Transcription factor that plays a key role in several developmental processes, including neurogenesis, chondrocytes differentiation and cartilage formation (Probable). Specifically binds the 5'-AACAAT-3' DNA motif present in enhancers and super-enhancers and promotes expression of genes important for chondrogenesis (PubMed:9755172, PubMed:11702786). Required for overt chondrogenesis when condensed prechondrocytes differentiate into early stage chondrocytes: SOX5 and SOX6 cooperatively bind with SOX9 on active enhancers and super-enhancers associated with cartilage-specific genes, and thereby potentiate SOX9's ability to transactivate (PubMed:11702786, PubMed:15529345, PubMed:26150426). Not involved in precartilaginous condensation, the first step in chondrogenesis, during which skeletal progenitors differentiate into prechondrocytes (PubMed:14993235, PubMed:26150426). Together with SOX5, required to form and maintain a pool of highly proliferating chondroblasts between epiphyses and metaphyses, to form columnar chondroblasts, delay chondrocyte prehypertrophy but promote hypertrophy, and to delay terminal differentiation of chondrocytes on contact with ossification fronts (PubMed:14993235). Binds to the proximal promoter region of the myelin protein MPZ gene, and is thereby involved in the differentiation of oligodendroglia in the developing spinal tube (PubMed:26525805). Binds to the gene promoter of MBP and acts as a transcriptional repressor (PubMed:26525805). Homodimer (PubMed:32442410). Interacts with DAZAP2 (PubMed:14530442). May interact with CENPK (PubMed:10996314). Additional isoforms seem to exist. Highly expressed in testis. Expression is transiently increased during brown adipocyte differentiation. Expression is dependent on SOX9. Sumoylation inhibits the transcriptional activity. Newborn mice display mild skeletal abnormalities (PubMed:11702786). Knockout mice also display increase in prematurely differentiated oligodendrocyte precursor cells in the motor neuron progenitor domain of the spinal tube at 11.5 dpc (PubMed:26525805). At 18.5 dpc the number and distribution of oligodendroglia are normal, however there is an increased number of differentiating oligodendrocytes (PubMed:26525805). Double knockout of Sox13 and Sox6 show an increase in oligodendrocyte precursor cells in the spinal tube at 11.5 dpc, at 18.5 dpc the number and distribution of oligodendroglia are normal but contain an increased number of differentiating cells (PubMed:26525805). Mice lacking both Sox5 and Sox6 develop a severe chondrodysplasia characterized by the virtual absence of cartilage: chondrogenic cells are largely arrested at the stage of chondrogenic mesenchymal condensations (PubMed:11702786). Embryos lacking Sox5 (homozygous knockout) and heterozygous for Sox6 live until birth and show severe growth plate chondrocyte defects (PubMed:14993235). Embryos lacking Sox6 (homozygous knockout) and heterozygous for Sox5 live until birth and show severe growth plate chondrocyte defects (PubMed:14993235).