História evolutiva e divergência funcional do gene de especiação OdsH e sua duplicata unc-4 em Drosophilidae
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2022-07-08
Autores
Nunes, William Vilas Boas
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Universidade Estadual Paulista (Unesp)
Resumo
O gene Odyssesus (OdsH) foi o primeiro gene de especiação descrito em Drosophila, assim caracterizado em face de sua associação com a esterilidade híbrida entre Drosophila simulans e Drosophila mauritiana. Sua origem é atribuída à duplicação do gene unc-4, o qual é muito conservado em metazoários e relacionado a funções neurais. Tanto OdsH como unc-4 codificam homeodomínios e atuam como fatores de transcrição. A ocorrência dessa duplicação foi circunscrita ao subgênero Sophophora, contudo, análises preliminares indicaram sua ocorrência em outros subgêneros de Drosophila. O presente estudo teve como objetivo ampliar a busca pelo gene OdsH para além do gênero Drosophila, de modo definir a extensão de sua ocorrência e datar o evento da duplicação, bem como, caracterizar a evolução molecular e funcional desta duplicata. Foram encontradas evidências da ocorrência de OdsH nos genomas de espécies das duas tribos da subfamília Drosophilinae (Drosophilini e Colocasiomyini) da família Drosophilidae, mas não em genomas da subfamília Steganinae. A Inferência Bayesiana utilizada para coestimar as relações filogenéticas e o tempo de divergência entre as sequências das duplicatas unc-4 e OdsH indicaram que elas formam dois clados monofiléticos irmãos em Drosophilinae. Concordantemente com as estimativas de divergência das duas subfamílias, a datação da duplicação permitiu estimar sua origem há 55,58 milhões de anos atrás. As taxas de evolução desses genes indicaram assimetria, com aceleração da evolução de OdsH, sugerindo-se maior diversificação dessa duplicata anteriormente à divergência da subfamília Drosophilinae. Busca em bancos públicos de dados por transcriptomas de órgãos reprodutivos e não reprodutivos em espécies da subfamília Drosophilinae, confirmaram expressão inovativa de OdsH em testículos de Drosophila, o que não foi observado para unc-4. Adicionalmente, foi inferida a regulação de OdsH por fatores de transcrição relacionados à reprodução masculina. Análises dos domínios funcionais proteicos indicaram que a proteína OdsH apresenta maior divergência dos motivos funcionais, do homeodomínio e do octapeptídeo, do que Unc-4, e que a divergência observada no homeodomínio pode perturbar a energia de ligação ao DNA, tornando o sistema mais instável. Essas características permitem sugerir que as duas proteínas têm diferentes alvos de ligação na regulação de genes alvo. A proteína OdsH de D. mauritiana apresenta singularidades que podem estar associadas à sua incompatibilidade em relação ao genoma de D. simulans, e relacionada à esterilidade híbrida reportada entre as duas espécies. Os níveis de expressão de OdsH variam entre as espécies D. mojavensis e D. arizonae, e entre os híbridos férteis e estéreis, o que pode configurar um cenário de envolvimento de OdsH com a esterilidade híbrida. A expressão de OdsH nessas espécies ocorre nos espermatócitos, indicando que possivelmente desempenha a regulação de fatores meióticos e pós meióticos. Neste estudo reportamos de forma inédita que o gene OdsH teve origem no ancestral Drosophilinae e que reúne características que permitem propor sua neofuncionalização em funções sexuais masculinas logo após sua origem.
The Odysseus (OdsH) gene was the first speciation gene described in Drosophila, associated with hybrid sterility between Drosophila simulans and Drosophila mauritiana. Its origin is attributed to the duplication of unc-4, a gene highly conserved in metazoans and related to neural functions. Both OdsH and unc-4 are transcription factors that encode homeodomains. The occurrence of this duplication has been limited to the subgenus Sophophora, however preliminary analyses indicated its occurrence in other Drosophila subgenera. This study had the goal to expand the search for the OdsH beyond Drosophila genus, in order to define the extent of its occurrence and to date the duplication event, as well as to characterize the molecular and functional evolution of this duplicate. Evidence of the occurrence of OdsH was found in the genomes of species from two tribes of the Drosophilinae subfamily (Drosophilini and Colocasiomyini) of the Drosophilidae family, but not in genomes from the Steganinae subfamily. The Bayesian Inference used to co-estimate the phylogenetic relationships and the divergence time between sequences of the unc-4 and OdsH duplicates indicated that they form two monophyletic sister clades in Drosophilinae. In agreement with the divergence estimations of the two subfamilies, the duplication dating allowed us to estimate its origin at 55.58 million years ago. The evolutionary rates of these genes indicated asymmetry, with acceleration of OdsH evolution, suggesting greater diversification of this gene prior to the divergence of the Drosophilinae subfamily. Through expression level comparisons of reproductive and non-reproductive organs in species of the Drosophilinae subfamily, as well as data obtained via quantitative expression analysis specifically for D. mojavensis, D arizonae and their fertile and sterile hybrids, we have confirmed the innovative expression of OdsH in testes of Drosophila, which was not observed for unc-4. Additionally, we have found evidence of OdsH regulation by transcription factors related to male reproduction. Functional analysis of the protein domains indicated that the OdsH protein shows greater divergence of the functional motifs, as well as the homeodomain and the octapeptide, in comparison to Unc-4. Furthermore, the divergence observed in the homeodomain can disturb the DNA binding energy, making the system more unstable. These characteristics allow us to suggest that the two proteins have different binding targets in the regulation of target genes. The protein OdsH of D. mauritiana have specific features that may be associated with their incompatibility with the genome of D. simulans, as well as to the reported hybrid sterility. OdsH expression levels vary between D. mojavensis and D. arizonae species, and between fertile and sterile hybrids, which can configure a scenario of OdsH relationship with hybrid sterility. The expression of OdsH in these species occurs in spermatocytes, indicating that it possibly plays a role in the regulation of meiotic and post-meiotic factors. In this study, we reported an unprecedented way that the OdsH gene originated in the Drosophilinae ancestor. We also found that it has characteristics allowing us to propose its neofunctionalization in male sexual functions rapidly after its origin.
The Odysseus (OdsH) gene was the first speciation gene described in Drosophila, associated with hybrid sterility between Drosophila simulans and Drosophila mauritiana. Its origin is attributed to the duplication of unc-4, a gene highly conserved in metazoans and related to neural functions. Both OdsH and unc-4 are transcription factors that encode homeodomains. The occurrence of this duplication has been limited to the subgenus Sophophora, however preliminary analyses indicated its occurrence in other Drosophila subgenera. This study had the goal to expand the search for the OdsH beyond Drosophila genus, in order to define the extent of its occurrence and to date the duplication event, as well as to characterize the molecular and functional evolution of this duplicate. Evidence of the occurrence of OdsH was found in the genomes of species from two tribes of the Drosophilinae subfamily (Drosophilini and Colocasiomyini) of the Drosophilidae family, but not in genomes from the Steganinae subfamily. The Bayesian Inference used to co-estimate the phylogenetic relationships and the divergence time between sequences of the unc-4 and OdsH duplicates indicated that they form two monophyletic sister clades in Drosophilinae. In agreement with the divergence estimations of the two subfamilies, the duplication dating allowed us to estimate its origin at 55.58 million years ago. The evolutionary rates of these genes indicated asymmetry, with acceleration of OdsH evolution, suggesting greater diversification of this gene prior to the divergence of the Drosophilinae subfamily. Through expression level comparisons of reproductive and non-reproductive organs in species of the Drosophilinae subfamily, as well as data obtained via quantitative expression analysis specifically for D. mojavensis, D arizonae and their fertile and sterile hybrids, we have confirmed the innovative expression of OdsH in testes of Drosophila, which was not observed for unc-4. Additionally, we have found evidence of OdsH regulation by transcription factors related to male reproduction. Functional analysis of the protein domains indicated that the OdsH protein shows greater divergence of the functional motifs, as well as the homeodomain and the octapeptide, in comparison to Unc-4. Furthermore, the divergence observed in the homeodomain can disturb the DNA binding energy, making the system more unstable. These characteristics allow us to suggest that the two proteins have different binding targets in the regulation of target genes. The protein OdsH of D. mauritiana have specific features that may be associated with their incompatibility with the genome of D. simulans, as well as to the reported hybrid sterility. OdsH expression levels vary between D. mojavensis and D. arizonae species, and between fertile and sterile hybrids, which can configure a scenario of OdsH relationship with hybrid sterility. The expression of OdsH in these species occurs in spermatocytes, indicating that it possibly plays a role in the regulation of meiotic and post-meiotic factors. In this study, we reported an unprecedented way that the OdsH gene originated in the Drosophilinae ancestor. We also found that it has characteristics allowing us to propose its neofunctionalization in male sexual functions rapidly after its origin.
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Palavras-chave
Duplicação gênica, Homeodomínios, Neofuncionalização, Fator de transcrição, Drosophilidae, Gene duplication, Homeodomain, Neofunctionalization, Transcription factor