Estudo da origem e evolução dos cromossomos sexuais do gênero Megaleporinus a partir de sequências repetitivas
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Data
2019-02-28
Autores
Crepaldi, Carolina [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Cromossomos sexuais se apresentam como entidades dinâmicas dentro de um genoma, com evolução, morfologia e conteúdo genético únicos, e tendo evoluído de maneiras independentes dentro dos grupos de vertebrados. No caso dos peixes, apesar da maioria das espécies não apresentarem cromossomos sexuais diferenciados, existe uma enorme diversidade de mecanismos cromossômicos para a determinação do sexo, incluindo fêmeas ou machos heterogaméticos e sistemas simples ou múltiplos. Na maioria dos casos, a diferença entre os homólogos sexuais envolve blocos heterocromáticos, sendo bem estabelecidos em sistemas do tipo ZZ/ZW em que perda ou ganho de heterocromatina são as principais causas de diferenciação entre estes cromossomos. O gênero Megaleporinus, pertencente à família Anostomidae e com cromossomo heteromórfico W, é um modelo interessante para estudo da evolução e seleção desta heterogametia, especialmente pela alta quantidade de sequências repetitivas presente em seus cromossomos sexuais e a possível implicação na diferenciação destes. Assim, no presente trabalho, a análise feita de elementos repetitivos pelo RepeatExplorer na fêmea de Megaleporinus elongatus mostrou que esta possuiu 22.2% dos reads aleatórios de seu genoma constituídos por DNAs repetitivos, sendo 5.6% correspondentes a DNAs satélites. Foram isolados 69 variantes de DNAs satélites da fêmea, com tamanhos entre 20pb e 245pb, que foram caracterizados e validados experimentalmente. Por fim, estes foram mapeados através de hibridação in situ fluorescente nos cromossomos da espécie. Os 16 variantes de DNAs satélites com sinais conspícuo de hibridação estavam entre os mais abundantes do genoma e com exceção de 3, estes satélites clusterizados estavam presentes no cromossomo heteromórfico W. Apesar de poucos, em relação ao total isolado, estarem hibridados no cromossomo sexual, estes se mostram bem representativos e bem distribuídos no braço q do mesmo, denotando sua composição variada e acúmulo de repetições abundantes no seu pouco tempo de evolução. Estes mesmos DNAs satélites hibridados em M. elongatus foram mapeados em Megaleporinus macrocephalus, demonstrando a variável distribuição destes satélites quando comparando os cromossomos W das duas espécies, e em Leporinus friderici, onde a ausência de variantes clusterizados demonstra o acúmulo mais abundante e diferenciado nas espécies que possuem o cromossomo heteromórfico. Os dados obtidos fornecem mais informações sobre as características e a organização dos DNAs satélites do genoma da espécie de estudo, bem como auxilia a elucidar a distribuição e incidência deste tipo de sequências repetitivas no cromossomo sexual heteromórfico do gênero Megaleporinus.
Sex chromosomes are dynamic entities inside a genome, presenting unique evolution, morphology and genetic content and having evolved independently within vertebrates. In fish, although most species do not present differentiated sex chromosomes, there is an enormous diversity of chromosomic mechanisms for sexual determination that may include female or male heterogamety and simple or multiple sexual systems. In most cases, the difference between sexual homologues involve heterochromatic blocks and this fact is well established in species with the ZZ/ZW system, in which the gain or loss of heterochromatin is the main cause for chromosome differentiation. The genus Megaleporinus, from the Anostomidae family and with a ZZ/ZW sexual system, is an interesting model for studies of evolution and selection of sex chromosomes in fish, especially because the presence of heteromorphic sex chromosomes is restricted to just a few species of the genus and there is a high quantity of repetitive sequences in their chromosomes. In the present work, the analysis of Megaleporinus elongatus female genome repetitive content by RepeatExplorer returned 22.2% of its analysed reads constituted of repetitive DNA. From this, 5.6% correspondes to satellite DNA, and 69 satDNA variants were isolated and manually annotated, with sizes ranging from 20bp to 245bp, and validated through PCR. These variants were mapped through fluorescence in situ hybridisation on the species’ chromosomes. The 16 satellites that had conspicuous hybridisation signals were amongst the most abundant satellites in the female analysed genome reads, with exception of three of them. The signals on the W chromosome were distributed in a variable way throughout its q arm and although few variants were clustered, in comparison to the amount isolated through annotation, this chromosome’s composition shows a relevant diversity and accumulation of repetitive content in the fast evolution process of its sex system. These same satDNA variants were physically mapped in M. macrocephalus, which showed a diverse distribution in this species’ W chromosome in comparison to M. elongatus; and Leporinus friderici, where the absence of clustered satDNAs denotes the lack of abundant repetitions in this species and reiterates the high degree of satDNA accumulation on the Megaleporinus genus and its heteromorphic chromosome. The data obtained in this work offers more information about satDNA characteristics and organisation of the studied species, as well as helps clarify the distribution and incidence of these repetitive sequences in the heteromorphic sex chromosome throughout the genus as a whole.
Sex chromosomes are dynamic entities inside a genome, presenting unique evolution, morphology and genetic content and having evolved independently within vertebrates. In fish, although most species do not present differentiated sex chromosomes, there is an enormous diversity of chromosomic mechanisms for sexual determination that may include female or male heterogamety and simple or multiple sexual systems. In most cases, the difference between sexual homologues involve heterochromatic blocks and this fact is well established in species with the ZZ/ZW system, in which the gain or loss of heterochromatin is the main cause for chromosome differentiation. The genus Megaleporinus, from the Anostomidae family and with a ZZ/ZW sexual system, is an interesting model for studies of evolution and selection of sex chromosomes in fish, especially because the presence of heteromorphic sex chromosomes is restricted to just a few species of the genus and there is a high quantity of repetitive sequences in their chromosomes. In the present work, the analysis of Megaleporinus elongatus female genome repetitive content by RepeatExplorer returned 22.2% of its analysed reads constituted of repetitive DNA. From this, 5.6% correspondes to satellite DNA, and 69 satDNA variants were isolated and manually annotated, with sizes ranging from 20bp to 245bp, and validated through PCR. These variants were mapped through fluorescence in situ hybridisation on the species’ chromosomes. The 16 satellites that had conspicuous hybridisation signals were amongst the most abundant satellites in the female analysed genome reads, with exception of three of them. The signals on the W chromosome were distributed in a variable way throughout its q arm and although few variants were clustered, in comparison to the amount isolated through annotation, this chromosome’s composition shows a relevant diversity and accumulation of repetitive content in the fast evolution process of its sex system. These same satDNA variants were physically mapped in M. macrocephalus, which showed a diverse distribution in this species’ W chromosome in comparison to M. elongatus; and Leporinus friderici, where the absence of clustered satDNAs denotes the lack of abundant repetitions in this species and reiterates the high degree of satDNA accumulation on the Megaleporinus genus and its heteromorphic chromosome. The data obtained in this work offers more information about satDNA characteristics and organisation of the studied species, as well as helps clarify the distribution and incidence of these repetitive sequences in the heteromorphic sex chromosome throughout the genus as a whole.
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Palavras-chave
Cromossomo sexual, Conteúdo DNAs repetitivos, Satelitoma, FISH, Characiformes, Sex chromosome, Repetitive DNA content, Satellitome