| 1. |
- Greiner, Thomas U., 1977, et al.
(author)
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Rac1 regulates pancreatic islet morphogenesis.
- 2009
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In: BMC developmental biology. - 1471-213X. ; 9:2
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Journal article (peer-reviewed)abstract
- BACKGROUND: Pancreatic islets of Langerhans originate from endocrine progenitors within the pancreatic ductal epithelium. Concomitant with differentiation of these progenitors into hormone-producing cells such cells delaminate, aggregate and migrate away from the ductal epithelium. The cellular and molecular mechanisms regulating islet cell delamination and cell migration are poorly understood. Extensive biochemical and cell biological studies using cultured cells demonstrated that Rac1, a member of the Rho family of small GTPases, acts as a key regulator of cell migration. RESULTS: To address the functional role of Rac1 in islet morphogenesis, we generated transgenic mice expressing dominant negative Rac1 under regulation of the Rat Insulin Promoter. Blocking Rac1 function in beta cells inhibited their migration away from the ductal epithelium in vivo. Consistently, transgenic islet cell spreading was compromised in vitro. We also show that the EGF-receptor ligand betacellulin induced actin remodelling and cell spreading in wild-type islets, but not in transgenic islets. Finally, we demonstrate that cell-cell contact E-cadherin increased as a consequence of blocking Rac1 activity. CONCLUSION: Our data support a model where Rac1 signalling controls islet cell migration by modulating E-cadherin-mediated cell-cell adhesion. Furthermore, in vitro experiments show that betacellulin stimulated islet cell spreading and actin remodelling is compromised in transgenic islets, suggesting that betacellulin may act as a regulator of Rac1 activity and islet migration in vivo. Our results further emphasize Rac1 as a key regulator of cell migration and cell adhesion during tissue and organ morphogenesis.
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| 2. |
- Johansson, Jenny, et al.
(author)
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N-cadherin is dispensable for pancreas development but required for beta-cell granule turnover.
- 2010
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In: Genesis: The Journal of Genetics and Development. - : Wiley. - 1526-954X. ; 48:6, s. 374-381
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Journal article (peer-reviewed)abstract
- The cadherin family of cell adhesion molecules mediates adhesive interactions that are required for the formation and maintenance of tissues. Previously, we demonstrated that N-cadherin, which is required for numerous morphogenetic processes, is expressed in the pancreatic epithelium at E9.5, but later becomes restricted to endocrine aggregates in mice. To study the role of N-cadherin during pancreas formation and function we generated a tissue-specific knockout of N-cadherin in the early pancreatic epithelium by inter-crossing N-cadherin-floxed mice with Pdx1Cre mice. Analysis of pancreas-specific ablation of N-cadherin demonstrates that N-cadherin is dispensable for pancreatic development, but required for beta-cell granule turnover. The number of insulin secretory granules is significantly reduced in N-cadherin-deficient beta-cells, and as a consequence insulin secretion is decreased.
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| 3. |
- Kesavan, Gokul
(author)
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Cdc42 and Rac1 in Pancreatic Tubulogenesis and Islet Formation
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Tubes form the basic structure of several organs like lungs, kidneys, glandular organs like the pancreas, mammary and salivary glands. Tube formation involves a series of dynamic and interdependent cellular processes, including cytoskeletal reorganization, assembly of intercellular junctional complexes, and cell polarization. Understanding how cells polarize and coordinate tubulogenesis during organ formation is a central question in biology. Tubulogenesis often coincides with cell lineage specification during organ development. Hence, an elementary question is whether these two processes are independently controlled, or whether proper cell specification depends on formation of tubes. To address these fundamental questions, we have studied the functional role of Cdc42 in pancreatic tubulogenesis. We present evidence that Cdc42 is essential for tube formation, specifically for initiating microlumen formation and later for maintaining apical cell polarity. Finally, we show that Cdc42 controls cell specification non-cell-autonomously by providing the correct microenvironment for proper control of cell fate choices of multipotent progenitors. To understand the process and importance of endocrine cell delamination and migration from the ductal epithelium, we used transgenic mouse models expressing the dominant active Cdc42 (Cdc42 DA) or the dominant negative Rac1 (Rac1 DN) in the insulin cells. Active Cdc42 enhanced E-cadherin and F-actin at the cell-cell contacts and blocked the delamination of newly formed insulin cells. The beta cell numbers were severely reduced and resulted in hyperglycemia. Expression of dominant negative Rac1 did not affect the delamination but impaired the subsequent migration and organization of islet cells. E-cadherin was enhanced in the cell-cell contacts of the transgenic islet cells expressing Rac1 DN. Our results describe the process of tube formation in glandular organs like pancreas and identified key regulators in the process. In addition, we show tube formation plays a crucial role in establishing correct microenvironment for proper cell fate specification. Bo
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| 4. |
- Kesavan, Gokul, et al.
(author)
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Cdc42-mediated tubulogenesis controls cell specification.
- 2009
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In: Cell. - : Elsevier BV. - 1097-4172 .- 0092-8674. ; 139:4, s. 791-801
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Journal article (peer-reviewed)abstract
- Understanding how cells polarize and coordinate tubulogenesis during organ formation is a central question in biology. Tubulogenesis often coincides with cell-lineage specification during organ development. Hence, an elementary question is whether these two processes are independently controlled, or whether proper cell specification depends on formation of tubes. To address these fundamental questions, we have studied the functional role of Cdc42 in pancreatic tubulogenesis. We present evidence that Cdc42 is essential for tube formation, specifically for initiating microlumen formation and later for maintaining apical cell polarity. Finally, we show that Cdc42 controls cell specification non-cell-autonomously by providing the correct microenvironment for proper control of cell-fate choices of multipotent progenitors. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.
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| 5. |
- Kesavan, Gokul, et al.
(author)
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Cdc42/N-WASP signaling links actin dynamics to pancreatic β cell delamination and differentiation.
- 2014
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In: Development: For advances in developmental biology and stem cells. - : The Company of Biologists. - 1477-9129. ; 141:3, s. 685-696
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Journal article (peer-reviewed)abstract
- Delamination plays a pivotal role during normal development and cancer. Previous work has demonstrated that delamination and epithelial cell movement within the plane of an epithelium are associated with a change in cellular phenotype. However, how this positional change is linked to differentiation remains unknown. Using the developing mouse pancreas as a model system, we show that β cell delamination and differentiation are two independent events, which are controlled by Cdc42/N-WASP signaling. Specifically, we show that expression of constitutively active Cdc42 in β cells inhibits β cell delamination and differentiation. These processes are normally associated with junctional actin and cell-cell junction disassembly and the expression of fate-determining transcription factors, such as Isl1 and MafA. Mechanistically, we demonstrate that genetic ablation of N-WASP in β cells expressing constitutively active Cdc42 partially restores both delamination and β cell differentiation. These findings elucidate how junctional actin dynamics via Cdc42/N-WASP signaling cell-autonomously control not only epithelial delamination but also cell differentiation during mammalian organogenesis.
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