Receptores de cabo de guerra para sabor azedo em moscas da fruta lana§am luz sobre a biologia do sabor humano
Ao saborear um alimento a¡cido, o cérebro da mosca avalia a ativaa§a£o de ambas as populaa§aµes de neura´nios e decide se deve escolher ou rejeitar o alimento a¡cido , com base no tipo de neura´nio que vence.
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Neura´nios receptores gustativos de moscas (verdes) responsa¡veis ​​pela detecção de a¡cidos no ambiente alimentar. Crédito: Yali Zhang, Monell Chemical Senses Center
O sabor a¡cido não tem o apelo quase universal que o sabor doce tem. Alimentos ou bebidas ligeiramente azedos, como iogurte e suco de lima£o, são saborosos para muitos, mas alimentos altamente azedos, como leite estragado, são nojentos e atémesmo perigosos. Como os humanos, muitos outros animais, incluindo insetos, preferem alimentos ligeiramente a¡cidos a alimentos muito a¡cidos.
Os bia³logos evolucionistas supaµem que a necessidade de detecção de a¡cido para ser ajustada com precisão éuma moeda de dois lados: alimentos levemente a¡cidos podem melhorar a digestãoe estimular a produção de saliva; o sabor relativo entre o a¡cido e o doce pode sinalizar o amadurecimento ideal da fruta; e alimentos extremamente a¡cidos, como de sabor amargo , são um aviso para o que não ingerir. No entanto, apesar dessa utilidade, como os animais discernem diferentes concentrações de a¡cido para produzir comportamentos alimentares contrastantes usando o mesmo sistema de sabor azedo?
Um grupo de pesquisa liderado por Yali Zhang, Ph.D., Pesquisador Principal do Monell Chemical Senses Center, abordou recentemente esta questãode longa data. Seu trabalho foi publicado recentemente na Nature Communications .
Usando a mosca da fruta como modelo de pesquisa, Zhang e sua equipe se propuseram a elucidar como os animais distinguem entre baixas e altas concentrações de a¡cido. "Escolhemos as moscas porque elas não apenas nos ajudam a identificar os componentes genanãticos envolvidos na transdução do sabor, mas também exibem respostas de sabor pronunciadas e distintas a uma gama de concentrações de a¡cido em comparação com outros modelos animais", disse Zhang.
Sua equipe, incluindo os autores Tingwei Mi, John Mack e Christopher Lee do Monell Center e da Universidade da Pensilva¢nia, descobriram que as moscas usam dois tipos distintos de neura´nios receptores gustativos (GRNs), que são ana¡logos a s células receptoras gustativas em mamaferos , para discriminar ligeiramente os alimentos altamente a¡cidos. Um grupo de GRNs éativado ao ma¡ximo pela baixa acidez, enquanto o outro grupo apresentou suas melhores respostas a alta acidez. Ao saborear um alimento a¡cido, o cérebro da mosca avalia a ativação de ambas as populações de neura´nios e decide se deve escolher ou rejeitar o alimento a¡cido , com base no tipo de neura´nio que vence.
"Ficamos emocionados ao descobrir que o comportamento de gosto a¡cido de uma mosca éditado por um 'cabo de guerra' entre células receptoras de sabor com baixa e alta sensibilidade a a¡cidos", disse Zhang. Esse sistema bina¡rio de sabor azedo pode explicar por que muitos animais, incluindo humanos, são atraados por a¡cidos, mas repelidos por altas concentrações.
Além disso, o grupo de Zhang identificou uma proteana de mosca chamada Otopetrin-like (OtopLa), que tem uma contraparte ana¡loga em humanos, como um receptor de sabor azedo hámuito procurado. OtopLa forma um canal de aon seletivo para pra³tons que éespecificamente necessa¡rio para uma resposta atraente de sabor azedo. Notavelmente, as moscas mutantes sem OtopLa são avessas a baixas concentrações de a¡cido, bem como repelidas por concentrações mais altas.
"Atéonde sei, OtopLa éo primeiro receptor de sabor a ser identificado que éevolutivamente conservado entre insetos e mamaferos", disse Zhang. Este trabalho derruba a visão estabelecida de que insetos e mamaferos fazem uso de diferentes classes de receptores gustativos.
"Acredito que nossa pesquisa sobre a sensação de a¡cido em moscas pode avana§ar muito em nossa compreensão da codificação do sabor azedo em outros animais, incluindo humanos", disse Zhang.