, 2002) were bred with an Olig1-Cre line, in which

Cre recombinase is produced in the oligodendrocyte lineage ( Xin et al., 2005 and Ye et al., 2009) ( Figure 2A). We observed that all resulting mutant Sip1flox/flox;Olig1Cre+/− mice (referred to as Sip1cKO), but not their control littermates, developed generalized tremors, hindlimb paralysis, and seizures from postnatal week 2 ( Figure 2B, upper panel), although they were born at a normal Mendelian ratio. Sip1cKO mice exhibited the phenotypes reminiscent of myelin-deficient mice ( Nave, 1994) and died around postnatal week 3, in contrast to the normal lifespan of wild-type (WT) and Sip1 conditional heterozygous FK228 clinical trial control (Sip1flox/+;Olig1Cre+/−) mice ( Figure 2C). The optic nerve, a well-characterized CNS white matter tract, from Sip1cKO mice was translucent compared to the control ( Figure 2B, lower panels), which is a sign of severe deficiency in myelin formation. To confirm the myelin-deficient phenotypes, we examined myelin gene expression in

Sip1cKO mice. In contrast to robust expression in control mice, expression of myelin genes such as Mbp (myelin basic protein) and Plp1 (proteolipid protein) is essentially undetectable in the forebrain, spinal cord, and cerebellum of mutant mice at P14 (Figures 2D and 2F). In light of our data demonstrating that expression of mature oligodendrocyte markers was absent in Sip1cKO mice, we further examined myelin sheath assembly in the CNS of these mutants by electron microscopy. In contrast to a large number of myelinated axons Z-VAD-FMK order that are observed in control mice at P14 (Figures 2G and 2H, upper panels), they were completely absent in the optic nerve

and spinal cord of Sip1cKO mutants (Figures 2G and 2H, lower panels), indicating that myelin ensheathment has not begun in these animals. These results suggest that Sip1 is required for myelinogenesis in the CNS. Despite the deficiency in myelin gene expression, the OPC marker PDGFRα was detected in the brain these and the spinal cord in the mutant mice (Figures 3A and 3B). The number of OPCs and their proliferation rate (percentage of Ki67+ proliferating OPCs) in Sip1 mutants were comparable to control mice ( Figures 3C and 3D). We did not detect any significant cell death in the brain and spinal cord of Sip1cKO mice at P7 and P14 based on TUNEL assay and staining for the active form of caspase-3 (n = 3; data not shown). In addition, oligodendrocyte lineage-specific Sip1 inactivation did not lead to obvious alterations of astrocytes and neurons marked by GFAP and NeuN, respectively, in the brain of Sip1cKO mice ( Figure S2). Our data indicate that OPCs are able to form in the CNS of Sip1cKO mice. To investigate whether the differentiation capacity of OPCs in the absence of Sip1 in vitro is blocked, we carried out Cre-mediated Sip1 excision in cultures of purified OPCs.