Zebrafish sox9b is crucial for hepatopancreatic duct development and pancreatic endocrine cell regeneration

Unit of Molecular Biology and Genetic Engineering, Giga-Research, University of Liège, 1 avenue de l'Hôpital B34, B-4000 Sart-Tilman, Belgium.
Developmental Biology (Impact Factor: 3.55). 04/2012; 366(2):268-78. DOI: 10.1016/j.ydbio.2012.04.002
Source: PubMed


Recent zebrafish studies have shown that the late appearing pancreatic endocrine cells are derived from pancreatic ducts but the regulatory factors involved are still largely unknown. Here, we show that the zebrafish sox9b gene is expressed in pancreatic ducts where it labels the pancreatic Notch-responsive cells previously shown to be progenitors. Inactivation of sox9b disturbs duct formation and impairs regeneration of beta cells from these ducts in larvae. sox9b expression in the midtrunk endoderm appears at the junction of the hepatic and ventral pancreatic buds and, by the end of embryogenesis, labels the hepatopancreatic ductal system as well as the intrapancreatic and intrahepatic ducts. Ductal morphogenesis and differentiation are specifically disrupted in sox9b mutants, with the dysmorphic hepatopancreatic ducts containing misdifferentiated hepatocyte-like and pancreatic-like cells. We also show that maintenance of sox9b expression in the extrapancreatic and intrapancreatic ducts requires FGF and Notch activity, respectively, both pathways known to prevent excessive endocrine differentiation in these ducts. Furthermore, beta cell recovery after specific ablation is severely compromised in sox9b mutant larvae. Our data position sox9b as a key player in the generation of secondary endocrine cells deriving from pancreatic ducts in zebrafish.

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Available from: Bernard Peers, Oct 02, 2015
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    • "We then verified whether Notch signaling, reported to be upregulated during both chronic inflammation and early stages of tumorigenesis, could play a main role (Su et al., 2006). We observed a strong increase in Notch reporter activity in acinar cells of the exocrine pancreas from Tg(ptf1a:Gal4)/UAS:eGFP-KRAS G12D injected animals (Fig. 5C,D) compared with Tg(ptf1a:eGFP) controls in which the reporter expression was totally ductal (Manfroid et al., 2012). By quantitative analysis, we documented a significant increase in Notch reporter activity at 5 dpf, which consistently remained upregulated at 60 dpf (Fig. 5F). "
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    ABSTRACT: Pancreatic adenocarcinoma, one of the worst malignancies of exocrine pancreas, is a solid tumor with increasing incidence and mortality in industrialized countries. It is usually driven by oncogenic Kras point mutations and evolves into a highly aggressive metastatic carcinoma due to secondary gene mutations and specific signaling pathways unbalance. To examine in vivo the effects of Kras(G12D) during pancreatic cancer progression and time correlation with cancer signaling pathways activities, we have generated a zebrafish model of Pancreatic adenocarcinoma in which eGFP-Kras(G12D) expression was specifically driven to the pancreatic tissue by using the GAL4/UAS conditional expression system. Outcrossing the inducible oncogenic Kras(G12D) line with transgenic zebrafish reporters harboring specific signaling responsive elements of transcriptional effectors, we were able to follow TGFβ, Notch, Bmp and Shh activities during tumor development. Zebrafish transgenic lines expressing eGFP-Kras(G12D) showed normal exocrine pancreas development till 3 weeks post fertilization (wpf). From 4 to 24 wpf we observed several degree of acinar lesions, characterized by an increase of mesenchymal cells and mixed acinar/ductal features followed by progressive bowel and liver infiltrations finally bringing to highly aggressive carcinoma. Moreover, live imaging analysis of the exocrine pancreatic tissue revealed an increasing number of Kras positive cells and progressive activation of TGFβ; and Notch pathways. Increase of TGFβ, following Kras(G12D) activation, was confirmed in a concomitant model of medulloblastoma (MDB). Notch and Shh signaling activities during tumor onset were different between MDB and pancreatic adenocarcinoma indicating a tissue specific regulation of cell signaling pathways. Moreover, our results shows that a living model of pancreatic adenocarcinoma joined with cell signaling reporters is a suitable tool to describe in vivo the signaling cascades and molecular mechanisms involved in tumor development and a potential platform to screen for novel oncostatic drugs.
    Disease Models and Mechanisms 05/2014; 7(7). DOI:10.1242/dmm.014969 · 4.97 Impact Factor
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    • "This is in agreement with the absence of neurog3 expression in the intrapancreatic ducts of LY411575-treated embryos (data not shown). In contrast, we detected a strong expression of ascl1b in the intrapancreatic ducts of the LY411575-treated embryos (Figure 11C) as well as of neurod1 as previously described [48,49], suggesting that the couple Neurod1 and Ascl1b could also play an important role in the formation of second wave endocrine cells. The verification of this hypothesis will require the generation of ascl1b and neurod1 null mutant as the knock-down of Neurod1 is no longer fully efficient after 48 hpf. "
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    ABSTRACT: NEUROG3 is a key regulator of pancreatic endocrine cell differentiation in mouse, essential for the generation of all mature hormone producing cells. It is repressed by Notch signaling that prevents pancreatic cell differentiation by maintaining precursors in an undifferentiated state. We show herein that, in zebrafish, neurog3 is not expressed in the pancreas and null neurog3 mutant embryos do not display any apparent endocrine defects. The control of endocrine cell fate is instead fulfilled by a couple of bHLH factors, Ascl1b and Neurod1, that are both repressed by Notch signaling. ascl1b is transiently expressed in the mid-trunk endoderm just after gastrulation and is required for the generation of the first pancreatic endocrine precursor cells. Neurod1 is expressed afterwards in the pancreatic anlagen and pursues the endocrine cell differentiation program initiated by Ascl1b. Their complementary role in endocrine differentiation of the dorsal bud is demonstrated by the loss of all hormone-secreting cells following their simultaneous inactivation. This defect is due to a blockage of the initiation of endocrine cell differentiation. This study demonstrates that NEUROG3 is not the unique pancreatic endocrine cell fate determinant in vertebrates. A general survey of endocrine cell fate determinants in the whole digestive system among vertebrates indicates that they all belong to the ARP/ASCL family but not necessarily to the Neurog3 subfamily. The identity of the ARP/ASCL factor involved depends not only on the organ but also on the species. One could therefore consider differentiating stem cells into insulin-producing cells without the involvement of NEUROG3 but via another ARP/ASCL factor.
    BMC Biology 07/2013; 11(1):78. DOI:10.1186/1741-7007-11-78 · 7.98 Impact Factor
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    ABSTRACT: Tumors are largely classified by histologic appearance, yet morphologic features do not necessarily predict cellular origin. To determine the origin of pancreatic ductal adenocarcinoma (PDA), we labeled and traced pancreatic cell populations after induction of a PDA-initiating Kras mutation. Our studies reveal that ductal and stem-like centroacinar cells are surprisingly refractory to oncogenic transformation, whereas acinar cells readily form PDA precursor lesions with ductal features. We show that formation of acinar-derived premalignant lesions depends on ectopic induction of the ductal gene Sox9. Moreover, when concomitantly expressed with oncogenic Kras, Sox9 accelerates formation of premalignant lesions. These results provide insight into the cellular origin of PDA and suggest that its precursors arise via induction of a duct-like state in acinar cells.
    Cancer cell 11/2012; 22(6). DOI:10.1016/j.ccr.2012.10.025 · 23.52 Impact Factor
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