The broad aim of this project is to elucidate the transcription factors that control chondrocyte differentiation during vertebrate development. Prior work in my lab has established that Sonic Hedgehog (Shh) and Wnt signals pattern somitic cell fate. We have recently found that one of the genes induced by Shh, Nkx3.2, confers competence for subsequent BMP signals to induce chondrogenesis. Activation of somitic chondrogenesis by Nkx3.2 requires BMP signaling and correlates with the ability of this regulator to induce the expression of another chondrocyte transcription factor, Sox-9. We have found that the transcriptional repressor activity of Nkx3.2 requires interaction of Nkx3.2 with both BMP-dependent Smads and histone deacetylases and is necessary for Nkx3.2 to induce both somitic chondrogenesis and Sox-9 gene expression. Forced expression of Sox-9 in somites can similarly induce competence for subsequent BMP signals to induce chondrogenesis. Together, these findings suggest that Nkx3.2 induces a prochondrogenic state in somites by repressing the transcription of an inhibitor of Sox-9 expression. Later in development Nkx3.2 is specifically expressed in immature cartilage in the developing limb bud and is excluded from regions of chondrocyte hypertrophy. Forced expression of Nkx3.2 throughout the limb bud blocks chondrocyte maturation and chondrocyte hypertrophy. The transcriptional repressor activity of Nkx3.2 is necessary for this transcription factor to block cartilage maturation, and suggests that Nkx3.2 blocks the transcription of a factor(s) required for cartilage maturation. Our findings indicate that Nkx3.2 plays a role in the generation and maturation of cartilage cells. In this proposal I outline a series of experiments to address the following specific aims. (1) Determine how BMP-dependent SMADs promote chondrogenesis. (2) Determine if GATA genes repress a chondrogenic response to BMP signaling (3) Determine how Nkx3.2 represses chondrocyte maturation. (4) Determine if other Nkx family members expressed in the developing bones act together with Nkx3.2 to repress chondrocyte maturation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR048524-07
Application #
6892141
Study Section
Oral Biology and Medicine Subcommittee 1 (OBM)
Program Officer
Sharrock, William J
Project Start
1997-05-01
Project End
2008-04-30
Budget Start
2005-05-01
Budget End
2006-04-30
Support Year
7
Fiscal Year
2005
Total Cost
$318,660
Indirect Cost
Name
Harvard University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
047006379
City
Boston
State
MA
Country
United States
Zip Code
02115
Daoud, Georges; Kempf, Hervé; Kumar, Deepak et al. (2014) BMP-mediated induction of GATA4/5/6 blocks somitic responsiveness to SHH. Development 141:3978-87
Ionescu, Andreia; Kozhemyakina, Elena; Nicolae, Claudia et al. (2012) FoxA family members are crucial regulators of the hypertrophic chondrocyte differentiation program. Dev Cell 22:927-39
Kumar, Deepak; Lassar, Andrew B (2009) The transcriptional activity of Sox9 in chondrocytes is regulated by RhoA signaling and actin polymerization. Mol Cell Biol 29:4262-73
Kozhemyakina, Elena; Cohen, Todd; Yao, Tso-Pang et al. (2009) Parathyroid hormone-related peptide represses chondrocyte hypertrophy through a protein phosphatase 2A/histone deacetylase 4/MEF2 pathway. Mol Cell Biol 29:5751-62
Cairns, Dana M; Sato, Mie Elissa; Lee, Philip G et al. (2008) A gradient of Shh establishes mutually repressing somitic cell fates induced by Nkx3.2 and Pax3. Dev Biol 323:152-65
Kempf, Herve; Ionescu, Andreia; Udager, Aaron M et al. (2007) Prochondrogenic signals induce a competence for Runx2 to activate hypertrophic chondrocyte gene expression. Dev Dyn 236:1954-62
Provot, Sylvain; Kempf, Herve; Murtaugh, L Charles et al. (2006) Nkx3.2/Bapx1 acts as a negative regulator of chondrocyte maturation. Development 133:651-62
Kim, Dae-Won; Lassar, Andrew B (2003) Smad-dependent recruitment of a histone deacetylase/Sin3A complex modulates the bone morphogenetic protein-dependent transcriptional repressor activity of Nkx3.2. Mol Cell Biol 23:8704-17