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Requirement of plakophilin 2 for heart morphogenesis and cardiac junction formation.

Grossmann KS, Grund C, Huelsken J, Behrend M, Erdmann B, Franke WW, Birchmeier W - J. Cell Biol. (2004)

Bottom Line: Plakophilins are proteins of the armadillo family that function in embryonic development and in the adult, and when mutated can cause disease.By contrast, embryonic epithelia show normal junctions.Thus, we conclude that plakophilin 2 is important for the assembly of junctional proteins and represents an essential morphogenic factor and architectural component of the heart.

View Article: PubMed Central - PubMed

Affiliation: Max Delbrueck Center for Molecular Medicine (MDC), D-13092 Berlin, Germany.

ABSTRACT
Plakophilins are proteins of the armadillo family that function in embryonic development and in the adult, and when mutated can cause disease. We have ablated the plakophilin 2 gene in mice. The resulting mutant mice exhibit lethal alterations in heart morphogenesis and stability at mid-gestation (E10.5-E11), characterized by reduced trabeculation, disarrayed cytoskeleton, ruptures of cardiac walls, and blood leakage into the pericardiac cavity. In the absence of plakophilin 2, the cytoskeletal linker protein desmoplakin dissociates from the plaques of the adhering junctions that connect the cardiomyocytes and forms granular aggregates in the cytoplasm. By contrast, embryonic epithelia show normal junctions. Thus, we conclude that plakophilin 2 is important for the assembly of junctional proteins and represents an essential morphogenic factor and architectural component of the heart.

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Dissociation of desmoplakin from the cardiac adhering junctions (areae compositae) in the absence of plakophilin 2. Electron (a and b) and immunoelectron (c–l) microscopy of ultrathin sections through intercalated disk junctions that connect cardiomyocytes of forming hearts in wt and plakophilin 2–deficient (pkp2−/−) E10.75 embryos. Desmosome-like structures (an example is seen in the top part of a) are not seen in the pkp2−/− embryos (b). Although the electron microscopic appearance of plaque-bearing junctions of the fascia adhaerens type is similar in both the wt and the mutant embryos (bottom part of a and b), the localization of desmoplakin (DP), as seen in immunoelectron micrographs (c–g, i, and j), is drastically altered: in the wt embryos, desmoplakin immunogold label is enriched in plaques of both morphotypes of adhering junctions (c and e), usually with higher label intensity at desmosome-like structures (e, compare the right hand junction with the fascia adhaerens–like junction in the left), including “fused” junctions with a practically continuous DP positivity (g). The same localization is seen for plakophilin 2 immunolabel in the wt hearts (h). By contrast, the pkp2−/− embryos show no desmoplakin enrichment at junctional plaques. Instead, DP label is dispersed over the cytoplasm, showing no significant enrichment at plaques (d and f), and is markedly enriched in dense granular aggregates of various sizes occurring throughout the cytoplasm, where they are interspersed between myofibrillar bundles (i) or in close association with loose arrays of IFs (j, for higher magnification see the inset). In contrast, other constituent proteins of these junctions are detected at comparable intensity in both wt and pkp2−/− embryos (k and l present the comparison for N-cadherin). Bars: 1 μm (b), 0.5 mm (a, c–g, i, and j), 0.2 μm (h, k, and l), and 0.1 mm (j, inset). Asterisk marks a cell junction devoid of desmoplakin.
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fig5: Dissociation of desmoplakin from the cardiac adhering junctions (areae compositae) in the absence of plakophilin 2. Electron (a and b) and immunoelectron (c–l) microscopy of ultrathin sections through intercalated disk junctions that connect cardiomyocytes of forming hearts in wt and plakophilin 2–deficient (pkp2−/−) E10.75 embryos. Desmosome-like structures (an example is seen in the top part of a) are not seen in the pkp2−/− embryos (b). Although the electron microscopic appearance of plaque-bearing junctions of the fascia adhaerens type is similar in both the wt and the mutant embryos (bottom part of a and b), the localization of desmoplakin (DP), as seen in immunoelectron micrographs (c–g, i, and j), is drastically altered: in the wt embryos, desmoplakin immunogold label is enriched in plaques of both morphotypes of adhering junctions (c and e), usually with higher label intensity at desmosome-like structures (e, compare the right hand junction with the fascia adhaerens–like junction in the left), including “fused” junctions with a practically continuous DP positivity (g). The same localization is seen for plakophilin 2 immunolabel in the wt hearts (h). By contrast, the pkp2−/− embryos show no desmoplakin enrichment at junctional plaques. Instead, DP label is dispersed over the cytoplasm, showing no significant enrichment at plaques (d and f), and is markedly enriched in dense granular aggregates of various sizes occurring throughout the cytoplasm, where they are interspersed between myofibrillar bundles (i) or in close association with loose arrays of IFs (j, for higher magnification see the inset). In contrast, other constituent proteins of these junctions are detected at comparable intensity in both wt and pkp2−/− embryos (k and l present the comparison for N-cadherin). Bars: 1 μm (b), 0.5 mm (a, c–g, i, and j), 0.2 μm (h, k, and l), and 0.1 mm (j, inset). Asterisk marks a cell junction devoid of desmoplakin.

Mentions: Electron microscopy showed that throughout mid-gestation, the cardiomyocytes of the wt embryos were connected by well-organized intercalated disks that were rich in both types of adhering junctions, the fascia adhaerens–like and the desmosome-like subforms (Fig. 5 a). In the hearts of plakophilin 2 −/− mutants, these two morphotypes of adhering junctions were difficult to distinguish (Fig. 5 b). Electron microscopy and immunogold labeling of wt hearts demonstrated that desmoplakin was located in the plaques of both the desmosome-like and fascia adhaerens–type junctions (Fig. 5, c, e, and g), confirming previous observations (Borrmann, 2000), although a somewhat higher intensity of labeling was generally seen in the more desmosome-like junctions (Fig. 5 e, compare right-hand with left-hand junction). “Fused” type junctions with continuous desmoplakin or plakophilin 2 labeling were also consistently observed in wt hearts (Fig. 5, g and h). Both morphotypes of adhering junctions were also strongly positive for the major transmembrane glycoprotein, N-cadherin (Fig. 5 k).


Requirement of plakophilin 2 for heart morphogenesis and cardiac junction formation.

Grossmann KS, Grund C, Huelsken J, Behrend M, Erdmann B, Franke WW, Birchmeier W - J. Cell Biol. (2004)

Dissociation of desmoplakin from the cardiac adhering junctions (areae compositae) in the absence of plakophilin 2. Electron (a and b) and immunoelectron (c–l) microscopy of ultrathin sections through intercalated disk junctions that connect cardiomyocytes of forming hearts in wt and plakophilin 2–deficient (pkp2−/−) E10.75 embryos. Desmosome-like structures (an example is seen in the top part of a) are not seen in the pkp2−/− embryos (b). Although the electron microscopic appearance of plaque-bearing junctions of the fascia adhaerens type is similar in both the wt and the mutant embryos (bottom part of a and b), the localization of desmoplakin (DP), as seen in immunoelectron micrographs (c–g, i, and j), is drastically altered: in the wt embryos, desmoplakin immunogold label is enriched in plaques of both morphotypes of adhering junctions (c and e), usually with higher label intensity at desmosome-like structures (e, compare the right hand junction with the fascia adhaerens–like junction in the left), including “fused” junctions with a practically continuous DP positivity (g). The same localization is seen for plakophilin 2 immunolabel in the wt hearts (h). By contrast, the pkp2−/− embryos show no desmoplakin enrichment at junctional plaques. Instead, DP label is dispersed over the cytoplasm, showing no significant enrichment at plaques (d and f), and is markedly enriched in dense granular aggregates of various sizes occurring throughout the cytoplasm, where they are interspersed between myofibrillar bundles (i) or in close association with loose arrays of IFs (j, for higher magnification see the inset). In contrast, other constituent proteins of these junctions are detected at comparable intensity in both wt and pkp2−/− embryos (k and l present the comparison for N-cadherin). Bars: 1 μm (b), 0.5 mm (a, c–g, i, and j), 0.2 μm (h, k, and l), and 0.1 mm (j, inset). Asterisk marks a cell junction devoid of desmoplakin.
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fig5: Dissociation of desmoplakin from the cardiac adhering junctions (areae compositae) in the absence of plakophilin 2. Electron (a and b) and immunoelectron (c–l) microscopy of ultrathin sections through intercalated disk junctions that connect cardiomyocytes of forming hearts in wt and plakophilin 2–deficient (pkp2−/−) E10.75 embryos. Desmosome-like structures (an example is seen in the top part of a) are not seen in the pkp2−/− embryos (b). Although the electron microscopic appearance of plaque-bearing junctions of the fascia adhaerens type is similar in both the wt and the mutant embryos (bottom part of a and b), the localization of desmoplakin (DP), as seen in immunoelectron micrographs (c–g, i, and j), is drastically altered: in the wt embryos, desmoplakin immunogold label is enriched in plaques of both morphotypes of adhering junctions (c and e), usually with higher label intensity at desmosome-like structures (e, compare the right hand junction with the fascia adhaerens–like junction in the left), including “fused” junctions with a practically continuous DP positivity (g). The same localization is seen for plakophilin 2 immunolabel in the wt hearts (h). By contrast, the pkp2−/− embryos show no desmoplakin enrichment at junctional plaques. Instead, DP label is dispersed over the cytoplasm, showing no significant enrichment at plaques (d and f), and is markedly enriched in dense granular aggregates of various sizes occurring throughout the cytoplasm, where they are interspersed between myofibrillar bundles (i) or in close association with loose arrays of IFs (j, for higher magnification see the inset). In contrast, other constituent proteins of these junctions are detected at comparable intensity in both wt and pkp2−/− embryos (k and l present the comparison for N-cadherin). Bars: 1 μm (b), 0.5 mm (a, c–g, i, and j), 0.2 μm (h, k, and l), and 0.1 mm (j, inset). Asterisk marks a cell junction devoid of desmoplakin.
Mentions: Electron microscopy showed that throughout mid-gestation, the cardiomyocytes of the wt embryos were connected by well-organized intercalated disks that were rich in both types of adhering junctions, the fascia adhaerens–like and the desmosome-like subforms (Fig. 5 a). In the hearts of plakophilin 2 −/− mutants, these two morphotypes of adhering junctions were difficult to distinguish (Fig. 5 b). Electron microscopy and immunogold labeling of wt hearts demonstrated that desmoplakin was located in the plaques of both the desmosome-like and fascia adhaerens–type junctions (Fig. 5, c, e, and g), confirming previous observations (Borrmann, 2000), although a somewhat higher intensity of labeling was generally seen in the more desmosome-like junctions (Fig. 5 e, compare right-hand with left-hand junction). “Fused” type junctions with continuous desmoplakin or plakophilin 2 labeling were also consistently observed in wt hearts (Fig. 5, g and h). Both morphotypes of adhering junctions were also strongly positive for the major transmembrane glycoprotein, N-cadherin (Fig. 5 k).

Bottom Line: Plakophilins are proteins of the armadillo family that function in embryonic development and in the adult, and when mutated can cause disease.By contrast, embryonic epithelia show normal junctions.Thus, we conclude that plakophilin 2 is important for the assembly of junctional proteins and represents an essential morphogenic factor and architectural component of the heart.

View Article: PubMed Central - PubMed

Affiliation: Max Delbrueck Center for Molecular Medicine (MDC), D-13092 Berlin, Germany.

ABSTRACT
Plakophilins are proteins of the armadillo family that function in embryonic development and in the adult, and when mutated can cause disease. We have ablated the plakophilin 2 gene in mice. The resulting mutant mice exhibit lethal alterations in heart morphogenesis and stability at mid-gestation (E10.5-E11), characterized by reduced trabeculation, disarrayed cytoskeleton, ruptures of cardiac walls, and blood leakage into the pericardiac cavity. In the absence of plakophilin 2, the cytoskeletal linker protein desmoplakin dissociates from the plaques of the adhering junctions that connect the cardiomyocytes and forms granular aggregates in the cytoplasm. By contrast, embryonic epithelia show normal junctions. Thus, we conclude that plakophilin 2 is important for the assembly of junctional proteins and represents an essential morphogenic factor and architectural component of the heart.

Show MeSH
Related in: MedlinePlus