The Role of the SOX11 Transcription Factor in Regulating Growth Differentiation Factor‐5 During Joint Formation

Abstract

Growth differentiation factor 5 (GDF5) is associated with the formation and maintenance of joints. Disruption of GDF5 expression is also linked to accelerated osteoarthritis. We have identified a GDF5 Associated Regulatory Region (GARR) that contains several Sox binding sites. The SOX11 transcription factor has been shown to upregulate GDF5 and we hypothesized that SOX11 is necessary for GARR mediated expression of GDF5 during joint development and maintenance. To test this hypothesis, we compared the expression of SOX11 and GDF5 in chicken limbs during development using in-situ hybridization, using MYOD, TNMD, and Col1A2 as muscle and tendon markers. We also generated a GARR reporter construct and mutated the Sox binding sites. The native and mutated GARR reporters were transfected into developing chick wings. Our results showed that in chicken, SOX11 expression primarily surrounds GDF5 expression in joint spaces at Hamburger-Hamilton stages (HH) 25-27. At HH 29, the expression of SOX11 and GDF5 colocalized in joint spaces. SOX11 expression was not confined to joints, but also found in muscles (MYOD) and tendons (TNMD, Col1A2). Disruption of the Sox binding sites greatly reduced GARR activity within joint spaces. Colocalization of SOX11 and GDF5 in joints shows that SOX11 may play a role in the regulation of GDF5 through GARR. Additionally, it may be a competency factor for the formation and organization of joint-related tissues. Decreased activity with mutant GARR suggests it is required for GARR activity. Further experiments are needed to clarify the role of SOX11 in regulating joints and joint associated tissues.