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Neural cell adhesion molecule (N-CAM) is required for cell type segregation and normal ultrastructure in pancreatic islets.

Esni F, Täljedal IB, Perl AK, Cremer H, Christofori G, Semb H - J. Cell Biol. (1999)

Bottom Line: These data together with the polarized distribution of islet cell nuclei and Na+/K+-ATPase indicate that islet cell polarity is also affected.Finally, degranulation of beta cells suggests that N-CAM is required for normal turnover of insulin-containing secretory granules.Taken together, our results confirm in vivo the hypothesis that a cell adhesion molecule, in this case N-CAM, is required for cell type segregation during organogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Umeå University, S-901 87 Umeå, Sweden.

ABSTRACT
Classical cell dissociation/reaggregation experiments with embryonic tissue and cultured cells have established that cellular cohesiveness, mediated by cell adhesion molecules, is important in determining the organization of cells within tissue and organs. We have employed N-CAM-deficient mice to determine whether N-CAM plays a functional role in the proper segregation of cells during the development of islets of Langerhans. In N-CAM-deficient mice the normal localization of glucagon-producing alpha cells in the periphery of pancreatic islets is lost, resulting in a more randomized cell distribution. In contrast to the expected reduction of cell-cell adhesion in N-CAM-deficient mice, a significant increase in the clustering of cadherins, F-actin, and cell-cell junctions is observed suggesting enhanced cadherin-mediated adhesion in the absence of proper N-CAM function. These data together with the polarized distribution of islet cell nuclei and Na+/K+-ATPase indicate that islet cell polarity is also affected. Finally, degranulation of beta cells suggests that N-CAM is required for normal turnover of insulin-containing secretory granules. Taken together, our results confirm in vivo the hypothesis that a cell adhesion molecule, in this case N-CAM, is required for cell type segregation during organogenesis. Possible mechanisms underlying this phenomenon may include changes in cadherin-mediated adhesion and cell polarity.

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Subcellular organization of N-cadherin and F-actin  is altered in pancreatic islets of  N-CAM mutant mice. (a–d)  Immunofluorescence stainings  of sections from adult control  (a, +/+), N-CAM +/− (b, +/−),  and N-CAM −/− (c and d, −/−)  pancreata with anti-N-cadherin  mAb. Inset in d shows E-cadherin distribution in an exocrine acinus. (e–h) Staining of  F-actin on sections from adult  control (e, +/+), N-CAM +/−  (f, +/−), and N-CAM −/− (g  and h, −/−) pancreata with  rhodamine-phalloidin. Inset in  h shows F-actin distribution  in an exocrine acinus. Arrows  indicate rosette-like structures,  or endocrine acini. The subcellular localization of N-cadherin  and F-actin is reminiscent of  the distribution of E-cadherin  and F-actin in exocrine acini.  Bars, 10 μm.
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Figure 4: Subcellular organization of N-cadherin and F-actin is altered in pancreatic islets of N-CAM mutant mice. (a–d) Immunofluorescence stainings of sections from adult control (a, +/+), N-CAM +/− (b, +/−), and N-CAM −/− (c and d, −/−) pancreata with anti-N-cadherin mAb. Inset in d shows E-cadherin distribution in an exocrine acinus. (e–h) Staining of F-actin on sections from adult control (e, +/+), N-CAM +/− (f, +/−), and N-CAM −/− (g and h, −/−) pancreata with rhodamine-phalloidin. Inset in h shows F-actin distribution in an exocrine acinus. Arrows indicate rosette-like structures, or endocrine acini. The subcellular localization of N-cadherin and F-actin is reminiscent of the distribution of E-cadherin and F-actin in exocrine acini. Bars, 10 μm.

Mentions: To elucidate the molecular mechanisms behind the altered cell type segregation within islets of Langerhans in N-CAM-deficient mice, the subcellular distribution of molecules that are known to affect morphogenetic behaviors of cells or act as molecular markers for cell polarity were examined. Thus far, three members of the classic cadherins have been found to be expressed in islets, E-, N-, and R-cadherin (Begemann et al., 1990; Moller et al., 1992; Hutton et al., 1993; Dahl et al., 1996; Esni, F., and H. Semb, unpublished observations). Only N-cadherin and E-cadherin localize to cell–cell contacts (Begemann et al., 1990; Dahl et al., 1996), whereas R-cadherin distribute mainly in the cytoplasm (Dahl, U., F. Esni, and H. Semb, unpublished observations). Analysis of N-CAM-deficient mice revealed striking changes in the subcellular distribution of N-cadherin and E-cadherin, whereas R-cadherin was unaffected. As mentioned previously, these cadherins normally localize to all regions engaged in cell–cell adhesion without any apparent clustering (Begemann et al., 1990; Dahl et al., 1996; Fig. 4 a). In N-CAM-deficient mice, N-cadherin (Fig. 4, a–d) but also E-cadherin (data not shown) accumulate in discrete regions of cell–cell contacts, suggesting that N-CAM prevents clustering of cadherins within islets of Langerhans in control mice. Because cadherins are capable of affecting cortical F-actin organization and cell polarity, the subcellular distribution of F-actin and Na+/K+-ATPase (Hammerton et al., 1991; Drubin and Nelson, 1996), apical and basolateral epithelial cell polarity markers, respectively, were investigated in N-CAM-deficient mice. In control islets F-actin's preferential distribution is adjacent to cell–cell contacts (Fig. 4 e), whereas in N-CAM-deficient mice it accumulates together with the cadherins (Fig. 4, f–h). The visualization of the redistribution of N-cadherin, E-cadherin, and F-actin appears as multicellular rosette structures, which are composed of all endocrine cell types, and are reminiscent of the apical enrichment of E-cadherin and F-actin in exocrine acinar cells (insets in Fig. 4, d and h). We propose to refer to these structures as endocrine acini. The striking changes in the organization of cadherins and actin filaments in islets of N-CAM-deficient mice suggest that cell polarity may also be affected. In further support for alterations in islet cell polarity, the subcellular localization of the basolateral epithelial cell polarity marker Na+/K+-ATPase and the nuclei within islets of N-CAM-deficient is reminiscent of their distribution within fully polarized exocrine acinar cells (Fig. 5, compare a with c and d, and e with g and h). In normal control islets, Na+/ K+-ATPase colocalizes with N-cadherin and E-cadherin in cell contact regions (Fig. 5 b, and data not shown), whereas in islets of N-CAM-deficient mice Na+/K+-ATPase does not accumulate in regions with increased cadherin and F-actin clustering (Fig. 5, c and d). Furthermore, while islet cell nuclei are randomly distributed in control islets (Fig. 5 f), cell nuclei are preferentially localized to the basal regions of those islet cells that are organized in endocrine acini in N-CAM-deficient mice (Fig. 5, g and h). Similar to the effect on cell type segregation, changes in the subcellular localization of cadherins and F-actin in N-CAM-deficient mice were first observed at 4–5 wk of age. To examine whether transdifferentiation of endocrine cells into exocrine acinar cells could explain the appearance of the endocrine acinar structures, expression of acinar markers, such as amylase or carboxypeptidase, was investigated. However, none of these exocrine markers is expressed in islets of N-CAM +/− and N-CAM −/− mice, indicating that the appearance of acinar structures in islets of Langerhans does not resemble a transdifferentiation process (data not shown).


Neural cell adhesion molecule (N-CAM) is required for cell type segregation and normal ultrastructure in pancreatic islets.

Esni F, Täljedal IB, Perl AK, Cremer H, Christofori G, Semb H - J. Cell Biol. (1999)

Subcellular organization of N-cadherin and F-actin  is altered in pancreatic islets of  N-CAM mutant mice. (a–d)  Immunofluorescence stainings  of sections from adult control  (a, +/+), N-CAM +/− (b, +/−),  and N-CAM −/− (c and d, −/−)  pancreata with anti-N-cadherin  mAb. Inset in d shows E-cadherin distribution in an exocrine acinus. (e–h) Staining of  F-actin on sections from adult  control (e, +/+), N-CAM +/−  (f, +/−), and N-CAM −/− (g  and h, −/−) pancreata with  rhodamine-phalloidin. Inset in  h shows F-actin distribution  in an exocrine acinus. Arrows  indicate rosette-like structures,  or endocrine acini. The subcellular localization of N-cadherin  and F-actin is reminiscent of  the distribution of E-cadherin  and F-actin in exocrine acini.  Bars, 10 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2132899&req=5

Figure 4: Subcellular organization of N-cadherin and F-actin is altered in pancreatic islets of N-CAM mutant mice. (a–d) Immunofluorescence stainings of sections from adult control (a, +/+), N-CAM +/− (b, +/−), and N-CAM −/− (c and d, −/−) pancreata with anti-N-cadherin mAb. Inset in d shows E-cadherin distribution in an exocrine acinus. (e–h) Staining of F-actin on sections from adult control (e, +/+), N-CAM +/− (f, +/−), and N-CAM −/− (g and h, −/−) pancreata with rhodamine-phalloidin. Inset in h shows F-actin distribution in an exocrine acinus. Arrows indicate rosette-like structures, or endocrine acini. The subcellular localization of N-cadherin and F-actin is reminiscent of the distribution of E-cadherin and F-actin in exocrine acini. Bars, 10 μm.
Mentions: To elucidate the molecular mechanisms behind the altered cell type segregation within islets of Langerhans in N-CAM-deficient mice, the subcellular distribution of molecules that are known to affect morphogenetic behaviors of cells or act as molecular markers for cell polarity were examined. Thus far, three members of the classic cadherins have been found to be expressed in islets, E-, N-, and R-cadherin (Begemann et al., 1990; Moller et al., 1992; Hutton et al., 1993; Dahl et al., 1996; Esni, F., and H. Semb, unpublished observations). Only N-cadherin and E-cadherin localize to cell–cell contacts (Begemann et al., 1990; Dahl et al., 1996), whereas R-cadherin distribute mainly in the cytoplasm (Dahl, U., F. Esni, and H. Semb, unpublished observations). Analysis of N-CAM-deficient mice revealed striking changes in the subcellular distribution of N-cadherin and E-cadherin, whereas R-cadherin was unaffected. As mentioned previously, these cadherins normally localize to all regions engaged in cell–cell adhesion without any apparent clustering (Begemann et al., 1990; Dahl et al., 1996; Fig. 4 a). In N-CAM-deficient mice, N-cadherin (Fig. 4, a–d) but also E-cadherin (data not shown) accumulate in discrete regions of cell–cell contacts, suggesting that N-CAM prevents clustering of cadherins within islets of Langerhans in control mice. Because cadherins are capable of affecting cortical F-actin organization and cell polarity, the subcellular distribution of F-actin and Na+/K+-ATPase (Hammerton et al., 1991; Drubin and Nelson, 1996), apical and basolateral epithelial cell polarity markers, respectively, were investigated in N-CAM-deficient mice. In control islets F-actin's preferential distribution is adjacent to cell–cell contacts (Fig. 4 e), whereas in N-CAM-deficient mice it accumulates together with the cadherins (Fig. 4, f–h). The visualization of the redistribution of N-cadherin, E-cadherin, and F-actin appears as multicellular rosette structures, which are composed of all endocrine cell types, and are reminiscent of the apical enrichment of E-cadherin and F-actin in exocrine acinar cells (insets in Fig. 4, d and h). We propose to refer to these structures as endocrine acini. The striking changes in the organization of cadherins and actin filaments in islets of N-CAM-deficient mice suggest that cell polarity may also be affected. In further support for alterations in islet cell polarity, the subcellular localization of the basolateral epithelial cell polarity marker Na+/K+-ATPase and the nuclei within islets of N-CAM-deficient is reminiscent of their distribution within fully polarized exocrine acinar cells (Fig. 5, compare a with c and d, and e with g and h). In normal control islets, Na+/ K+-ATPase colocalizes with N-cadherin and E-cadherin in cell contact regions (Fig. 5 b, and data not shown), whereas in islets of N-CAM-deficient mice Na+/K+-ATPase does not accumulate in regions with increased cadherin and F-actin clustering (Fig. 5, c and d). Furthermore, while islet cell nuclei are randomly distributed in control islets (Fig. 5 f), cell nuclei are preferentially localized to the basal regions of those islet cells that are organized in endocrine acini in N-CAM-deficient mice (Fig. 5, g and h). Similar to the effect on cell type segregation, changes in the subcellular localization of cadherins and F-actin in N-CAM-deficient mice were first observed at 4–5 wk of age. To examine whether transdifferentiation of endocrine cells into exocrine acinar cells could explain the appearance of the endocrine acinar structures, expression of acinar markers, such as amylase or carboxypeptidase, was investigated. However, none of these exocrine markers is expressed in islets of N-CAM +/− and N-CAM −/− mice, indicating that the appearance of acinar structures in islets of Langerhans does not resemble a transdifferentiation process (data not shown).

Bottom Line: These data together with the polarized distribution of islet cell nuclei and Na+/K+-ATPase indicate that islet cell polarity is also affected.Finally, degranulation of beta cells suggests that N-CAM is required for normal turnover of insulin-containing secretory granules.Taken together, our results confirm in vivo the hypothesis that a cell adhesion molecule, in this case N-CAM, is required for cell type segregation during organogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Umeå University, S-901 87 Umeå, Sweden.

ABSTRACT
Classical cell dissociation/reaggregation experiments with embryonic tissue and cultured cells have established that cellular cohesiveness, mediated by cell adhesion molecules, is important in determining the organization of cells within tissue and organs. We have employed N-CAM-deficient mice to determine whether N-CAM plays a functional role in the proper segregation of cells during the development of islets of Langerhans. In N-CAM-deficient mice the normal localization of glucagon-producing alpha cells in the periphery of pancreatic islets is lost, resulting in a more randomized cell distribution. In contrast to the expected reduction of cell-cell adhesion in N-CAM-deficient mice, a significant increase in the clustering of cadherins, F-actin, and cell-cell junctions is observed suggesting enhanced cadherin-mediated adhesion in the absence of proper N-CAM function. These data together with the polarized distribution of islet cell nuclei and Na+/K+-ATPase indicate that islet cell polarity is also affected. Finally, degranulation of beta cells suggests that N-CAM is required for normal turnover of insulin-containing secretory granules. Taken together, our results confirm in vivo the hypothesis that a cell adhesion molecule, in this case N-CAM, is required for cell type segregation during organogenesis. Possible mechanisms underlying this phenomenon may include changes in cadherin-mediated adhesion and cell polarity.

Show MeSH
Related in: MedlinePlus