Temporal and spatial profiles of ABCA2-expressing oligodendrocytes in the developing rat brain

ABCA2 protein belongs to the ABCA subclass of ATP-binding cassette (ABC) transporters proposed to exert critical functions in transmembrane transport of endogenous lipids. In this study, we found by immunoblot analyses that approximately 260 kDa of ABCA2 protein is expressed predominantly in oligodendrocytes, and that the expression of the protein is upregulated in the brain during maturation, especially between postnatal days 6 and 19. Parallel to the changes in expression of ABCA2, immunohistochemical analyses showed rapid spatial spread of ABCA2-immunolabeled oligodendrocytes in the brain during this period. These temporal and spatial changes in ABCA2 expression were in good agreement with findings in myeloarchitectonics reported previously. Further, double immunolabeling with ABCA2 and a major structural protein of myelin, myelin basic protein, demonstrated that onset of ABCA2 expression in oligodendrocytes coincides with the appearance of thick myelin segments immunolabeled with myelin basic protein. Because ABCA2 was abundantly expressed in adult cortex in white matter and gray matter, coexpression of ABCA2 and a marker for the oligodendroglial progenitors NG2 or platelet-derived growth factor alpha receptor was investigated. No cells coexpressing ABCA2 and the marker were observed, suggesting that ABCA2 is expressed predominantly in myelin-forming oligodendrocytes distinct from the adult oligodendroglial progenitors tested. These results suggested a role for ABCA2 in membrane transport of substrates such as the lipids that are closely linked to myelination processes.