Limits...
The high mobility group transcription factor Sox8 is a negative regulator of osteoblast differentiation.

Schmidt K, Schinke T, Haberland M, Priemel M, Schilling AF, Mueldner C, Rueger JM, Sock E, Wegner M, Amling M - J. Cell Biol. (2005)

Bottom Line: This is achieved through a balanced activity of bone-resorbing osteoclasts and bone-forming osteoblasts.In this study, we identify the high mobility group transcription factor Sox8 as a physiologic regulator of bone formation.Together, these data demonstrate a novel function of Sox8, whose tightly controlled expression is critical for bone formation.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biochemistry, Friedrich-Alexander-University, Erlangen-Nürnberg, Erlangen 91054, Germany.

ABSTRACT
Bone remodeling is an important physiologic process that is required to maintain a constant bone mass. This is achieved through a balanced activity of bone-resorbing osteoclasts and bone-forming osteoblasts. In this study, we identify the high mobility group transcription factor Sox8 as a physiologic regulator of bone formation. Sox8-deficient mice display a low bone mass phenotype that is caused by a precocious osteoblast differentiation. Accordingly, primary osteoblasts derived from these mice show an accelerated mineralization ex vivo and a premature expression of osteoblast differentiation markers. To confirm the function of Sox8 as a negative regulator of osteoblast differentiation we generated transgenic mice that express Sox8 under the control of an osteoblast-specific Col1a1 promoter fragment. These mice display a severely impaired bone formation that can be explained by a strongly reduced expression of runt-related transcription factor 2, a gene encoding a transcription factor required for osteoblast differentiation. Together, these data demonstrate a novel function of Sox8, whose tightly controlled expression is critical for bone formation.

Show MeSH

Related in: MedlinePlus

Decreased Runx2 expression in Col1a1-Sox8 transgenic mice. (A) Von Kossa staining of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice after 0, 10, and 20 d of incubation with ascorbic acid and β-glycerophosphate. Mineralization of the transgenic cultures is delayed and reduced compared with wild-type cultures. (B) RT-PCR expression analysis of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice at d0, d10, and d20 of differentiation. Note the decreased expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic cultures. (C) A Northern blot expression analysis using calvaria and femur RNA from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old reveals a reduced expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic bones. (D) An electrophoretic mobility shift assay using the Runx2-binding site (OSE-2) reveals the presence of Runx2 in nuclear extracts from differentiating wild-type cells (d5 and d10), but not in cells derived from transgenic mice. This binding was not observed with a mutated binding site (mutOSE-2) or in the presence of an anti–Runx2-antibody. (E) Analysis of tibia sections from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old. Von Kossa staining shows the osteoporotic phenotype in the primary spongiosa of transgenic mice (top). Immunohistochemistry using an antibody against Runx2 reveals that the expression of Runx2 is down-regulated in Col1a1-Sox8 transgenic mice (middle). The counter-staining with DAPI is shown below. (F) Schematic presentation explaining the phenotypes of both mouse models and illustrating the deduced role of Sox8 as a negative regulator of osteoblast differentiation. In osteoblast precursor cells the presence of Sox8 limits the amount of Runx2 expression keeping the cells in a proliferative state. In differentiated osteoblasts Sox8 is not expressed, and Runx2 can activate the osteogenic cascade leading to bone formation.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2171778&req=5

fig8: Decreased Runx2 expression in Col1a1-Sox8 transgenic mice. (A) Von Kossa staining of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice after 0, 10, and 20 d of incubation with ascorbic acid and β-glycerophosphate. Mineralization of the transgenic cultures is delayed and reduced compared with wild-type cultures. (B) RT-PCR expression analysis of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice at d0, d10, and d20 of differentiation. Note the decreased expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic cultures. (C) A Northern blot expression analysis using calvaria and femur RNA from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old reveals a reduced expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic bones. (D) An electrophoretic mobility shift assay using the Runx2-binding site (OSE-2) reveals the presence of Runx2 in nuclear extracts from differentiating wild-type cells (d5 and d10), but not in cells derived from transgenic mice. This binding was not observed with a mutated binding site (mutOSE-2) or in the presence of an anti–Runx2-antibody. (E) Analysis of tibia sections from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old. Von Kossa staining shows the osteoporotic phenotype in the primary spongiosa of transgenic mice (top). Immunohistochemistry using an antibody against Runx2 reveals that the expression of Runx2 is down-regulated in Col1a1-Sox8 transgenic mice (middle). The counter-staining with DAPI is shown below. (F) Schematic presentation explaining the phenotypes of both mouse models and illustrating the deduced role of Sox8 as a negative regulator of osteoblast differentiation. In osteoblast precursor cells the presence of Sox8 limits the amount of Runx2 expression keeping the cells in a proliferative state. In differentiated osteoblasts Sox8 is not expressed, and Runx2 can activate the osteogenic cascade leading to bone formation.

Mentions: To confirm that the phenotype of the Col1a1-Sox8 transgenic mice is caused by an intrinsic osteoblast differentiation defect we analyzed the behavior of primary calvarial osteoblasts from transgenic mice and wild-type littermates. In contrast to wild-type cultures, no mineralized bone nodules were observed after 10 d of differentiation in transgenic cultures. After 20 d only few areas were mineralized in transgenic cultures, whereas wild-type cultures displayed many mineralized nodules (Fig. 8 A). We next performed an RT-PCR expression analysis for osteoblast differentiation markers. In contrast to the Sox8-deficient cultures, we observed a delayed and reduced expression of Osc, Bsp, Phex, Runx2, and Col1a1 compared with wild-type cultures, whereas Lrp5 expression was not significantly changed (Fig. 8 B). Again, these results were confirmed in vivo by Northern blot expression analysis using RNA from calvaria and femur of Col1a1-Sox8 transgenic mice and wild-type littermates at 2 wk old (Fig. 8 C).


The high mobility group transcription factor Sox8 is a negative regulator of osteoblast differentiation.

Schmidt K, Schinke T, Haberland M, Priemel M, Schilling AF, Mueldner C, Rueger JM, Sock E, Wegner M, Amling M - J. Cell Biol. (2005)

Decreased Runx2 expression in Col1a1-Sox8 transgenic mice. (A) Von Kossa staining of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice after 0, 10, and 20 d of incubation with ascorbic acid and β-glycerophosphate. Mineralization of the transgenic cultures is delayed and reduced compared with wild-type cultures. (B) RT-PCR expression analysis of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice at d0, d10, and d20 of differentiation. Note the decreased expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic cultures. (C) A Northern blot expression analysis using calvaria and femur RNA from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old reveals a reduced expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic bones. (D) An electrophoretic mobility shift assay using the Runx2-binding site (OSE-2) reveals the presence of Runx2 in nuclear extracts from differentiating wild-type cells (d5 and d10), but not in cells derived from transgenic mice. This binding was not observed with a mutated binding site (mutOSE-2) or in the presence of an anti–Runx2-antibody. (E) Analysis of tibia sections from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old. Von Kossa staining shows the osteoporotic phenotype in the primary spongiosa of transgenic mice (top). Immunohistochemistry using an antibody against Runx2 reveals that the expression of Runx2 is down-regulated in Col1a1-Sox8 transgenic mice (middle). The counter-staining with DAPI is shown below. (F) Schematic presentation explaining the phenotypes of both mouse models and illustrating the deduced role of Sox8 as a negative regulator of osteoblast differentiation. In osteoblast precursor cells the presence of Sox8 limits the amount of Runx2 expression keeping the cells in a proliferative state. In differentiated osteoblasts Sox8 is not expressed, and Runx2 can activate the osteogenic cascade leading to bone formation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171778&req=5

fig8: Decreased Runx2 expression in Col1a1-Sox8 transgenic mice. (A) Von Kossa staining of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice after 0, 10, and 20 d of incubation with ascorbic acid and β-glycerophosphate. Mineralization of the transgenic cultures is delayed and reduced compared with wild-type cultures. (B) RT-PCR expression analysis of primary osteoblast cultures from wild-type and Col1a1-Sox8 transgenic mice at d0, d10, and d20 of differentiation. Note the decreased expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic cultures. (C) A Northern blot expression analysis using calvaria and femur RNA from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old reveals a reduced expression of Col1a1, Osc, Bsp, Phex, and Runx2 in transgenic bones. (D) An electrophoretic mobility shift assay using the Runx2-binding site (OSE-2) reveals the presence of Runx2 in nuclear extracts from differentiating wild-type cells (d5 and d10), but not in cells derived from transgenic mice. This binding was not observed with a mutated binding site (mutOSE-2) or in the presence of an anti–Runx2-antibody. (E) Analysis of tibia sections from wild-type and Col1a1-Sox8 transgenic mice at 2 wk old. Von Kossa staining shows the osteoporotic phenotype in the primary spongiosa of transgenic mice (top). Immunohistochemistry using an antibody against Runx2 reveals that the expression of Runx2 is down-regulated in Col1a1-Sox8 transgenic mice (middle). The counter-staining with DAPI is shown below. (F) Schematic presentation explaining the phenotypes of both mouse models and illustrating the deduced role of Sox8 as a negative regulator of osteoblast differentiation. In osteoblast precursor cells the presence of Sox8 limits the amount of Runx2 expression keeping the cells in a proliferative state. In differentiated osteoblasts Sox8 is not expressed, and Runx2 can activate the osteogenic cascade leading to bone formation.
Mentions: To confirm that the phenotype of the Col1a1-Sox8 transgenic mice is caused by an intrinsic osteoblast differentiation defect we analyzed the behavior of primary calvarial osteoblasts from transgenic mice and wild-type littermates. In contrast to wild-type cultures, no mineralized bone nodules were observed after 10 d of differentiation in transgenic cultures. After 20 d only few areas were mineralized in transgenic cultures, whereas wild-type cultures displayed many mineralized nodules (Fig. 8 A). We next performed an RT-PCR expression analysis for osteoblast differentiation markers. In contrast to the Sox8-deficient cultures, we observed a delayed and reduced expression of Osc, Bsp, Phex, Runx2, and Col1a1 compared with wild-type cultures, whereas Lrp5 expression was not significantly changed (Fig. 8 B). Again, these results were confirmed in vivo by Northern blot expression analysis using RNA from calvaria and femur of Col1a1-Sox8 transgenic mice and wild-type littermates at 2 wk old (Fig. 8 C).

Bottom Line: This is achieved through a balanced activity of bone-resorbing osteoclasts and bone-forming osteoblasts.In this study, we identify the high mobility group transcription factor Sox8 as a physiologic regulator of bone formation.Together, these data demonstrate a novel function of Sox8, whose tightly controlled expression is critical for bone formation.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biochemistry, Friedrich-Alexander-University, Erlangen-Nürnberg, Erlangen 91054, Germany.

ABSTRACT
Bone remodeling is an important physiologic process that is required to maintain a constant bone mass. This is achieved through a balanced activity of bone-resorbing osteoclasts and bone-forming osteoblasts. In this study, we identify the high mobility group transcription factor Sox8 as a physiologic regulator of bone formation. Sox8-deficient mice display a low bone mass phenotype that is caused by a precocious osteoblast differentiation. Accordingly, primary osteoblasts derived from these mice show an accelerated mineralization ex vivo and a premature expression of osteoblast differentiation markers. To confirm the function of Sox8 as a negative regulator of osteoblast differentiation we generated transgenic mice that express Sox8 under the control of an osteoblast-specific Col1a1 promoter fragment. These mice display a severely impaired bone formation that can be explained by a strongly reduced expression of runt-related transcription factor 2, a gene encoding a transcription factor required for osteoblast differentiation. Together, these data demonstrate a novel function of Sox8, whose tightly controlled expression is critical for bone formation.

Show MeSH
Related in: MedlinePlus