Sunday, January 25, 2009

Osterix


Differential gene expression by Osterix knockdown in mouse chondrogenic ATDC5 cells.

ATDC5 cells are more look chondrocyte progenitor cells than stem cells.
"Osterix (Osx) is a transcription factor required for osteoblast differentiation during intramembranous and endochondral ossification. In an vitro study, which the effects of Osx gene silencing were examined in mouse chondrogenic ATDC5 cells, chondrocyte marker genes were found to be expressionally downregulated and chondrocyte differentiation to be reduced. On the other hand, in vivo studies based on chondrocyte-specific Osx knockouts demonstrated impaired endochondral bone formation with delayed chondrocyte differentiation and reduced cartilage matrix ossification. We investigate global gene expression profile changes caused by Osx knockdown in ATDC5 chondrocytes. The mRNA expressions of 112 genes were significantly modified by Osx knockdown: 68 genes were upregulated and 44 genes downregulated. Functional categories of gene expression classified by gene ontology demonstrated that genes related to cell adhesion, development, and signal transduction were highly affected by Osx knockdown. The expressions of differential genes, such as Sfrp2, Sema3a, Nox4, Rgs4, Zfp521, Has2, Sox6, Scn2a1, Sirpa, and Thbs2, were validated by quantitative real-time PCR."

"Osx gene silencing in mouse chondrogenic ATDC5 cells caused the downregulated expression of chondrocyte marker genes and reduced chondrocyte differentiation"

"Rgs5, Rgs7, and Rgs10 promote chondrocyte differentiation, Rgs4 has an inhibitory effect."

"In chondrocytes, Zfp521 acts on a downstream target gene of PTHR1 signaling and regulates cellular proliferation and differentiation"

"chondrocyte-specific Has2 inactivation causes skeletal deformities and abnormal organization within chondrocytes"

Genes upregulated in Osx knockdown ATDC5 cells also up in LSJL:
Thbs2
Serinc2
Cadm1{down}
Pcsk2{down}
Plscr2{down}
Ppp1r3c
Embigin{down as A430106F12Rik}
Aspn
Htra1
Fgd4{down}

Downregulated:
Anxa8{up}
Sdpr
Gpr115{up}
Creb3l1{up}
Cdh18{up}
Rcbtb2
Rbm26

Haploinsufficiency of Osterix in Chondrocytes Impairs Skeletal Growth in Mice.

"Osteoblast-specific ablation of Osx using Col1α1-Cre resulted in osteopenia, due to impaired osteoblast differentiation in adult mice. Osx is expressed in chondrocytes. We [examine] the skeletal phenotype of mice with conditional disruption of Osx in Col2α1 expressing chondrocytes. Surprisingly, Cre-positive mice that were homozygous for Osx floxed alleles died after birth. Alician blue and alizarin red staining revealed that the lengths of skeleton, femur and vertebrae were reduced by 21, 26 and 14%, respectively, in the knockout (KO) compared with wild type (WT) mice. In order to determine if haploid insufficiency of Osx in chondrocytes influenced postnatal skeletal growth, we compared skeletal phenotype of floxed heterozygous mice that were Cre-positive or Cre-negative. Body length was reduced by 8%, and areal BMD of total body, femur, and tibia was reduced by 5, 7, and 8% respectively in mice with conditional disruption of one allele of Osx in chondrocytes. Micro-CT showed reduced cortical vBMD and trabecular BV/TV in the femurs of Osxflox/+;col2α1-Cre mice. Histological analysis revealed that the impairment of longitudinal growth was associated with disrupted growth plates in the Osxflox/+;col2α1-Cre mice. Primary chondrocytes isolated from KO embryos showed reduced expression of chondral ossification markers, but elevated expression of chondrogenesis markers. Osx expressed in chondrocytes regulates bone growth in part by regulating chondrocyte hypertrophy."

Loss of Osterix downregulated Col10{up} and MMP13.  Loss of Osterix upregulated Fgfr3, Sox9{up}, TGFBr2, and HES1{up in LSJL}.

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