ABSTRACT
We have studied the developmental appearance of the O-2Aadult progenitor cell, a specific type of oligodendro cyte-type-2 astrocyte (O-2A) progenitor cell that we have identified previously in cultures prepared from the optic nerves of adult rats. O-2Aadult progenitors differ from their counterparts in perinatal animals (O-2Aperina,al progenitor cells) in antigenic phenotype, morphology, cell cycle time, rate of migration, time course of differen tiation into oligodendrocytes or type-2 astrocytes and sensitivity to the lytic effects of complement in vitro. In the present study, we have found that O-2Aadult progeni tor-like cells first appear in the developing optic nerve approximately 7 days after birth and that by 1 month after birth these cells appear to be the dominant progeni tor population in the nerve. Howevér, the perinatal-to-adult transition in progenitor populations is a gradual one and O-2Aadult and O-2Aptrinata progenitors coexist in the optic nerve for 3 weeks or more. In addition, cells derived from optic nerves of P21 rats express character istic features of O-2Aadultand O-2Aptrinata progenitors for extended periods of growth in the same tissue culture dish. Our results thus indicate that the properties that distinguish these two types of O-2A progenitors from each other are expressed in apparently identical environ ments. Thus, these cells must either respond to different signals present in the environment, or must respond with markedly different behaviours to the binding of identical signalling molecules.