Transcription factor that binds to DNA at the consensus sequence 5'-ACCAAAG-3' (PubMed:18505825, PubMed:18403418, PubMed:30190287). Acts as a transcriptional activator (PubMed:18505825, PubMed:18403418, PubMed:30190287). Binds cooperatively with POU3F2/BRN2 or POU3F1/OCT6 to gene promoters, which enhances transcriptional activation (PubMed:18505825, PubMed:18403418). Involved in the differentiation of naive CD4-positive T-cells into peripherally induced regulatory T (pT reg) cells under inflammatory conditions (PubMed:30190287). Binds to the promoter region of the FOXP3 gene and promotes its transcription, and might thereby contribute to pT reg cell differentiation in the spleen and lymph nodes during inflammation (PubMed:30190287). Plays a redundant role with SOX4 and SOX11 in cell survival of developing tissues such as the neural tube, branchial arches and somites, thereby contributing to organogenesis (PubMed:20596238). Expressed in splenic and thymic regulatory T-cells (at protein level) (PubMed:30190287). Expressed in embryonic molar and incisor teeth (PubMed:8921394). Widely expressed in the developing embryo from 9.5 dpc to 12.5 dpc (PubMed:8441686, PubMed:18505825, PubMed:18403418, PubMed:20596238). Expressed throughout the central and peripheral nervous system, as well as the mesenchyme of many developing organs between 12.5 dpc and 14.5 dpc (PubMed:18403418). Strongly expressed in the lens of the eye, developing cerebral cortex, the dorsal cortical plate, thalamus, hippocampus and cerebellar cortex in the brain at 14.5 dpc (PubMed:18505825). Expressed in skin, spinal cord, lung, liver, intestine, kidney, heart, muscle, cartilage from 14.5 dpc to 18.5 dpc (PubMed:18505825). Abundantly expressed in the brain, heart and lung, with low expression in the liver, pancreas, and small intestine at postnatal day 2 (PubMed:18403418). Induced by T-cell receptor signaling in naive CD4-positive T-cells and in splenic and thymic regulatory T-cells (PubMed:30190287). Up-regulated in splenic T reg cells by dextran sulfate sodium (DSS)-induced colitis (PubMed:30190287). Knockout mice are viable, fertile and morphologically normal (PubMed:18505825, PubMed:20596238). Increased expression of Sox11 in brain and cartilage at 14.5 dpc, with increased expression in liver and kidney at 16.5 dpc (PubMed:18505825). Increased expression of Sox4 in spinal cord and cartilage at 14.5 dpc, with increased expression in liver at 16.5 dpc (PubMed:18505825). Sox12 knockout naive CD4-positive T cells fail to differentiate into pT reg cells in mice with dextran sulfate sodium (DSS)-induced colitis (PubMed:30190287). Sox4, Sox11, and Sox12 triple knockout mice are embryonically lethal and show severe thinning and undulation of the neural tube (PubMed:20596238).