatic portion of the male-specific region of the Y is ~1/6 of the size of the X and has only ~1/12 the number of genes. The big question however is whether this degradation will continue or whether it has reached a point of equilibrium. Jenny Graves argued that the Y chromosome is subject to higher rates of variation and inefficient selection and that Ys (and Ws) degrade inexorably. She argued that there is evidence that the Y in other mammals has undergone lineage-specific degradation and already disappeared in some rodent lineages. She also pointed out that there is practically nothing left of the original human Y and the added part of the human Y is degrading rapidly. Jenn Hughes on the other hand argued that the Y has not disappeared yet and it has been around for hundreds of millions of years. She stated that it has shown that it can outsmart genetic decay in the absence of "normal" recombination and that most of its genes on the human Y exhibit signs of purifying selection. She noted that it has added at least eight different genes, many of which have subsequently expanded in copy number, and that it has not lost any genes since the human and chimpanzee diverged ~6 million years ago. The issue was put to the vote with an exact 50/50 split among the opinion of the audience; an interesting (though perhaps not entirely unexpected) skew however was noted in the sex ratio of those for and against the notion.
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Ferreira DC, Porto-Foresti F, Oliveira C, Foresti F. Transposable elements as a potential source for understanding the fish genome. Mob Genet Elements 2011; 1:112-117. [PMID: 22016858 DOI: 10.4161/mge.1.2.16731] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2011] [Revised: 05/11/2011] [Accepted: 05/30/2011] [Indexed: 12/24/2022] Open
Abstract
Transposable elements are repetitive sequences with the capacity tomove inside of the genome. They constitute the majority of the eukaryotic genomes, and are extensively present in the human genome, representing more than 45% of the genome sequences. The knowledge of the origin and function of these elements in the fish genome is still reduced and fragmented, mainly with regard to its structure and organization in the chromosomes of the representatives of this biological group, with data currently available for very few species that represent the great variety of forms and existing diversity. Comparative analyses ascertain differences in the organization of such elements in the species studied up to the present. They can be part of the heterochromatic regions in some species or be spread throughout the genome in others. The main objective of the present revision is to discuss the aspects of the organization of transposable elements in the fish genome.
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Affiliation(s)
- Daniela Cristina Ferreira
- Departamento de Morfologia; Instituto de Biociência; Universidade Estadual Paulista; Bauru, SP Brazil
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Characterisation of the chromosome fusions in Oreochromis karongae. Chromosome Res 2010; 18:575-86. [PMID: 20574823 DOI: 10.1007/s10577-010-9141-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Revised: 06/03/2010] [Accepted: 06/04/2010] [Indexed: 10/19/2022]
Abstract
Oreochromis karongae, one of the "chambo" tilapia species from Lake Malawi, has a karyotype of 2n = 38, making it one of the few species investigated to differ from the typical tilapia karyotype (2n = 44). The O. karongae karyotype consists of one large subtelocentric pair of chromosomes, four medium-sized pairs (three subtelocentric and one submetacentric) and 14 small pairs. The five largest pairs could be distinguished from each other on the basis of size, morphology and a series of fluorescence in situ hybridisation (FISH) probes. The largest pair is easily distinguished on the basis of size and a chromosome 1 (linkage group 3) bacterial artificial chromosome (BAC) FISH probe from Oreochromis niloticus. BAC clones from O. niloticus chromosome 2 (linkage group 7) hybridised to one of the medium-sized subtelocentric chromosome pairs (no. 5) of O. karongae, distinguishing the ancestral medium-sized pair from the three other medium-sized chromosome pairs (nos. 2, 3 and 4) that appear to have resulted from fusions. SATA repetitive DNA hybridised to the centromeres of all 19 chromosome pairs and also revealed the locations of the relic centromeres in the three fused pairs. Telomeric (TTAGGG)(n) repeats were identified in the telomeres of all chromosomes, and an interstitial telomeric site (ITS) was identified in three chromosomal pairs (no. 2, 3 and 4). Additionally, two ITS sites were identified in the largest chromosome pair (pair 1), confirming the origin of this chromosome from three ancestral chromosomes. SATA and ITS sites allowed the orientation of the fusions in pairs 2, 3 and 4, which all appear to have been in different orientations (q-q, p-q and p-p, respectively). One of these fusions (O. karongae chromosome pair no. 2) involves a small chromosome (equivalent to linkage group 1), which in O. niloticus carries the main sex-determining gene. 4',6-Diamidino-2-phenyloindole staining of the synaptonemal complex in male O. karongae revealed the presumptive positions of the kinetochores, which correspond well to the centromeric positions observed in the mitotic karyotype.
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12
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Poletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet 2010; 11:50. [PMID: 20550671 PMCID: PMC2896337 DOI: 10.1186/1471-2156-11-50] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2010] [Accepted: 06/15/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Cichlid fishes have been the subject of increasing scientific interest because of their rapid adaptive radiation which has led to an extensive ecological diversity and their enormous importance to tropical and subtropical aquaculture. To increase our understanding of chromosome evolution among cichlid species, karyotypes of one Asian, 22 African, and 30 South American cichlid species were investigated, and chromosomal data of the family was reviewed. RESULTS Although there is extensive variation in the karyotypes of cichlid fishes (from 2n = 32 to 2n = 60 chromosomes), the modal chromosome number for South American species was 2n = 48 and the modal number for the African ones was 2n = 44. The only Asian species analyzed, Etroplus maculatus, was observed to have 46 chromosomes. The presence of one or two macro B chromosomes was detected in two African species. The cytogenetic mapping of 18S ribosomal RNA (18S rRNA) gene revealed a variable number of clusters among species varying from two to six. CONCLUSIONS The karyotype diversification of cichlids seems to have occurred through several chromosomal rearrangements involving fissions, fusions and inversions. It was possible to identify karyotype markers for the subfamilies Pseudocrenilabrinae (African) and Cichlinae (American). The karyotype analyses did not clarify the phylogenetic relationship among the Cichlinae tribes. On the other hand, the two major groups of Pseudocrenilabrinae (tilapiine and haplochromine) were clearly discriminated based on the characteristics of their karyotypes. The cytogenetic mapping of 18S ribosomal RNA (18S rRNA) gene did not follow the chromosome diversification in the family. The dynamic evolution of the repeated units of rRNA genes generates patterns of chromosomal distribution that do not help follows the phylogenetic relationships among taxa. The presence of B chromosomes in cichlids is of particular interest because they may not be represented in the reference genome sequences currently being obtained.
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Affiliation(s)
- Andréia B Poletto
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
| | - Irani A Ferreira
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
| | - Diogo C Cabral-de-Mello
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
| | - Rafael T Nakajima
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
| | - Juliana Mazzuchelli
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
| | - Heraldo B Ribeiro
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
| | - Paulo C Venere
- UFMT - Universidade Federal de Mato Grosso, Instituto Universitário do Araguaia, Pontal do Araguaia, MT, Brazil
| | - Mauro Nirchio
- Universidad de Oriente, Escuela de Ciencias Aplicadas del Mar, Boca de Rio, Venezuela
| | - Thomas D Kocher
- University of Maryland, Department of Biology, College Park, MD 20742 USA
| | - Cesar Martins
- UNESP - Universidade Estadual Paulista, Instituto de Biociências, Departamento de Morfologia, Botucatu, SP, Brazil
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Targino Valente G, Henrique Schneider C, Claudia Gross M, Feldberg E, Martins C. Comparative cytogenetics of cichlid fishes through genomic in-situ hybridization (GISH) with emphasis on Oreochromis niloticus. Chromosome Res 2009; 17:791-9. [PMID: 19685270 DOI: 10.1007/s10577-009-9067-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2009] [Accepted: 07/27/2009] [Indexed: 10/20/2022]
Abstract
Cichlidae is the most species-rich freshwater family of Perciformes and has attracted the attention of aquarium hobbyists, aquaculturists, and sport fisherman. Oreochromis niloticus is very important in aquaculture today and is currently used in varied areas of study as an 'experimental model'. Oreochromis niloticus has been characterized using classical and molecular cytogenetic techniques, with special attention paid to heterochromatin structure and the identification of sex chromosomes. In this study, we compare the genome of O. niloticus with that of other cichlids from Africa and South America using genomic in-situ hybridization (GISH). Our results show that at least some elements comprising the pericentromeric heterochromatin of Nile tilapia are species-specific and that the sequence of the majority of the long arm of the largest chromosome pair is conserved within the tilapiine group, which is composed of the genera Tilapia, Oreochromis, and Sarotherodon. It is suggested that the extensive regions of repeated DNA in the largest chromosome pair of O. niloticus resulted from chromosome rearrangement or accumulation caused by recombination suppression during the evolutionary history of the tilapiines.
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Affiliation(s)
- Guilherme Targino Valente
- Laboratório de Genômica Integrativa, Departamento de Morfologia, Instituto de Biociências, UNESP - Universidade Estadual Paulista, Botucatu, SP, Brazil
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Brinn MNA, Porto JIR, Feldberg E. Karyological evidence for interspecific hybridization between Cichla monoculus and C. temensis (Perciformes, Cichlidae) in the Amazon. Hereditas 2006; 141:252-7. [PMID: 15703041 DOI: 10.1111/j.1601-5223.2004.01830.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Cichla monoculus, Cichla temensis (peacock bass or tucunare), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatuma (C. monoculus, C. temensis and their natural hybrid), Jau (C. temensis), and Solimoes rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n=48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla.
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Ezaz T, Quinn AE, Miura I, Sarre SD, Georges A, Marshall Graves JA. The dragon lizard Pogona vitticeps has ZZ/ZW micro-sex chromosomes. Chromosome Res 2005; 13:763-76. [PMID: 16331408 DOI: 10.1007/s10577-005-1010-9] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2005] [Accepted: 09/28/2005] [Indexed: 10/25/2022]
Abstract
The bearded dragon, Pogona vitticeps (Agamidae: Reptilia) is an agamid lizard endemic to Australia. Like crocodilians and many turtles, temperature-dependent sex determination (TSD) is common in agamid lizards, although many species have genotypic sex determination (GSD). P. vitticeps is reported to have GSD, but no detectable sex chromosomes. Here we used molecular cytogenetic and differential banding techniques to reveal sex chromosomes in this species. Comparative genomic hybridization (CGH), GTG- and C-banding identified a highly heterochromatic microchromosome specific to females, demonstrating female heterogamety (ZZ/ZW) in this species. We isolated the P. vitticeps W chromosome by microdissection, re-amplified the DNA and used it to paint the W. No unpaired bivalents were detected in male synaptonemal complexes at meiotic pachytene, confirming male homogamety. We conclude that P. vitticeps has differentiated previously unidentifable W and Z micro-sex chromosomes, the first to be demonstrated in an agamid lizard. Our finding implies that heterochromatinization of the heterogametic chromosome occurred during sex chromosome differentiation in this species, as is the case in some lizards and many snakes, as well as in birds and mammals. Many GSD reptiles with cryptic sex chromosomes may also prove to have micro-sex chromosomes. Reptile microchromosomes, long dismissed as non-functional minutiae and often omitted from karyotypes, therefore deserve closer scrutiny with new and more sensitive techniques.
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Affiliation(s)
- Tariq Ezaz
- Comparative Genomics Group, Research School of Biological Sciences, The Australian National University, Canberra.
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