ABSTRACT
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.
Subject(s)
Islets of Langerhans/embryology , Islets of Langerhans/metabolism , MicroRNAs/genetics , MicroRNAs/metabolism , Pancreas/embryology , Pancreas/metabolism , Animals , Base Sequence , Cell Differentiation/genetics , Cell Differentiation/physiology , Eye Proteins/antagonists & inhibitors , Eye Proteins/genetics , Eye Proteins/metabolism , Gene Expression Regulation, Developmental , Gene Knockdown Techniques , Haploinsufficiency , Homeodomain Proteins/antagonists & inhibitors , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Insulin/genetics , Islets of Langerhans/cytology , Mice , Mice, Inbred ICR , Mice, Transgenic , MicroRNAs/antagonists & inhibitors , Models, Biological , Organ Culture Techniques , PAX6 Transcription Factor , Paired Box Transcription Factors/antagonists & inhibitors , Paired Box Transcription Factors/genetics , Paired Box Transcription Factors/metabolism , Pancreas/cytology , Promoter Regions, Genetic , RNA, Messenger/genetics , RNA, Messenger/metabolism , Repressor Proteins/antagonists & inhibitors , Repressor Proteins/genetics , Repressor Proteins/metabolism , Up-RegulationABSTRACT
The specific program that enables the stereotypic differentiation of specialized cartilages, including the trachea, is intrinsically distinct from the program that gives rise to growth plate hypertrophic chondrocytes. For example, Snail1 is an effector of FGF signaling in growth plate pre-hypertrophic chondrocytes, but it derails the normal program of permanent chondrocytes, repressing the transcription of Aggrecan and Collagen type 2a1 (Col2a1). Here we show that miRNA activity is essential for normal trachea development and that miR-125b and miR-30a/c keep Snail1 at low levels, thus enabling full functional differentiation of Col2a1 tracheal chondrocytes. Specific inhibition of miR-125b and miR-30a/c in chondrocytes or Dicer1 knockout in the trachea, de-repress Snail1. As a consequence, the transcription of Aggrecan and Col2a1 is hampered and extracellular matrix deposition is decreased. Our data reveals a new miRNA pathway that is safekeeping the specific genetic program of differentiated and matrix-producing tracheal chondrocytes from acquisition of unwanted signals. This pathway may improve understanding of human primary tracheomalacia and improve protocols for cartilage tissue engineering.
