SOX9 Governs Differentiation Stage-Specific Gene Expression in Growth Plate Chondrocytes via Direct Concomitant Transactivation and Repression

Abstract

Cartilage and endochondral bone development require SOX9 activity to regulate chondrogenesis, chondrocyte proliferation, and transition to a non-mitotic hypertrophic state. The restricted and reciprocal expression of the collagen X gene, Col10a1, in hypertrophic chondrocytes and Sox9 in immature chondrocytes epitomise the precise spatiotemporal control of gene expression as chondrocytes progress through phases of differentiation, but how this is achieved is not clear. Here, we have identified a regulatory element upstream of Col10a1 that enhances its expression in hypertrophic chondrocytes in vivo. In immature chondrocytes, where Col10a1 is not expressed, SOX9 interacts with a conserved sequence within this element that is analogous to that within the intronic enhancer of the collagen II gene Col2a1, the known transactivation target of SOX9. By analysing a series of Col10a1 reporter genes in transgenic mice, we show that the SOX9 binding consensus in this element is required to repress expression of the transgene in non-hypertrophic chondrocytes. Forced ectopic Sox9 expression in hypertrophic chondrocytes in vitro and in mice resulted in down-regulation of Col10a1. Mutation of a binding consensus motif for GLI transcription factors, which are the effectors of Indian hedgehog signaling, close to the SOX9 site in the Col10a1 regulatory element, also derepressed transgene expression in non-hypertrophic chondrocytes. GLI2 and GLI3 bound to the Col10a1 regulatory element but not to the enhancer of Col2a1. In addition to Col10a1, paired SOX9–GLI binding motifs are present in the conserved non-coding regions of several genes that are preferentially expressed in hypertrophic chondrocytes and the occurrence of pairing is unlikely to be by chance. We propose a regulatory paradigm whereby direct concomitant positive and negative transcriptional control by SOX9 ensures differentiation phase-specific gene expression in chondrocytes. Discrimination between these opposing modes of transcriptional control by SOX9 may be mediated by cooperation with different partners such as GLI factors.

Transcription Factor SOX9 Promotes Osteosarcoma Cell Growth by Repressing Claudin-8 Expression [Retraction]

“…SOX9 plays a key role in the regulation of sex determination, intestinal differentiation, cartilage development and adult progenitor cell pool maintenance (Jakob and LovellBadge 2011). During endochondral bone formation, SOX9 expression is down-regulated in growth plate chondrocytes (Leung et al 2011). The exact role of SOX9 in carcinogenesis and cancer progression is controversial because both oncogenic and tumor-suppressing functions of SOX9 have been described (Passeron et al 2009;Cai et al 2013;.…”

Artificial cartilage bio-matrix formed of hyaluronic acid and Mg2+-polyphosphate

“…This high cell compatibility of the HA-Mg 2+ -Na-polyP matrix was also reflected by the degree of gene inducibility elicited by this paste in comparison the free HA or Na-polyP. The qRT-PCR studies revealed that the gene encoding the transcription factor SOX9, which regulates chondrocyte differentiation, proliferation and entry into hypertrophy in immature and proliferating chondrocytes (Leung et al, 2011), was only significantly upregulated after a 21 d incubation period in chondrocytes in comparison to the controls (without any component), to HA or to Na-polyP alone. Likewise, the paste strongly enhanced the expression of collagen 3A1 (COL3A1), a cartilage matrix protein, marker for differentiation of chondrocytes both in vivo and in vitro (Aigner et al, 1997).…”

Hedgehog-Gli Activators Direct Osteo-chondrogenic Function of Bone Morphogenetic Protein toward Osteogenesis in the Perichondrium

“…Given that Sox9 is required for the expressions of Sox5 and Sox6 (3) and Sox9 transcription is suggested to be controlled by Sox9 itself (39), the initial events in this context may be an inhibition of the recruitment of Sox9 into its own regulatory regions by Gli1. However, a recent paper showed that there were conserved Gli-binding sites near the Sox motif in the Sox5 and Sox6 regions (40), which raised the possibility that an inhibitory action by Gli1 might occur in these regions. This study, however, does not address how Gli1 inhibits the recruitment of Sox9 onto DNA.…”