Rumpshaker-like proteolipid protein (PLP) ratio in a mouse model with unperturbed structural and functional integrity of the myelin sheath and axons in the central nervous system

The gene plp on the X chromosome encodes the isoforms proteolipid protein ( PLP) and DM20, two dominant integral membrane proteins of central nervous s ystem (CNS) myelin. DM20, results from the activation of the cryptic splice site in exon III of the PLP gene. We inserted a sense-orientated loxP flan ked neomycin-gene into intron III of the plp sequence, using homologous rec ombination in embryonic stem cells and generated the homozygous neoS mouse line. Unlike the previously described complete PLP/DM20 ablation (plp(-/-)) , which has been obtained by introducing a neo-gene in antisense-orientatio n in the same position of intron III, the plp expression surprisingly revea led reduced mRNA levels. The PLP isoform was reduced to 50%, but DM20 expre ssion was unaffected. This protein pattern resembles the expression profile of the PLP isoforms in the natural occurring rumpshaker mutant. Electron m icroscopic examination revealed a normal compaction of CNS-myelin and maint enance of axon integrity. PLP expression levels of the wt control were reco vered by Cre excision of the neo-selection gene after intercrossing neoS mi ce and oligodendrocyte-specific Cre-mice. These data strongly hint at diffe rent functions of intron III in PLP/DM20-specific splicing and mRNA stabili ty. Furthermore evidence is provided for functionally affected translation products of the PLP gene in the rumpshaker mutant, whereas no PLP-isoform o ccur in plp(-/-) mice generated by introducing a selectable marker into int ron III in antisense orientation. GLIA 35:63-71, 2001. (C) 2001 Wiley-Liss, Inc.