PAK1 expression through the oligodendrocyte lineage. A, PAK1 protein expression in vitro in primary rOPCs. PAK1 has increased expression during oligodendrocyte differentiation, particularly when MBP is expressed. B, Quantification of in vitro expression of PAK1 protein (F(5,17) = 5.583, *p = 0.0032); ordinary one-way ANOVA with Dunnett's multiple comparisons test. C, Representative image of PAK1 expression in oligodendrocytes after 5 d in differentiation media. Green represents PAK1. Blue represents Olig2. Magenta represents O1/O4. Scale bar, 10 µm. D, E, In vivo expression of PAK1 by pEXPR-mbp:PAK1-EGFP coexpressed with pEXPR:mbp:mRFP to label myelin. In zebrafish larvae (4 dpf), PAK1 is expressed in the cell body, in presumptive paranodes (arrowheads), and within myelin (arrow). In P8 cortex, PAK1 protein is expressed in oligodendrocytes (E) (green represents PAK1; magenta represents SOX10), and P8 brains were fixed in methanol (see Materials and Methods). Scale bar, 25 µm.