RESUMO
Genome-encoded microRNAs (miRNAs) provide a post-transcriptional regulatory layer that is important for pancreas development. However, how specific miRNAs are intertwined into the transcriptional network, which controls endocrine differentiation, is not well understood. Here, we show that microRNA-7 (miR-7) is specifically expressed in endocrine precursors and in mature endocrine cells. We further demonstrate that Pax6 is an important target of miR-7. miR-7 overexpression in developing pancreas explants or in transgenic mice led to Pax6 downregulation and inhibition of α- and ß-cell differentiation, resembling the molecular changes caused by haploinsufficient expression of Pax6. Accordingly, miR-7 knockdown resulted in Pax6 upregulation and promoted α- and ß-cell differentiation. Furthermore, Pax6 downregulation reversed the effect of miR-7 knockdown on insulin promoter activity. These data suggest a novel miR-7-based circuit that ensures precise control of endocrine cell differentiation.
Assuntos
Ilhotas Pancreáticas/embriologia , Ilhotas Pancreáticas/metabolismo , MicroRNAs/genética , MicroRNAs/metabolismo , Pâncreas/embriologia , Pâncreas/metabolismo , Animais , Sequência de Bases , Diferenciação Celular/genética , Diferenciação Celular/fisiologia , Proteínas do Olho/antagonistas & inibidores , Proteínas do Olho/genética , Proteínas do Olho/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Técnicas de Silenciamento de Genes , Haploinsuficiência , Proteínas de Homeodomínio/antagonistas & inibidores , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Insulina/genética , Ilhotas Pancreáticas/citologia , Camundongos , Camundongos Endogâmicos ICR , Camundongos Transgênicos , MicroRNAs/antagonistas & inibidores , Modelos Biológicos , Técnicas de Cultura de Órgãos , Fator de Transcrição PAX6 , Fatores de Transcrição Box Pareados/antagonistas & inibidores , Fatores de Transcrição Box Pareados/genética , Fatores de Transcrição Box Pareados/metabolismo , Pâncreas/citologia , Regiões Promotoras Genéticas , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Repressoras/antagonistas & inibidores , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Regulação para CimaRESUMO
Genome-encoded microRNAs (miRNAs) provide a posttranscriptional regulatory layer, which is important for pancreas development. Differentiation of endocrine cells is controlled by a network of pancreatic transcription factors including Ngn3 and NeuroD/Beta2. However, how specific miRNAs are intertwined into this transcriptional network is not well understood. Here, we characterize the regulation of microRNA-7 (miR-7) by endocrine-specific transcription factors. Our data reveal that three independent miR-7 genes are coexpressed in the pancreas. We have identified conserved blocks upstream of pre-miR-7a-2 and pre-miR-7b and demonstrated by functional assays that they possess promoter activity, which is increased by the expression of NeuroD/Beta2. These data suggest that the endocrine specificity of miR-7 expression is governed by transcriptional mechanisms and involves members of the pancreatic endocrine network of transcription factors.