Fig. 5. Cell commitment and differentiation in colonies from foetal EPCs. Twenty-five percent of GFP+ cells isolated from foetal NLBs expressed Sox10 (A1,A2) but were negative for MASH1 (B1,B2) or RET (C1,C2). On day 3, Sox10 expression was detected only in colony-associated cells (D1,D2), suggesting strongly that only the GFP+/SOX10+ EPCs have clonogenic potential. At this stage, only a subset of cells expressed Mash1 (E1,E2) or Ret (F1,F2) but we detected no TuJ1+ cells (G1,G2). On day 10, Sox10 was expressed in a subset of cells in the colonies (H2,I2). At this stage, all colonies contained PGP9.5+ cells (H1) which were negative for SOX10 (H3; arrow points to a PGP9.5+/SOX10-cell and arrowhead points to a neighbouring PGP9.5-/SOX10+ cell). Also, at this stage 87% of the colonies contained GFAP+ cells (I1) which maintained expression of Sox10 (I3; arrows point to GFAP+/SOX10+ cells). Cells expressing high levels of PGP9.5 were negative for MASH1 (J1-J3). Also, GFAP and MASH1 are present on mutually exclusive cells (K1-K3). Finally, the highest levels of RET were detected in TuJ1+ cells (L1-L3; arrows in L3) but GFAP+ cells did not express Ret (M1-M3).