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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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Phenotypes of wt and plakophilin 2–deficient (pkp2−/−) mutant embryos at E10.75. (a and b) External appearance of embryos. In the mutant embryo, blood has accumulated in the pericardial and peritoneal cavities, which are connected at this embryonal stage (Kaufman and Bard, 1999). (c–f) The vasculature of the yolk sac contains red blood cells in the wt, but not in the pkp2−/− embryos, as shown by whole-mount photography (c and d) and microscopy of hematoxylin- and eosin-stained sections of endothelia (e and f). (g and h) The vasculature of wt and pkp2−/− mutant yolk sacs is intact, as shown by anti-PECAM immunostaining of endothelial cells. (i and j) Light microscopy of toluidine blue–stained transverse sections of embryonic hearts: note the reduced thickness of the atrial walls and the reduced trabeculation of the ventricle, as well as blood accumulation in the pericardial cavity of pkp2−/− mutant hearts (arrow); ra and la, right and left atria; bc and cv, bulbus cordis (future right ventricle) and common ventricle (future left ventricle). (k and l) Higher magnifications of atrial walls in wt and plakophilin 2 −/− mutant hearts. In general, the atrial walls appear thinner in the mutant (l). The position of a possible small leakage site is indicated (arrowhead) in the mutant hearts (l); ed, endocardial cells; ep, epicardial cells; cm, cardiomyocytes; rb, red blood cells. Bars: 1,000 μm (a, b, c, d, g, and h), 100 μm (e and f), 300 μm (i and j), 50 μm (k and l).
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fig2: Phenotypes of wt and plakophilin 2–deficient (pkp2−/−) mutant embryos at E10.75. (a and b) External appearance of embryos. In the mutant embryo, blood has accumulated in the pericardial and peritoneal cavities, which are connected at this embryonal stage (Kaufman and Bard, 1999). (c–f) The vasculature of the yolk sac contains red blood cells in the wt, but not in the pkp2−/− embryos, as shown by whole-mount photography (c and d) and microscopy of hematoxylin- and eosin-stained sections of endothelia (e and f). (g and h) The vasculature of wt and pkp2−/− mutant yolk sacs is intact, as shown by anti-PECAM immunostaining of endothelial cells. (i and j) Light microscopy of toluidine blue–stained transverse sections of embryonic hearts: note the reduced thickness of the atrial walls and the reduced trabeculation of the ventricle, as well as blood accumulation in the pericardial cavity of pkp2−/− mutant hearts (arrow); ra and la, right and left atria; bc and cv, bulbus cordis (future right ventricle) and common ventricle (future left ventricle). (k and l) Higher magnifications of atrial walls in wt and plakophilin 2 −/− mutant hearts. In general, the atrial walls appear thinner in the mutant (l). The position of a possible small leakage site is indicated (arrowhead) in the mutant hearts (l); ed, endocardial cells; ep, epicardial cells; cm, cardiomyocytes; rb, red blood cells. Bars: 1,000 μm (a, b, c, d, g, and h), 100 μm (e and f), 300 μm (i and j), 50 μm (k and l).

Mentions: To determine the cause of lethality in plakophilin 2–deficient mice, we examined embryos at E9.5 and later stages of development. Homozygous embryos at E10.75 were pale in the head and the dorsal trunk region, i.e., blood was not distributed homogenously but had accumulated in the pericardial cavity and also in the peritoneal cavity (Fig. 2, a and b). Similarly, blood was not found in the blood vessels of the yolk sacs of homozygous plakophilin 2 −/− embryos (Fig. 2, c and d; see section through blood vessels in Fig. 2, e and f).The vasculature appeared to be largely intact, as determined by PECAM staining, although some minor alterations in the overall pattern of the blood vessel network could be recognized (Fig. 2, g and h). Transverse sections through the forming heart of the plakophilin 2 mutants at E10.75 showed reduced trabeculation in the heart ventricles (Fig. 2, i and j) and thinner walls of the atria, as in some places two cell layers instead of three to four in the wt embryos were observed (Fig. 2, k and l; see also (Fig. 3 and Sedmera et al., 2000). No alterations in cell proliferation and apoptosis were seen in mutant hearts, as determined by anti-phosphohistone 3 and TUNEL staining (unpublished data). Overt rupture of heart walls, as previously found in plakoglobin-deficient mutant embryos (Ruiz et al., 1996), could not be detected, indicating that blood leakage occurred through small perforations of the beating heart (the position of a possible small leakage site is denoted by an arrowhead in Fig. 2 l). Homozygous embryos of earlier stages (E9.5–E10) did not show blood leakage into the pericard, whereas embryos of E11.5–E12 displayed, in addition to blood leakage, swollen pericardiac and peritoneal cavities, before they became necrotic (unpublished data).


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)

Phenotypes of wt and plakophilin 2–deficient (pkp2−/−) mutant embryos at E10.75. (a and b) External appearance of embryos. In the mutant embryo, blood has accumulated in the pericardial and peritoneal cavities, which are connected at this embryonal stage (Kaufman and Bard, 1999). (c–f) The vasculature of the yolk sac contains red blood cells in the wt, but not in the pkp2−/− embryos, as shown by whole-mount photography (c and d) and microscopy of hematoxylin- and eosin-stained sections of endothelia (e and f). (g and h) The vasculature of wt and pkp2−/− mutant yolk sacs is intact, as shown by anti-PECAM immunostaining of endothelial cells. (i and j) Light microscopy of toluidine blue–stained transverse sections of embryonic hearts: note the reduced thickness of the atrial walls and the reduced trabeculation of the ventricle, as well as blood accumulation in the pericardial cavity of pkp2−/− mutant hearts (arrow); ra and la, right and left atria; bc and cv, bulbus cordis (future right ventricle) and common ventricle (future left ventricle). (k and l) Higher magnifications of atrial walls in wt and plakophilin 2 −/− mutant hearts. In general, the atrial walls appear thinner in the mutant (l). The position of a possible small leakage site is indicated (arrowhead) in the mutant hearts (l); ed, endocardial cells; ep, epicardial cells; cm, cardiomyocytes; rb, red blood cells. Bars: 1,000 μm (a, b, c, d, g, and h), 100 μm (e and f), 300 μm (i and j), 50 μm (k and l).
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fig2: Phenotypes of wt and plakophilin 2–deficient (pkp2−/−) mutant embryos at E10.75. (a and b) External appearance of embryos. In the mutant embryo, blood has accumulated in the pericardial and peritoneal cavities, which are connected at this embryonal stage (Kaufman and Bard, 1999). (c–f) The vasculature of the yolk sac contains red blood cells in the wt, but not in the pkp2−/− embryos, as shown by whole-mount photography (c and d) and microscopy of hematoxylin- and eosin-stained sections of endothelia (e and f). (g and h) The vasculature of wt and pkp2−/− mutant yolk sacs is intact, as shown by anti-PECAM immunostaining of endothelial cells. (i and j) Light microscopy of toluidine blue–stained transverse sections of embryonic hearts: note the reduced thickness of the atrial walls and the reduced trabeculation of the ventricle, as well as blood accumulation in the pericardial cavity of pkp2−/− mutant hearts (arrow); ra and la, right and left atria; bc and cv, bulbus cordis (future right ventricle) and common ventricle (future left ventricle). (k and l) Higher magnifications of atrial walls in wt and plakophilin 2 −/− mutant hearts. In general, the atrial walls appear thinner in the mutant (l). The position of a possible small leakage site is indicated (arrowhead) in the mutant hearts (l); ed, endocardial cells; ep, epicardial cells; cm, cardiomyocytes; rb, red blood cells. Bars: 1,000 μm (a, b, c, d, g, and h), 100 μm (e and f), 300 μm (i and j), 50 μm (k and l).
Mentions: To determine the cause of lethality in plakophilin 2–deficient mice, we examined embryos at E9.5 and later stages of development. Homozygous embryos at E10.75 were pale in the head and the dorsal trunk region, i.e., blood was not distributed homogenously but had accumulated in the pericardial cavity and also in the peritoneal cavity (Fig. 2, a and b). Similarly, blood was not found in the blood vessels of the yolk sacs of homozygous plakophilin 2 −/− embryos (Fig. 2, c and d; see section through blood vessels in Fig. 2, e and f).The vasculature appeared to be largely intact, as determined by PECAM staining, although some minor alterations in the overall pattern of the blood vessel network could be recognized (Fig. 2, g and h). Transverse sections through the forming heart of the plakophilin 2 mutants at E10.75 showed reduced trabeculation in the heart ventricles (Fig. 2, i and j) and thinner walls of the atria, as in some places two cell layers instead of three to four in the wt embryos were observed (Fig. 2, k and l; see also (Fig. 3 and Sedmera et al., 2000). No alterations in cell proliferation and apoptosis were seen in mutant hearts, as determined by anti-phosphohistone 3 and TUNEL staining (unpublished data). Overt rupture of heart walls, as previously found in plakoglobin-deficient mutant embryos (Ruiz et al., 1996), could not be detected, indicating that blood leakage occurred through small perforations of the beating heart (the position of a possible small leakage site is denoted by an arrowhead in Fig. 2 l). Homozygous embryos of earlier stages (E9.5–E10) did not show blood leakage into the pericard, whereas embryos of E11.5–E12 displayed, in addition to blood leakage, swollen pericardiac and peritoneal cavities, before they became necrotic (unpublished data).

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