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Imunidade e especiação: o papel do gene TEP1 na divergência entre formas moleculares do vector de malária Anopheles gambiae (Diptera: Culicidae).
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Resumo(s)
Anopheles gambiae s.s., principal vector de malária em África, atravessa um
processo de especiação incipiente representado por duas formas moleculares,
designadas por M e S. Os mecanismos que conduziram a este processo continuam por
esclarecer, mas verificou-se que a forma M está associada a biótopos larvares
permanentes, com maior pressão de predadores e agentes patogénicos, e a forma S a
criadouros temporários, onde essa pressão é menor. Recentemente, foi sugerida a
importância do gene TEP1, envolvido na resposta imunitária do mosquito a agentes
patogénicos, neste processo de especiação. Em locais onde M e S ocorrem em
simpatria, observaram-se elevadas frequências de um alelo associado à resistência à
infecção por Plasmodium sp na forma M e a sua ausência na forma S. Para testar a
possibilidade da frequência elevada deste alelo na forma M ser uma consequência de
pressão selectiva na fase larvar, foram analisados os padrões de variação do gene TEP1
entre formas moleculares em diferentes criadouros larvares.
Em 2010, foram feitas colheitas entomológicas de larvas em criadouros
permanentes e temporários e de adultos em Antula, Guiné-Bissau, um dos raros locais
onde se observaram elevadas frequências de hibridização entre M e S. Foi feita a
identificação molecular das espécies e formas moleculares do complexo An. gambiae
através dos marcadores IGS e SINE200X1.6. O gene TEP1 foi genotipado por PCRRFLP
e um fragmento de 450pb do domínio TED deste gene foi sequenciado.
Surpreendentemente, a espécie Anopheles arabiensis foi identificada pela
primeira vez na região de Antula. Este achado pode ser resultado de uma introdução
recente deste vector nesta região.
Problemas técnicos na identificação molecular das larvas do criadouro
permanente impediram a análise dos padrões de variação do gene TEP1 entre diferentes
tipos de criadouros larvares. Observou-se uma elevada frequência do alelo susceptível
S1 do gene TEP1 e baixas frequências dos alelos resistentes R1 e R2. Apesar da elevada
taxa de hibridação entre formas, o alelo R1 ocorreu associado exclusivamente à forma
M que, consequentemente, apresentou uma maior diversidade genética, possivelmente
devido a um processo de selecção balanceada. A forma S apresentou uma diversidade
genética inferior, possivelmente como consequência de um processo de selecção
positiva.
The main malaria vector in Africa, Anopheles gambiae s.s., is undergoing a process of incipient speciation, represented by two molecular forms denoted M and S. The mechanisms that lead to this process are not entirely understood, but it was shown that M form is associated with permanent breeding sites, with higher levels of predation and/or pathogen pressure, whereas S form is associated with temporary breeding sites, where this pressure is lower. Recently, it was suggested that the TEP1 gene, a gene involved in the mosquito immune response, may have a role in this speciation process. In areas where M and S occur in sympatry, high frequencies of an allele associated with Plasmodium sp infection resistance where reported in the M form, while this allele was absent in the S form. To test the possibility that this high frequency in the M form is a consequence of selection acting on larval stages, genetic variation patterns at the TEP1 gene between molecular forms and different breeding sites was analyzed. In 2010, larval sampling at temporary and permanent breeding sites and adult sampling was performed in Antula, Guinea Bissau, one of the rare places where high levels of hybridization between M and S forms were found. Molecular identification of species and molecular forms within the An. gambiae complex were performed using IGS and SINE200X1.6 markers. The TEP1 gene was genotyped and a 450bp fragment from the TED domain of this gene was sequenced. Surprisingly, An. arabiensis was identified for the very first time in Antula region. This finding may correspond to a recent introduction of this vector species in this region. It was impossible to analyze the variation patterns of TEP1 gene between different breeding sites due to technical problems in the identification of larvae from permanent breeding sites. High frequency of TEP1*S1 allele was observed in this region, while low frequencies of R1 and R2 alleles were observed. In spite of the high hybridization levels, the R1 allele was exclusively associated with M form, which presented a higher genetic diversity, probably as consequence of a process of balancing selection. The S form presented a lower genetic diversity, probably as consequence of a process of positive selection.
The main malaria vector in Africa, Anopheles gambiae s.s., is undergoing a process of incipient speciation, represented by two molecular forms denoted M and S. The mechanisms that lead to this process are not entirely understood, but it was shown that M form is associated with permanent breeding sites, with higher levels of predation and/or pathogen pressure, whereas S form is associated with temporary breeding sites, where this pressure is lower. Recently, it was suggested that the TEP1 gene, a gene involved in the mosquito immune response, may have a role in this speciation process. In areas where M and S occur in sympatry, high frequencies of an allele associated with Plasmodium sp infection resistance where reported in the M form, while this allele was absent in the S form. To test the possibility that this high frequency in the M form is a consequence of selection acting on larval stages, genetic variation patterns at the TEP1 gene between molecular forms and different breeding sites was analyzed. In 2010, larval sampling at temporary and permanent breeding sites and adult sampling was performed in Antula, Guinea Bissau, one of the rare places where high levels of hybridization between M and S forms were found. Molecular identification of species and molecular forms within the An. gambiae complex were performed using IGS and SINE200X1.6 markers. The TEP1 gene was genotyped and a 450bp fragment from the TED domain of this gene was sequenced. Surprisingly, An. arabiensis was identified for the very first time in Antula region. This finding may correspond to a recent introduction of this vector species in this region. It was impossible to analyze the variation patterns of TEP1 gene between different breeding sites due to technical problems in the identification of larvae from permanent breeding sites. High frequency of TEP1*S1 allele was observed in this region, while low frequencies of R1 and R2 alleles were observed. In spite of the high hybridization levels, the R1 allele was exclusively associated with M form, which presented a higher genetic diversity, probably as consequence of a process of balancing selection. The S form presented a lower genetic diversity, probably as consequence of a process of positive selection.
Descrição
Palavras-chave
Parasitologia médica Anopheles gambiae Formas moleculares Criadouros larvares Especiação incipiente Gene TEP1
Contexto Educativo
Citação
Editora
Instituto de Higiene e Medicina Tropical