Functions as a negative regulator of MYRF in oligodendrocyte differentiation and myelination. Interacts with the C-terminal of MYRF inhibiting MYRF self-cleavage and N-fragment nuclear translocation. The secreted form promotes differentiation of T helper 1 cells (Th1). Interacts (via N-terminal region) with MYRF; the interaction inhibits MYRF self-cleavage. Secreted by exosomes through a non-classical pathway. Widely expressed with high expression in the ovary, pancreas and prostate (PubMed:25946230). Expressed in the eye, particularly in corneal endothelium, iris, ciliary body, sclera, optic nerve, optic nerve head, and retina (PubMed:24852644). Expressed by activated peripheral blood mononuclear cells (PubMed:25946230). The disease is caused by variants affecting the gene represented in this entry. Belongs to the TMEM98 family.