O2A progenitor cells transplanted into the neonatal rat brain develop into oligodendrocytes but not astrocytes.

Abstract

The differentiation of the bipotential 02Aprogenitor cell into an oligodendrocyte or a type 2 astrocyte has been well documented in cell cultures of various regions of the central nervous system. The appropriate tools to prove its existence in vivo have been lacking. We report on an in vitro-in vivo approach that combines stable labeling of an enriched population of cultured 02A progenitors by the fluorescent dye fast blue, followed by their transplantation into neonatal rat brains, which allowed us to study the influence of the brain microenvironment on their lineage decision. Recently, the existence of type 2 astrocytes in vivo has been questioned (6, 7). Raffand coworkers (5) have estimated the in vivo appearance of type 1 astrocytes, oligodendrocytes, and type 2 astrocytes in the rat optic nerve to be at postnatal day 0 (PO), P4, and P15, respectively. However, a light and electron microscopic immunocytochemical analysis of [3H]thymidine pulse-labeled developing rats has revealed only two periods of astrocyte and oligodendrocyte generations, the earliest being that of GFAP+ cells near PO followed by a wave of oligodendrocytes at P4-P8 (6, 7). A major obstacle to resolve this controversy has been the lack of appropriate markers to identify type 2 astrocytes in the brain (5). The antibody A2B5 is not a reliable marker in tissue sections because it stains unrelated cell types and intracellular structures (for review, see refs. 7 and 8).In this study, we propose an approach to compare the fate of 02A progenitors in the in vivo vs. in vitro environment. An enriched population of 02A progenitors in culture was labeled with the fluorescent dye fast blue (FB) and transplanted into neonatal rat brains. The phenotypic differentiation of 02A cells was studied in tissue sections by single and double immunolabeling and examined by fluorescence microscopy to visualize grafted cells and their progeny. We have reported (9) that FB-labeled cultured glial cells transplanted into normal and myelin-deficient (md) Wistar rats remain identifiable in immunostained tissue sections up to 6 months after grafting (9). We now report that transplanted 02A progenitors in vivo develop into oligodendrocytes but not astrocytes. MATERIALS AND METHODSAnimals. Normal Wistar and md Wistar rat pups were raised in our breeding colonies. Rats were housed in a restricted-access temperature-controlled vivarium on a 12-h light/12-h dark cycle, with free access to food and water. Fifty percent of pups born to previously identified female carriers of the md trait are genetically normal (+/y) and 50% carry the md trait (md/y). Males ofboth genotypes were used at P5 as recipients for cell transplants.Cell Culture. Primary cultures were prepared from newborn rat brains as described (10). These cultures were maintained in Waymouth medium supplemented with 10% (vol/ vol) fetal calf serum. After 9 days in culture, 02A cells growing on top ofthe astrocyte monolayer (type 1 astrocytes) were removed by a modification of the method of McCarthy and de Vel...

Glucocorticoids and progestins signal the initiation and enhance the rate of myelin formation

“…Cultured oligodendrocytes are capable of forming myelin-like sheets independent of neurons, although the interactions with neurons are still essential in producing proper myelin internodes. O-2A cells appear to generate myelinating oligodendrocytes but not type 2 astrocytes when cocultured in the presence of neurons (49). Thus, the induction of the enzymes involved in steroid biosynthesis in oligodendrocytes independent of neurons does not exclude the possibility that interactions between the two cells will change the pattern of expression.…”

NG2 cells generate both oligodendrocytes and gray matter astrocytes

“…Transplanted OPCs have not been shown to generate astrocytes in the host CNS (Groves et al, 1993;Espinosa de los Monteros et al, 1993) except under pathological astrocyte-free conditions (Franklin et al, 1995). Based on these observations, the astrocytic fate of OPCs [O-2A progenitor cells (Raff et al, 1983)] has been generally discarded as an in vitro artifact.…”

“…It is well established that in culture, OPCs can give rise to both oligodendrocytes and type-2 astrocytes (Raff et al, 1983). The search for an astrocytic fate of NG2 glia in vivo has not yielded positive results because of the lack of evidence for the existence of cells that co-express NG2 and astrocytic markers and the lack of evidence that transplanted OPCs generate astrocytes in the CNS (Reynolds et al, 2002;Nishiyama et al, 2002;Nishiyama et al, 2005;Groves et al, 1993;Espinosa de los Monteros et al, 1993). Other studies, however, suggest that there may be glial progenitor cells that can give rise to both oligodendrocytes and astrocytes.…”

A Common Progenitor for Retinal Astrocytes and Oligodendrocytes

“…Studies of cultures derived from dissociated rat optic nerve suggested that glial progenitor cells, the O2A cells, give rise to both type 2 astrocytes and oligodendrocytes (Raff et al, 1983a(Raff et al, , 1984Temple and Raff, 1985). However, two groups transplanted labeled O2A cells into the developing brain and found that only oligodendrocytes were produced, suggesting that there are distinct progenitors for astrocytes and oligodendrocytes (Espinosa de los Monteros et al, 1993;Groves et al, 1993). Subsequent studies in various systems led to the proposal that there are distinct domains for astrocyte and oligodendrocyte production, supporting the notion of distinct progenitors for the two glial types (Rowitch, 2004).…”