Không giống như các tế bào dòng O-2A, loại 1 tế bào hình sao sinh sôi nảy nở trong phản ứng với yếu tố tăng trưởng biểu bì (EGF) (Raff et al, 1983a). Loại 1 tế bào hình sao phát triển sớm trong quá trình gliogenesis. GFAP / A2B5 tế bào hình sao đầu tiên xuất hiện trong huyền phù tế bào | Astrocyte Development Chapter 7 211 immunoreactivity with the antibody Ran-2 by their absence of immunoreactivity with the other antibodies listed above and by their separation from the oligodendrocyte lineage Raff et al. 1984 . Unlike the O-2A lineage cells type 1 astrocytes proliferate in response to epidermal growth factor EGF Raff et al. 1983a . Type 1 astrocytes develop early during gliogenesis. GF AP A2B5 astrocytes first appear in cell suspensions of developing rat optic nerve on embryonic day 16 E16 Miller et al. 1985 . Studies in forebrain cultures also support the early generation of astrocytes with a type 1 morphology and antigenic phenotype. For example they are clonally distinct from the other glial lineages by E16 in rat forebrain cultures Vaysse and Goldman 1992 . Culican et al. 1990 studied cultures from embryonic mouse forebrain and described cells with a radial glial-like morphology that bound the RC1 antibody a monoclonal antibody that labels radial glia in vivo Edwards et al. 1990 . While initially GFAP these cells became RC1 GFAP with time and eventually RC1 G1AP a developmental and antigenic sequence that suggests type 1 astrocytes are generated in vitro from radial glia. Applying the glial nomenclature derived from studies on optic nerve glia to other CNS regions can be problematic since morphology and antigen expression can vary. For instance studies of spinal cord astrocytes demonstrate that there is a greater variety of astrocyte types in the spinal cord than in optic nerve and furthermore that A2B5 cells from the spinal cord give rise to pancake -shaped spinal cord astrocytes that are distinct from type 1 astrocytes Miller and Szigeti 1991 Fok-Seang and Miller 1992 . While clonally related cells tended to be morphologically similar some are morphologically heterogeneous. Furthermore the expression of A2B5 and Ran-2 varies even among clonally related cells. These and other observations illustrate astrocyte heterogeneity in different CNS .
