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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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Distribution of glucagon-producing α cells in pancreatic islets of control and N-CAM-deficient mice. Immunofluorescence staining of adult control (a, +/+), N-CAM +/− (b, +/−),  and N-CAM −/− (c, −/−) mice with polyclonal antibodies  against glucagon. In control animals the majority of α cells are localized in the periphery of islets. However, in N-CAM +/− and  N-CAM −/− mice the α cells become more randomly distributed  within the islets, referred to as mixed islets in Table I. Bar, 20 μm.
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Figure 3: Distribution of glucagon-producing α cells in pancreatic islets of control and N-CAM-deficient mice. Immunofluorescence staining of adult control (a, +/+), N-CAM +/− (b, +/−), and N-CAM −/− (c, −/−) mice with polyclonal antibodies against glucagon. In control animals the majority of α cells are localized in the periphery of islets. However, in N-CAM +/− and N-CAM −/− mice the α cells become more randomly distributed within the islets, referred to as mixed islets in Table I. Bar, 20 μm.

Mentions: In the mouse, islets begin to form around 17.5–18 days postcoitum (dpc; Herrera et al., 1991). Already at this stage the islets begin to adopt their final cell organization, i.e., β cells in the center and non-β cells in the periphery. However, the segregation of these cell types is not yet complete and in many aggregates the cells are more or less intermixed. In fact, by using the distribution of glucagon-producing α cells as the criterion of cell type segregation after birth, it was noted that it is not until 4–5 wk of age that the majority of mouse islets adopt their final cell configuration (data not shown). This cell architecture is maintained at least up to 11 mo of age, which is the oldest age that we have analyzed. To investigate whether N-CAM has any influence on islet cell type segregation we compared the ratio of normal and mixed islets between control and N-CAM-deficient mice. We defined normal islets as islets with all α cells distributed within the three most peripheral cell layers and mixed islets as islets, which contain one or more α cells positioned centrally to the three most peripheral cell layers. Although mixed islets were found in control mice (22%), the majority of the islets was defined as normal (78%; Table I, Fig. 3). However, in N-CAM- deficient mice the ratio of normal and mixed islets completely changed. In these mice the number of normal islets were diminished, whereas the majority of the islets was defined as mixed (71% +/−, 67% −/− vs. 22% +/+; Table I, Fig. 3). This effect becomes apparent only when islet cell type segregation is usually complete, i.e., around 4–5 wk of age. In further support of N-CAM's involvement in islet cell type segregation, the extent of inter-mixing of cells within mixed islets of N-CAM-deficient mice was markedly higher as compared with the few mixed islets of control mice. Thus, the percentage of α cells positioned centrally to the three most peripheral cell layers was significantly higher in N-CAM-deficient animals than in control mice (20 +/−, 21 −/− vs. 14 +/+; Table I). Taken together these data suggest that N-CAM regulate cell type segregation during the development of islet of Langerhans. There are, however, several potential explanations for these observations. Either the number of islet cells has changed, or the segregation of islet cells is affected in N-CAM-deficient mice. However, the fact that the number of α cells and pancreatic insulin and glucagon levels exhibits no marked difference between the different genotype mice (Table I and II), suggests that N-CAM is, indeed, a key regulator of islet cell sorting. Besides α cells and β cells, islets consist of two other endocrine cell types, somatostatin-producing D cells and pancreatic polypeptide-producing PP cells. Similarly to α, D, and PP cells are also preferentially confined to the outer rim of islets in control mice, however, to a much lower degree. Their distribution was not detectably affected in N-CAM mutant mice (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)

Distribution of glucagon-producing α cells in pancreatic islets of control and N-CAM-deficient mice. Immunofluorescence staining of adult control (a, +/+), N-CAM +/− (b, +/−),  and N-CAM −/− (c, −/−) mice with polyclonal antibodies  against glucagon. In control animals the majority of α cells are localized in the periphery of islets. However, in N-CAM +/− and  N-CAM −/− mice the α cells become more randomly distributed  within the islets, referred to as mixed islets in Table I. Bar, 20 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2132899&req=5

Figure 3: Distribution of glucagon-producing α cells in pancreatic islets of control and N-CAM-deficient mice. Immunofluorescence staining of adult control (a, +/+), N-CAM +/− (b, +/−), and N-CAM −/− (c, −/−) mice with polyclonal antibodies against glucagon. In control animals the majority of α cells are localized in the periphery of islets. However, in N-CAM +/− and N-CAM −/− mice the α cells become more randomly distributed within the islets, referred to as mixed islets in Table I. Bar, 20 μm.
Mentions: In the mouse, islets begin to form around 17.5–18 days postcoitum (dpc; Herrera et al., 1991). Already at this stage the islets begin to adopt their final cell organization, i.e., β cells in the center and non-β cells in the periphery. However, the segregation of these cell types is not yet complete and in many aggregates the cells are more or less intermixed. In fact, by using the distribution of glucagon-producing α cells as the criterion of cell type segregation after birth, it was noted that it is not until 4–5 wk of age that the majority of mouse islets adopt their final cell configuration (data not shown). This cell architecture is maintained at least up to 11 mo of age, which is the oldest age that we have analyzed. To investigate whether N-CAM has any influence on islet cell type segregation we compared the ratio of normal and mixed islets between control and N-CAM-deficient mice. We defined normal islets as islets with all α cells distributed within the three most peripheral cell layers and mixed islets as islets, which contain one or more α cells positioned centrally to the three most peripheral cell layers. Although mixed islets were found in control mice (22%), the majority of the islets was defined as normal (78%; Table I, Fig. 3). However, in N-CAM- deficient mice the ratio of normal and mixed islets completely changed. In these mice the number of normal islets were diminished, whereas the majority of the islets was defined as mixed (71% +/−, 67% −/− vs. 22% +/+; Table I, Fig. 3). This effect becomes apparent only when islet cell type segregation is usually complete, i.e., around 4–5 wk of age. In further support of N-CAM's involvement in islet cell type segregation, the extent of inter-mixing of cells within mixed islets of N-CAM-deficient mice was markedly higher as compared with the few mixed islets of control mice. Thus, the percentage of α cells positioned centrally to the three most peripheral cell layers was significantly higher in N-CAM-deficient animals than in control mice (20 +/−, 21 −/− vs. 14 +/+; Table I). Taken together these data suggest that N-CAM regulate cell type segregation during the development of islet of Langerhans. There are, however, several potential explanations for these observations. Either the number of islet cells has changed, or the segregation of islet cells is affected in N-CAM-deficient mice. However, the fact that the number of α cells and pancreatic insulin and glucagon levels exhibits no marked difference between the different genotype mice (Table I and II), suggests that N-CAM is, indeed, a key regulator of islet cell sorting. Besides α cells and β cells, islets consist of two other endocrine cell types, somatostatin-producing D cells and pancreatic polypeptide-producing PP cells. Similarly to α, D, and PP cells are also preferentially confined to the outer rim of islets in control mice, however, to a much lower degree. Their distribution was not detectably affected in N-CAM mutant mice (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