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Connexin43 deficiency causes delayed ossification, craniofacial abnormalities, and osteoblast dysfunction.

Lecanda F, Warlow PM, Sheikh S, Furlan F, Steinberg TH, Civitelli R - J. Cell Biol. (2000)

Bottom Line: We have shown that overexpression of Cx45 in osteoblasts expressing endogenous Cx43 leads to decreased cell-cell communication (Koval, M., S.T.Cell to cell diffusion of calcein was poor among Cx43-deficient osteoblasts, whose differentiated phenotypic profile and mineralization potential were greatly impaired, compared with wild-type cells.Cell to cell signaling, mediated by Cx43 gap junctions, was critical for normal osteogenesis, craniofacial development, and osteoblastic function.

View Article: PubMed Central - PubMed

Affiliation: Divisions of Bone and Mineral and Infectious Diseases, Department of Internal Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St. Louis, Missouri 63110, USA.

ABSTRACT
Connexin(Cx)43 is the major gap junction protein present in osteoblasts. We have shown that overexpression of Cx45 in osteoblasts expressing endogenous Cx43 leads to decreased cell-cell communication (Koval, M., S.T. Geist, E.M. Westphale, A.E. Kemendy, R. Civitelli, E.C. Beyer, and T.H. Steinberg. 1995. J. Cell Biol. 130:987-995) and transcriptional downregulation of several osteoblastic differentiation markers (Lecanda, F., D.A. Towler, K. Ziambaras, S.-L. Cheng, M. Koval, T.H. Steinberg, and R. Civitelli. 1998. Mol. Biol. Cell 9:2249-2258). Here, using the Cx43- mouse model, we determined whether genetic deficiency of Cx43 affects skeletal development in vivo. Both intramembranous and endochondral ossification of the cranial vault were delayed in the mutant embryos, and cranial bones originating from migratory neural crest cells were also hypoplastic, leaving an open foramen at birth. Cx43-deficient animals also exhibited retarded ossification of the clavicles, ribs, vertebrae, and limbs, demonstrating that skeletal abnormalities are not restricted to a neural crest defect. However, the axial and appendicular skeleton of Cx43- animals were essentially normal at birth. Cell to cell diffusion of calcein was poor among Cx43-deficient osteoblasts, whose differentiated phenotypic profile and mineralization potential were greatly impaired, compared with wild-type cells. Therefore, in addition to the reported neural crest cell defect, lack of Cx43 also causes a generalized osteoblast dysfunction, leading to delayed mineralization and skull abnormalities. Cell to cell signaling, mediated by Cx43 gap junctions, was critical for normal osteogenesis, craniofacial development, and osteoblastic function.

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Sagittal sections of the (a and b) parietal and (c and d) occipital bones of the (a and c) wild-type and (b and d) Cx43−/− mice stained with safranin/fast green. Note that the parietal bone is thinner and more brittle in the Cx43 homozygous mutants. (d) The cartilaginous anlage of the occipital bone is more prominent in the Cx43−/− animals.
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Figure 4: Sagittal sections of the (a and b) parietal and (c and d) occipital bones of the (a and c) wild-type and (b and d) Cx43−/− mice stained with safranin/fast green. Note that the parietal bone is thinner and more brittle in the Cx43 homozygous mutants. (d) The cartilaginous anlage of the occipital bone is more prominent in the Cx43−/− animals.

Mentions: The lack of proper development of bones forming the roof of the skull, namely the parietal and frontal bones, resulted in an open parietal foramen (Fig. 3, a–d). The much reduced size of parietal and frontal bones, in conjunction with the hypoplastic interparietal bone, resulted in a smaller calvarium and a more flattened skull (Fig. 3, a and b). This is the most prominent phenotypic feature of Cx43−/− mice at birth. Microscopic examination of sagittal sections of the skull of Cx43−/− mice at birth revealed thinner, brittle parietal bones with reduced diploic space in the homozygous mutants compared with control littermates (Fig. 4, a and b). In contrast, homozygous mutants displayed more prominent cartilagenous anlage of the occipital bone (Fig. 4c and Fig. d), presumably the consequence of retarded ossification. We conclude that Cx43 deficiency causes delayed development of all neural crest–derived facial (nasal, maxillary, vomer, palatine, and mandibular) and cranial vault elements (frontal, parietal, and squamosal).


Connexin43 deficiency causes delayed ossification, craniofacial abnormalities, and osteoblast dysfunction.

Lecanda F, Warlow PM, Sheikh S, Furlan F, Steinberg TH, Civitelli R - J. Cell Biol. (2000)

Sagittal sections of the (a and b) parietal and (c and d) occipital bones of the (a and c) wild-type and (b and d) Cx43−/− mice stained with safranin/fast green. Note that the parietal bone is thinner and more brittle in the Cx43 homozygous mutants. (d) The cartilaginous anlage of the occipital bone is more prominent in the Cx43−/− animals.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2169447&req=5

Figure 4: Sagittal sections of the (a and b) parietal and (c and d) occipital bones of the (a and c) wild-type and (b and d) Cx43−/− mice stained with safranin/fast green. Note that the parietal bone is thinner and more brittle in the Cx43 homozygous mutants. (d) The cartilaginous anlage of the occipital bone is more prominent in the Cx43−/− animals.
Mentions: The lack of proper development of bones forming the roof of the skull, namely the parietal and frontal bones, resulted in an open parietal foramen (Fig. 3, a–d). The much reduced size of parietal and frontal bones, in conjunction with the hypoplastic interparietal bone, resulted in a smaller calvarium and a more flattened skull (Fig. 3, a and b). This is the most prominent phenotypic feature of Cx43−/− mice at birth. Microscopic examination of sagittal sections of the skull of Cx43−/− mice at birth revealed thinner, brittle parietal bones with reduced diploic space in the homozygous mutants compared with control littermates (Fig. 4, a and b). In contrast, homozygous mutants displayed more prominent cartilagenous anlage of the occipital bone (Fig. 4c and Fig. d), presumably the consequence of retarded ossification. We conclude that Cx43 deficiency causes delayed development of all neural crest–derived facial (nasal, maxillary, vomer, palatine, and mandibular) and cranial vault elements (frontal, parietal, and squamosal).

Bottom Line: We have shown that overexpression of Cx45 in osteoblasts expressing endogenous Cx43 leads to decreased cell-cell communication (Koval, M., S.T.Cell to cell diffusion of calcein was poor among Cx43-deficient osteoblasts, whose differentiated phenotypic profile and mineralization potential were greatly impaired, compared with wild-type cells.Cell to cell signaling, mediated by Cx43 gap junctions, was critical for normal osteogenesis, craniofacial development, and osteoblastic function.

View Article: PubMed Central - PubMed

Affiliation: Divisions of Bone and Mineral and Infectious Diseases, Department of Internal Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St. Louis, Missouri 63110, USA.

ABSTRACT
Connexin(Cx)43 is the major gap junction protein present in osteoblasts. We have shown that overexpression of Cx45 in osteoblasts expressing endogenous Cx43 leads to decreased cell-cell communication (Koval, M., S.T. Geist, E.M. Westphale, A.E. Kemendy, R. Civitelli, E.C. Beyer, and T.H. Steinberg. 1995. J. Cell Biol. 130:987-995) and transcriptional downregulation of several osteoblastic differentiation markers (Lecanda, F., D.A. Towler, K. Ziambaras, S.-L. Cheng, M. Koval, T.H. Steinberg, and R. Civitelli. 1998. Mol. Biol. Cell 9:2249-2258). Here, using the Cx43- mouse model, we determined whether genetic deficiency of Cx43 affects skeletal development in vivo. Both intramembranous and endochondral ossification of the cranial vault were delayed in the mutant embryos, and cranial bones originating from migratory neural crest cells were also hypoplastic, leaving an open foramen at birth. Cx43-deficient animals also exhibited retarded ossification of the clavicles, ribs, vertebrae, and limbs, demonstrating that skeletal abnormalities are not restricted to a neural crest defect. However, the axial and appendicular skeleton of Cx43- animals were essentially normal at birth. Cell to cell diffusion of calcein was poor among Cx43-deficient osteoblasts, whose differentiated phenotypic profile and mineralization potential were greatly impaired, compared with wild-type cells. Therefore, in addition to the reported neural crest cell defect, lack of Cx43 also causes a generalized osteoblast dysfunction, leading to delayed mineralization and skull abnormalities. Cell to cell signaling, mediated by Cx43 gap junctions, was critical for normal osteogenesis, craniofacial development, and osteoblastic function.

Show MeSH
Related in: MedlinePlus