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ABSTRACT: OBJECTIVES: Emerging evidence from mouse models suggests that mutant Kras can drive the development of pancreatic ductal adenocarcinoma (PDA) precursors from acinar cells by enforcing ductal de-differentiation at the expense of acinar identity. Recently, human genome-wide association studies have identified NR5A2, a key regulator of acinar function, as a susceptibility locus for human PDA. We investigated the role of Nr5a2 in exocrine maintenance, regeneration and Kras driven neoplasia. DESIGN: To investigate the function of Nr5a2 in the pancreas, we generated mice with conditional pancreatic Nr5a2 deletion (PdxCre(late); Nr5a2(c/c)). Using this model, we evaluated acinar differentiation, regeneration after caerulein pancreatitis and Kras driven pancreatic neoplasia in the setting of Nr5a2 deletion. RESULTS: We show that Nr5a2 is not required for the development of the pancreatic acinar lineage but is important for maintenance of acinar identity. Nr5a2 deletion leads to destabilisation of the mature acinar differentiation state, acinar to ductal metaplasia and loss of regenerative capacity following acute caerulein pancreatitis. Loss of Nr5a2 also dramatically accelerates the development of oncogenic Kras driven acinar to ductal metaplasia and PDA precursor lesions. CONCLUSIONS: Nr5a2 is a key regulator of acinar plasticity. It is required for maintenance of acinar identity and re-establishing acinar fate during regeneration. Nr5a2 also constrains pancreatic neoplasia driven by oncogenic Kras, providing functional evidence supporting a potential role as a susceptibility gene for human PDA.
Gut 05/2013; · 10.11 Impact Factor
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ABSTRACT: Pancreatic multipotent progenitor cells (MPCs) produce acinar, endocrine and duct cells during organogenesis, but their existence and location in the mature organ remain contentious. We used inducible lineage-tracing from the MPC-instructive gene Ptf1a to define systematically in mice the switch of Ptf1a(+) MPCs to unipotent proacinar competence during the secondary transition, their rapid decline during organogenesis, and absence from the mature organ. Between E11.5 and E15.5, we describe tip epithelium heterogeneity, suggesting that putative Ptf1a(+)Sox9(+)Hnf1β(+) MPCs are intermingled with Ptf1a(HI)Sox9(LO) proacinar progenitors. In the adult, pancreatic duct ligation (PDL) caused facultative reactivation of multipotency factors (Sox9 and Hnf1β) in Ptf1a(+) acini, which undergo rapid reprogramming to duct cells and longer-term reprogramming to endocrine cells, including insulin(+) β-cells that are mature by the criteria of producing Pdx1(HI), Nkx6.1(+) and MafA(+). These Ptf1a lineage-derived endocrine/β-cells are likely formed via Ck19(+)/Hnf1β(+)/Sox9(+) ductal and Ngn3(+) endocrine progenitor intermediates. Acinar to endocrine/β-cell transdifferentiation was enhanced by combining PDL with pharmacological elimination of pre-existing β-cells. Thus, we show that acinar cells, without exogenously introduced factors, can regain aspects of embryonic multipotentiality under injury, and convert into mature β-cells.
Development 01/2013; · 6.60 Impact Factor
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Janel L Kopp,
Guido von Figura,
Erin Mayes,
Fen-Fen Liu,
Claire L Dubois,
John P Morris,
Fong Cheng Pan,
Haruhiko Akiyama, Christopher V E Wright,
Kristin Jensen,
Matthias Hebrok,
Maike Sander
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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; · 25.29 Impact Factor
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ABSTRACT: The Notch signaling pathway regulates embryonic development of the pancreas, inhibiting progenitor differentiation into exocrine acinar and endocrine islet cells. The adult pancreas appears to lack progenitor cells, and its mature cell types are maintained by the proliferation of pre-existing differentiated cells. Nonetheless, Notch remains active in adult duct and terminal duct/centroacinar cells (CACs), in which its function is unknown. We previously developed mice in which cells expressing the Notch target gene Hes1 can be labeled and manipulated, by expression of Cre recombinase, and demonstrated that Hes1(+) CACs do not behave as acinar or islet progenitors in the uninjured pancreas, or as islet progenitors after pancreatic duct ligation. In the current study, we assessed the function of Notch signaling in the adult pancreas by deleting the transcription factor partner of Notch, Rbpj, specifically in Hes1(+) cells. We find that loss of Rbpj depletes the pancreas of Hes1-expressing CACs, abrogating their ongoing contribution to growth and homeostasis of more proximal duct structures. Upon Rbpj deletion, CACs undergo a rapid transformation into acinar cells, suggesting that constitutive Notch activity suppresses the acinar differentiation potential of CACs. Together, our data provide direct evidence of an endogenous genetic program to control interconversion of cell fates in the adult pancreas.
Developmental Biology 11/2011; 362(1):57-64. · 4.07 Impact Factor
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Hideaki Ijichi,
Anna Chytil,
Agnieszka E Gorska,
Mary E Aakre,
Brian Bierie,
Motohisa Tada,
Dai Mohri,
Koji Miyabayashi,
Yoshinari Asaoka,
Shin Maeda,
Tsuneo Ikenoue,
Keisuke Tateishi, Christopher V E Wright,
Kazuhiko Koike,
Masao Omata,
Harold L Moses
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ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC), one of the most lethal neoplasms, is characterized by an expanded stroma with marked fibrosis (desmoplasia). We previously generated pancreas epithelium-specific TGF-β receptor type II (Tgfbr2) knockout mice in the context of Kras activation (mice referred to herein as Kras+Tgfbr2KO mice) and found that they developed aggressive PDAC that recapitulated the histological manifestations of the human disease. The mouse PDAC tissue showed strong expression of connective tissue growth factor (Ctgf), a profibrotic and tumor-promoting factor, especially in the tumor-stromal border area, suggesting an active tumor-stromal interaction. Here we show that the PDAC cells in Kras+Tgfbr2KO mice secreted much higher levels of several Cxc chemokines compared with mouse pancreatic intraepithelial neoplasia cells, which are preinvasive. The Cxc chemokines induced Ctgf expression in the pancreatic stromal fibroblasts, not in the PDAC cells themselves. Subcutaneous grafting studies revealed that the fibroblasts enhanced growth of PDAC cell allografts, which was attenuated by Cxcr2 inhibition. Moreover, treating the Kras+Tgfbr2KO mice with the CXCR2 inhibitor reduced tumor progression. The decreased tumor progression correlated with reduced Ctgf expression and angiogenesis and increased overall survival. Taken together, our data indicate that tumor-stromal interactions via a Cxcr2-dependent chemokine and Ctgf axis can regulate PDAC progression. Further, our results suggest that inhibiting tumor-stromal interactions might be a promising therapeutic strategy for PDAC.
The Journal of clinical investigation 09/2011; 121(10):4106-17. · 15.39 Impact Factor
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ABSTRACT: Fluorescent protein (FP) reporter alleles are useful both for identifying and purifying specific cell populations in the mouse. Here, we report the generation of mouse embryonic stem cells that contain a pancreatic and duodenal homeobox 1 (Pdx1) loxed cassette acceptor (Pdx1(LCA)) allele and the use of recombinase-mediated cassette exchange to derive mice that contain a Pdx1(CFP) (Cerulean) reporter allele. Mice with this allele exhibited cyan fluorescence within the previously well-characterized Pdx1 expression domain in posterior foregut endoderm. Immunolabeling showed that endogenous Pdx1 was coexpressed with CFP at all time points examined. Furthermore, fluorescence-activated cell sorting was used to isolate CFP-positive cells from E11.5 and E18.5 embryonic tissues using both 405 and 445 nm lasers, although the latter resulted in a nearly 50-fold increase in emission intensity. The Pdx1(CFP) allele will enable the isolation of specific foregut endoderm and pancreatic cell populations, both alone and in combination with other FP reporter alleles.
genesis 09/2011; 50(4):384-92. · 2.53 Impact Factor
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ABSTRACT: Using single transcription factors to reprogram cells could produce important insights into the epigenetic mechanisms that direct normal differentiation, or counter inappropriate plasticity, or even provide new ways of manipulating normal ontogeny in vitro to control lineage diversification and differentiation. We enforced Pdx1 expression from the Neurogenin-3-expressing endocrine commitment point onward and found during the embryonic period a minor increased β-cell allocation with accompanying reduced α-cell numbers. More surprisingly, almost all remaining Pdx1-containing glucagon/Arx-producing cells underwent a fairly rapid conversion at postnatal stages, through glucagon-insulin double positivity, to a state indistinguishable from normal β cells, resulting in complete α-cell absence. This α-to-β conversion was not caused by activating Pdx1 in the later glucagon-expressing state. Our findings reveal that Pdx1 can work single-handedly as a potent context-dependent autonomous reprogramming agent, and suggest a postnatal differentiation evaluation stage involved in normal endocrine maturation.
Genes & development 08/2011; 25(16):1680-5. · 12.08 Impact Factor
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ABSTRACT: The basic helix-loop-helix transcription factor Neurog3 (Neurogenin3 or Ngn3) actively drives endodermal progenitor cells towards endocrine islet cell differentiation during embryogenesis. Here, we manipulate Neurog3 expression levels in endocrine progenitor cells without altering its expression pattern using heterozygosity and a hypomorph. Lowered Neurog3 gene dosage in the developing pancreatic epithelium reduces the overall production of endocrine islet cells without significantly affecting the proportions of various islet cell types that do form. A reduced Neurog3 production level in the endocrine-directed pancreatic progenitor population activates the expression of Neurog3 in an increased number of epithelial progenitors. Yet a significant number of these Neurog3+ cells detected in heterozygous and hypomorphic pancreata, possibly those that express low levels of Neurog3, move on to adopt pancreatic ductal or acinar fates. These data directly demonstrate that achieving high levels of Neurog3 expression is a critical step for endocrine commitment from multipotent pancreatic progenitors. These findings also suggest that a high level of Neurog3 expression could mediate lateral inhibition or other unknown feedback mechanisms to regulate the number of cells that initiate Neurog3 transcription and protein production. The control of Neurog3+ cell number and the Neurog3 threshold-dependent endocrine differentiation mechanism combine to select a specific proportion of pancreatic progenitor cells to adopt the islet cell fate.
Developmental Biology 12/2009; 339(1):26-37. · 4.07 Impact Factor
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ABSTRACT: GABAergic interneurons are key elements in neural coding, but the mechanisms that assemble inhibitory circuits remain unclear. In the spinal cord, the transfer of sensory signals to motor neurons is filtered by GABAergic interneurons that act presynaptically to inhibit sensory transmitter release and postsynaptically to inhibit motor neuron excitability. We show here that the connectivity and synaptic differentiation of GABAergic interneurons that mediate presynaptic inhibition is directed by their sensory targets. In the absence of sensory terminals these GABAergic neurons shun other available targets, fail to undergo presynaptic differentiation, and withdraw axons from the ventral spinal cord. A sensory-specific source of brain derived neurotrophic factor induces synaptic expression of the GABA synthetic enzyme GAD65--a defining biochemical feature of this set of interneurons. The organization of a GABAergic circuit that mediates presynaptic inhibition in the mammalian CNS is therefore controlled by a stringent program of sensory recognition and signaling.
Cell 10/2009; 139(1):161-74. · 32.40 Impact Factor
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Akihisa Fukuda,
Yoshiya Kawaguchi,
Kenichiro Furuyama,
Sota Kodama,
Masashi Horiguchi,
Takeshi Kuhara,
Michiya Kawaguchi,
Mami Terao,
Ryuichiro Doi, Christopher V E Wright,
Mikio Hoshino,
Tsutomu Chiba,
Shinji Uemoto
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ABSTRACT: Most pancreatic endocrine cells derive from Ptf1a-expressing progenitor cells. In humans, nonsense mutations in Ptf1a have recently been identified as a cause of permanent neonatal diabetes associated with pancreatic agenesis. The death of Ptf1a-null mice soon after birth has not allowed further insight into the pathogenesis of the disease; it is therefore unclear how much pancreatic endocrine function is dependent on Ptf1a in mammals. This study aims to investigate gene-dosage effects of Ptf1a on pancreas development and function in mice.
Combining hypomorphic and null alleles of Ptf1a and Cre-mediated lineage tracing, we followed the cell fate of reduced Ptf1a-expressing progenitors and analyzed pancreas development and function in mice.
Reduced Ptf1a dosage resulted in pancreatic hypoplasia and glucose intolerance with insufficient insulin secretion in a dosage-dependent manner. In hypomorphic mutant mice, pancreatic bud size was small and substantial proportions of pancreatic progenitors were misspecified to the common bile duct and duodenal cells. Growth with branching morphogenesis and subsequent exocrine cytodifferentiation was reduced and delayed. Total beta-cell number was decreased, proportion of non-beta islet cells was increased, and alpha-cells were abnormally intermingled with beta-cells. Interestingly, Pdx1 expression was decreased in early pancreatic progenitors but elevated to normal level at the mid-to-late stages of pancreatogenesis. CONCLUSIONS-The dosage of Ptf1a is crucial for pancreas specification, growth, total beta-cell number, islet morphogenesis, and endocrine function. Some neonatal diabetes may be caused by mutation or single nucleotide polymorphisms in the Ptf1a gene that reduce gene expression levels.
Diabetes 07/2008; 57(9):2421-31. · 8.29 Impact Factor
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ABSTRACT: The pancreas is derived from a pool of multipotent progenitor cells (MPCs) that co-express Pdx-1 and Ptf1a. To more precisely define how the individual and combined loss of Pdx-1 and Ptf1a affects pancreatic MPC specification and differentiation we derived and studied mice bearing a novel Ptf1a(YFP) allele. While the expression of Pdx-1 and Ptf1a in pancreatic MPCs coincides between E9.5 and 12.5 the developmental phenotypes of Pdx-1 null and Pdx-1; Ptf1a double null mice are indistinguishable, and an early pancreatic bud is formed in both cases. This finding indicates that Pdx-1 is required in the foregut endoderm prior to Ptf1a for pancreatic MPC specification. We also found that Ptf1a is neither required for specification of Ngn3-positive endocrine progenitors nor differentiation of mature beta-cells. In the absence of Pdx-1 Ngn3-positive cells were not observed after E9.5. Thus, in contrast to the deletion of Ptf1a, the loss of Pdx-1 precludes the sustained Ngn3-based derivation of endocrine progenitors from pancreatic MPCs. Taken together, these studies indicate that Pdx-1 and Ptf1a have distinct but interdependent functions during pancreatic MPC specification.
Developmental Biology 05/2008; 316(1):74-86. · 4.07 Impact Factor
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ABSTRACT: The pdx1 gene is essential for pancreatic organogenesis in humans and mice; pdx1 mutations have been identified in human diabetic patients. Specific inactivation of pdx1 in adult beta cells revealed that this gene is required for maintenance of mature beta cell function. In the following study, a Cre-lox strategy was used to remove pdx1 function specifically from embryonic beta cells beginning at late-gestation, prior to islet formation. Animals in which pdx1 is lost in insulin-producing cells during embryogenesis had elevated blood glucose levels at birth and were overtly diabetic by weaning. Neonatal and adult mutant islets showed a dramatic reduction in the number of insulin(+) cells and an increase in both glucagon(+) and somatostatin(+) cells. Lineage tracing revealed that excess glucagon(+) and somatostatin(+) cells did not arise by interconversion of endocrine cell types. Examination of mutant islets revealed a decrease in proliferation of insulin-producing cells just before birth and a concomitant increase in proliferation of glucagon-producing cells. We propose that pdx1 is required for proliferation and function of the beta cells generated at late gestation, and that one function of normal beta cells is to inhibit the proliferation of other islet cell types, resulting in the appropriate numbers of the different endocrine cell types.
Developmental Biology 03/2008; 314(2):406-17. · 4.07 Impact Factor
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ABSTRACT: The Nodal and Nodal-related morphogens are utilized for the specification of distinct cellular identity throughout development by activating discrete target genes in a concentration-dependant manner. Lefty is a principal extracellular antagonist involved in the spatiotemporal regulation of the Nodal morphogen gradient during mesendoderm induction. The Xenopus Lefty proprotein contains a single N-linked glycosylation motif in the mature domain and two potential cleavage sites that would be expected to produce long (Xlefty(L)) and short (Xlefty(S)) isoforms. Here we demonstrate that both isoforms were secreted from Xenopus oocytes, but that Xlefty(L) is the only isoform detected when embryonic tissue was analyzed. In mesoderm induction assays, Xlefty(L) is the functional blocker of Xnr signaling. When secreted from oocytes, vertebrate Lefty molecules were N-linked glycosylated. However, glycan addition was not required to inhibit Xnr signaling and did not influence its movement through the extracellular space. These findings demonstrate that Lefty molecules undergo post-translational modifications and that some of these modifications are required for the Nodal inhibitory function.
Developmental Dynamics 09/2007; 236(8):2050-61. · 2.54 Impact Factor
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ABSTRACT: The critical pancreatic transcription factor Pdx1 is expressed throughout the pancreas early but enriched in insulin-producing beta cells postnatally. Previous studies showed that the 5' conserved promoter regions areas I and II (Pdx1(PB)) direct endocrine cell expression, while an adjacent region (Pdx1(XB)) containing conserved area III directs transient beta-cell expression. In this study, we used Cre-mediated lineage tracing to track cells that activated these regions. Pdx1(PB)Cre mediated only endocrine cell recombination, while Pdx1(XB)Cre directed broad and early recombination in the developing pancreas. Also, a reporter transgene containing areas I, II, and III was expressed throughout the embryonic day 10.5 (E10.5) pancreas and gradually became beta cell enriched, similar to endogenous Pdx1. These data suggested that sequences within area III mediate early pancreas-wide Pdx1 expression. Area III contains a binding site for PTF1, a transcription factor complex essential for pancreas development. This site contributed to area III-dependent reporter gene expression in the acinar AR42J cell line, while PTF1 specifically trans-activated area III-containing reporter expression in a nonpancreatic cell line. Importantly, Ptf1a occupied sequences spanning the endogenous PTF1 site in area III of E11.5 pancreatic buds. These data strongly suggest that PTF1 is an important early activator of Pdx1 in acinar and endocrine progenitor cells during pancreas development.
Molecular and Cellular Biology 06/2007; 27(11):4093-104. · 5.53 Impact Factor
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ABSTRACT: Activation of sonic hedgehog (Shh) signaling occurs in the majority of pancreatic ductal adenocarcinomas. Here we investigate the mechanisms by which Shh contributes to pancreatic tumorigenesis. We find that Shh expression enhances proliferation of pancreatic duct epithelial cells, potentially through the transcriptional regulation of the cell cycle regulators cyclin D1 and p21. We further show that Shh protects pancreatic duct epithelial cells from apoptosis through the activation of phosphatidylinositol 3-kinase signaling and the stabilization of Bcl-2 and Bcl-X(L). Significantly, Shh also cooperates with activated K-Ras to promote pancreatic tumor development. Finally, Shh signaling enhances K-Ras-induced pancreatic tumorigenesis by reducing the dependence of tumor cells on the sustained activation of the MAPK and phosphatidylinositol 3-kinase/Akt/mTOR signaling pathways. Thus, our data suggest that Shh signaling contributes to tumor initiation in the pancreas through at least two mechanisms and additionally enhances tumor cell resistance to therapeutic intervention. Collectively, our findings demonstrate crucial roles for Shh signaling in multiple stages of pancreatic carcinogenesis.
Proceedings of the National Academy of Sciences 04/2007; 104(12):5103-8. · 9.68 Impact Factor
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ABSTRACT: Transient asymmetric Nodal signaling in the left lateral plate mesoderm (L LPM) during tailbud/early somitogenesis stages is associated in all vertebrates examined with the development of stereotypical left-right (L-R) organ asymmetry. In Xenopus, asymmetric expression of Nodal-related 1 (Xnr1) begins in the posterior L LPM shortly after the initiation of bilateral perinotochordal expression in the posterior tailbud. The L LPM expression domain rapidly shifts forward to cover much of the flank of the embryo before being progressively downregulated, also in a posterior-to-anterior direction. The mechanisms underlying the initiation and propagation of Nodal/Xnr1 expression in the L LPM, and its transient nature, are not well understood. Removing the posterior tailbud domain prevents Xnr1 expression in the L LPM, consistent with the idea that normal embryos respond to a posteriorly derived asymmetrically acting positive inductive signal. The forward propagation of asymmetric Xnr1 expression occurs LPM-autonomously via planar tissue communication. The shifting is prevented by Nodal signaling inhibitors, implicating an underlying requirement for Xnr1-to-Xnr1 induction. It is also unclear how asymmetric Nodal signals are modulated during L-R patterning. Small LPM grafts overexpressing Xnr1 placed into the R LPM of tailbud embryos induced the expression of the normally L-sided genes Xnr1, Xlefty, and XPitx2, and inverted body situs, demonstrating the late-stage plasticity of the LPM. Orthogonal Xnr1 signaling from the LPM strongly induced Xlefty expression in the midline, consistent with recent findings in the mouse and demonstrating for the first time in another species conservation in the mechanism that induces and maintains the midline barrier. Our findings suggest that there is long-range contralateral communication between L and R LPM, involving Xlefty in the midline, over a substantial period of tailbud embryogenesis, and therefore lend further insight into how, and for how long, the midline maintains a L versus R status in the LPM.
Developmental Biology 02/2007; 301(2):447-63. · 4.07 Impact Factor
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Yoshio Fujitani,
Shuko Fujitani,
Huijun Luo,
Feng Qiu,
Jared Burlison,
Qiaoming Long,
Yoshiya Kawaguchi,
Helena Edlund,
Raymond J MacDonald,
Takahisa Furukawa,
Takashi Fujikado,
Mark A Magnuson,
Mengqing Xiang, Christopher V E Wright
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ABSTRACT: The vertebrate neural retina comprises six classes of neurons and one class of glial cells, all derived from a population of multipotent progenitors. There is little information on the molecular mechanisms governing the specification of cell type identity from multipotent progenitors in the developing retina. We report that Ptf1a, a basic-helix-loop-helix (bHLH) transcription factor, is transiently expressed by post-mitotic precursors in the developing mouse retina. Recombination-based lineage tracing analysis in vivo revealed that Ptf1a expression marks retinal precursors with competence to exclusively produce horizontal and amacrine neurons. Inactivation of Ptf1a leads to a fate-switch in these precursors that causes them to adopt a ganglion cell fate. This mis-specification of neurons results in a complete loss of horizontal cells, a profound decrease of amacrine cells and an increase in ganglion cells. Furthermore, we identify Ptf1a as a primary downstream target for Foxn4, a forkhead transcription factor involved in the genesis of horizontal and amacrine neurons. These data, together with the previous findings on Foxn4, provide a model in which the Foxn4-Ptf1a pathway plays a central role in directing the differentiation of retinal progenitors towards horizontal and amacrine cell fates.
Development 12/2006; 133(22):4439-50. · 6.60 Impact Factor
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ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC) is an almost uniformly lethal disease in humans. Transforming growth factor-beta (TGF-beta) signaling plays an important role in PDAC progression, as indicated by the fact that Smad4, which encodes a central signal mediator downstream from TGF-beta, is deleted or mutated in 55% and the type II TGF-beta receptor (Tgfbr2) gene is altered in a smaller subset of human PDAC. Pancreas-specific Tgfbr2 knockout mice have been generated, alone or in the context of active Kras (Kras(G12D)) expression, using the Cre-loxP system driven by the endogenous Ptf1a (pancreatic transcription factor-1a) locus. Pancreas-selective Tgfbr2 knockout alone gave no discernable phenotype in 1.5 yr. Pancreas-specific Kras(G12D) activation alone essentially generated only intraepithelial neoplasia within 1 yr. In contrast, the Tgfbr2 knockout combined with Kras(G12D) expression developed well-differentiated PDAC with 100% penetrance and a median survival of 59 d. Heterozygous deletion of Tgfbr2 with Kras(G12D) expression also developed PDAC, which indicated a haploinsufficiency of TGF-beta signaling in this genetic context. The clinical and histopathological manifestations of the combined Kras(G12D) expression and Tgfbr2 knockout mice recapitulated human PDAC. The data show that blockade of TGF-beta signaling and activated Ras signaling cooperate to promote PDAC progression.
Genes & Development 12/2006; 20(22):3147-60. · 11.66 Impact Factor
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ABSTRACT: The unique, well-demarcated expression domain of Pdx1 within the posterior foregut suggests that investigating its transcriptional regulation will provide insight into mechanisms that regionally pattern the endoderm. Previous phylogenetic comparison identified conserved noncoding regions that stimulate transcriptional activity selectively in cultured pancreatic beta cells. Characterization of these regulatory elements is helping to dissect the transcription factor networks that operate within beta cells, which is important for understanding the etiology of beta cell dysfunction and diabetes, as well as for developing methods to produce beta cells in vitro for cell-based therapies. We recently reported that deletion of three proximally located conserved areas (Area I-II-III) from the endogenous Pdx1 locus resulted in severely reduced expression of Pdx1 in the pancreas, and a milder decrease in other foregut tissues. Here, we report transgene-based complementation experiments on Pdx1 null mice, which reveal that the proximal promoter/enhancer region, including Area I-II-III, rescues the pancreatic defects caused by Pdx1 deficiency, but only weakly promotes expression of Pdx1 in the postnatal stomach and duodenum. These results reveal a role for distal cis-regulatory elements in achieving the correct level of extra-pancreatic Pdx1 expression, which is necessary for the production of duodenal GIP cells and stomach gastrin cells.
Developmental Biology 11/2006; 298(2):616-31. · 4.07 Impact Factor
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ABSTRACT: In Xenopus, six nodal-related genes (Xnrs) have been identified to date. We found numerous tandem duplications of Xnr5 in the Xenopus laevis and Xenopus tropicalis genomes that involve highly conserved copies of coding and regulatory regions. The duplicated versions of Xnr5 were expressed in both the superficial and deep layer of dorsal endoderm and in the deep layer of ventral endoderm, where the initial inducers of mesendoderm formation would be expected to be localized. Overexpression of secreted inhibitors of Xnrs led to a substantially enhanced transcription of the duplicated Xnr5 genes and Xnr6 in embryos. Therefore, Xnr5 and Xnr6 have a novel feedback loop to inhibit transcription of Xnr5 and Xnr6. These results suggest that the initialization of a strong Xnr5 and Xnr6 signal is enabled by the rapid transcription from multiple genes. The novel feedback loop may negatively regulate transcription of Xnr5s and Xnr6 to limit overproduction of these potent inducers, with the Xnr5/Xnr6 signal then activating positive (Xnrs) and negative (Xlefty) loops, which regulate the range of mesodermal tissues produced.
genesis 08/2006; 44(7):309-21. · 2.53 Impact Factor
