The primary objective of this study was to develop molecular tools to distinguish the cellular subtypes or stages of the oligodendrocyte lineage. Immunohistochemistry and functional studies including lineage tracing and cell and protein turnover studies were performed in mice to establish BCAS1+ cells as an oligodendroglial subpopulation. The formation of BCAS1+ oligodendrocytes during remyelination was determined in two experimental models of demyelination and lysolecithin- and cuprizone-induced demyelination. Immunohistochemical studies were performed to associate BCAS1+ cells with developmental myelination along the life span of a human brain. The brain tissue of patients with MS was examined to establish BCAS1+ cells as a cellular marker of ongoing remyelination in the disease. The number of biological replicates (n) per experiment is noted in each figure legend. The quantitative analyses were performed blinded. No outlier removal was performed.