Endochondral ossification is a process by which mesenchymal progenitor cells (MPCs) differentiate into cartilage prior to forming bone. Perturbations in their capacity to differentiate leads to skeletal anomalies. Therefore, deciphering the molecular mechanisms controlling these cells is crucial for both understanding the causes of skeletal diseases as well as developing new therapeutic approaches to restore the skeleton. While transcription factors and signaling molecules have been linked to cartilage development, less is known about the upstream mechanisms that initiate the process. Recent data from mice and humans implicate epigenetic regulatory factors as critical modulators of MPC function. CXXC finger protein 1 (Cfp1) is an epigenetic regulatory factor implicated in progenitor cell function, though the mechanism(s) of its action have not been well defined. To address this, we deleted Cfp1 specifically from limb bud mesenchyme. Preliminary data show that loss of Cfp1 results in the complete absence of forelimbs at birth. Subsequent analysis of embryonic forelimbs revealed that, in the absence of Cfp1, MPCs failed to undergo condensation, the initial step in chondrogenesis. Whole transcriptome analysis revealed a dramatic reduction in chondrogenic gene markers, including the master transcriptional regulator, Sox9, which is required for condensation, further implicating Cfp1 as a crucial factor in the early stages of cartilage formation. Preliminary data indicate that Cfp1 may regulate this key developmental step through activation of BMP signaling. Further, while mutant hindlimbs form they are severely stunted, consistent with our observation that deletion of Cfp1 in chondrocytes results in shorter bones. Together, these data suggest that Cfp1 also regulates chondrocyte differentiation and maturation during growth plate development. We hypothesize that Cfp1 regulates multiple stages of cartilage development through modulation of essential transcriptional regulators and key signaling pathways. Further study of Cfp1 will provide fundamental insight into how epigenetic regulation of cellular and molecular mechanisms impacts chondrogenesis and growth plate development. We propose: 1) to identify Cfp1's actions during chondrocyte differentiation in the developing long bone, 2) to determine the effect of Cfp1 loss on growth plate development and 3) to identify the Cfp1 regulatory network during cartilage development.
Transcription factors and signaling molecules are key modulators of cartilage development, with alterations in either resulting in skeletal anomalies. We have identified a factor that is required for cartilage formation, presumably through its ability to regulate the expression of components of both of these groups. Results from this study will determine whether and how this factor controls transcription factors and signaling molecules during cartilage development, which may impact our therapeutic approach to correct skeletal defects.
