Molecular composition and evolution of b chromosomes in neotropical grasshoppers: a cytogenomic approach
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2021-12-08
Autores
Milani, Diogo [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Cromossomos supranumerários ou Bs são elementos dispensáveis adicionais que estão presentes em alguns indivíduos em uma determinada população de uma determinada espécie. Até agora, estima-se que estejam presentes em mais de 15% dos eucariotos, incluindo plantas, fungos e animais. Uma das principais características dos Bs é que eles não se recombinam com o complemento A, evoluindo independentemente do resto do genoma. Eles também podem se acumular ao longo de gerações por forças evolutivas ainda não muito conhecidas como resultado de impulsos por distorção do padrão normal de herança de Mendel. Uma característica muito comum dos cromossomos B é sua heterocromatinização e acúmulo de DNAs repetitivos, responsáveis por sua evolução e diferenciação em relação ao complemento A. Genes funcionais associados principalmente à divisão e regulação cromossômica também foram documentados. Apesar dos ortópteros apresentarem grande número de espécies portando cromossomos B, estudos com abordagens recentes usando a integração entre sequenciamento genômico e mapeamento cromossômico físico para melhor entendimento sobre origem, composição, evolução e comportamento estão concentrados principalmente em algumas espécies. Aqui, nosso objetivo foi elucidar a composição molecular e possível ancestralidade dos cromossomos B em diferentes gafanhotos neotropicais, com uma extensão para entender a dinâmica populacional do cromossomo B de Abracris flavolineata. O presente trabalho teve basicamente três etapas principais apresentadas em três manuscritos. No primeiro, por análise de satDNAs, fornecemos suporte para a origem intraespecífica do cromossomo B de Rhammatocerus brasiliensis, Schistocerca rubiginosa e Xyleus discoideus angulatus, a partir de cromossomos pequenos, o que parece ser uma característica comum para este grupo. O segundo capítulo apresentou o cromossomo B eucromático incomum de A. flavolineata que diferentemente a outros Bs poderia ser um elemento jovem, não enriquecido com DNA repetitivo, mostrando padrão C-negativo e alta semelhança com o complemento A. Esses resultados obtidos por sequenciamento genômico, bioinformática e mapeamento cromossômico, sugerem uma origem intraespecífica do cromossomo B a partir do par L1, provavelmente passando por misdivisão e formação de isocromossomo. Finalmente, no terceiro capítulo, mais dois Bs foram encontrados em populações de A. flavolineata com frequências diferente e composição altamente diferenciada. As evidências obtidas pela análise do repeatoma reforçaram que os Bs são jovens, mas em diferentes estágios de heterocromatinização, principalmente devido à intensa amplificação de repetições de satDNA, como observado para o B da população da Argentina. A variante do B da população de Cabo/PE apresentou mais semelhança com a variante de Rio Claro/SP do que a de Posadas/ARG. Além disso, a origem única das variantes de Bs das populações de A. flavolineata é discutida.
Supernumerary chromosomes or Bs are additional dispensable elements that are present in some individuals in a given population of a given species. So far, they were estimated to be present in more than 15% of eukaryotes, including plants, fungi and animals. One of the main characteristics of Bs is that they do not recombine with the A complement, evolving independently of the rest of the genome. They also can accumulate along generations by not well-known evolutionary forces as results of drive by distortion of the normal Mendelian inheritance pattern. A very common feature for the B chromosomes is their heterochromatinization and accumulation of repetitive DNAs, which account for its evolution and differentiation in comparison to A complement. Functional genes mainly associated with division and chromosome regulation were also documented. Despite orthopterans present large number of species harboring B chromosomes, studies with recent approaches using the integration between genomic sequencing and physical chromosome mapping for better understanding about origin, composition, evolution and behavior are concentrated primarily on a few species. Here, our goal was to elucidate the molecular composition and possible ancestry of B chromosomes in different Neotropical grasshoppers, with an extension to understand the populational dynamics of the B chromosome of Abracris flavolineata. The present work had basically three main steps presented in three manuscripts. The first one, by satDNAs analysis, we provided support for intraspecific origin of the B chromosome of Rhammatocerus brasiliensis, Schistocerca rubiginosa and Xyleus discoideus angulatus, from small chromosomes, which appears to be a common feature for this group. The second chapter presented the uncommon euchromatic B chromosome of A. flavolineata that differentially to other Bs could be a young element, not enriched with repetitive DNA, showing Cnegative pattern and high resemblance with the A complement. These results obtained by genomic sequencing, bioinformatics and chromosome mapping, suggests an intraspecific origin of the B chromosome from L1 pair, probably passing through misdivision and isochromosome formation. Finally, in the third chapter two more Bs were found on A. flavolineata populations with different frequency and highly differentiated in composition. The evidences gathered by repeatome analysis reinforced that the Bs are young but in different stages of heterochromatinization, mainly due to intense amplification of satDNA repeats, as for the B from Argentina population. The B variant from Cabo/PE population presented more resemblance to the variant from Rio Claro/SP than to from Posadas/ARG. Moreover, the unique origin of the B variants of A. flavolineata populations is discussed.
Supernumerary chromosomes or Bs are additional dispensable elements that are present in some individuals in a given population of a given species. So far, they were estimated to be present in more than 15% of eukaryotes, including plants, fungi and animals. One of the main characteristics of Bs is that they do not recombine with the A complement, evolving independently of the rest of the genome. They also can accumulate along generations by not well-known evolutionary forces as results of drive by distortion of the normal Mendelian inheritance pattern. A very common feature for the B chromosomes is their heterochromatinization and accumulation of repetitive DNAs, which account for its evolution and differentiation in comparison to A complement. Functional genes mainly associated with division and chromosome regulation were also documented. Despite orthopterans present large number of species harboring B chromosomes, studies with recent approaches using the integration between genomic sequencing and physical chromosome mapping for better understanding about origin, composition, evolution and behavior are concentrated primarily on a few species. Here, our goal was to elucidate the molecular composition and possible ancestry of B chromosomes in different Neotropical grasshoppers, with an extension to understand the populational dynamics of the B chromosome of Abracris flavolineata. The present work had basically three main steps presented in three manuscripts. The first one, by satDNAs analysis, we provided support for intraspecific origin of the B chromosome of Rhammatocerus brasiliensis, Schistocerca rubiginosa and Xyleus discoideus angulatus, from small chromosomes, which appears to be a common feature for this group. The second chapter presented the uncommon euchromatic B chromosome of A. flavolineata that differentially to other Bs could be a young element, not enriched with repetitive DNA, showing Cnegative pattern and high resemblance with the A complement. These results obtained by genomic sequencing, bioinformatics and chromosome mapping, suggests an intraspecific origin of the B chromosome from L1 pair, probably passing through misdivision and isochromosome formation. Finally, in the third chapter two more Bs were found on A. flavolineata populations with different frequency and highly differentiated in composition. The evidences gathered by repeatome analysis reinforced that the Bs are young but in different stages of heterochromatinization, mainly due to intense amplification of satDNA repeats, as for the B from Argentina population. The B variant from Cabo/PE population presented more resemblance to the variant from Rio Claro/SP than to from Posadas/ARG. Moreover, the unique origin of the B variants of A. flavolineata populations is discussed.
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Palavras-chave
Cromossomos supranumerários, DNA repetitivo, FISH, Sequenciamento de DNA, População, Supernumerary chromosomes, Repetitive DNA, DNA sequencing, Population