Expression of a catalytically inactive transmembrane protein tyrosine phosphatase epsilon (tm-PTP epsilon) delays optic nerve myelination.
Reversible tyrosine phosphorylation is integral to the process of oligodendrocyte differentiation. To interfere with the subset of the phosphorylation cycle overseen by protein tyrosine phosphatase epsilon (PTP epsilon) in oligodendrocytes, we applied a substrate-trapping approach in the development of transgenic mice overexpressing a catalytically inactive, transmembrane PTP epsilon-hemaglutinin (tm-PTP epsilon-HA) from the dual promoter element of the gene encoding the myelin protein 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). Transgene expression peaked during the active myelinating period, at 2-3 weeks postnatal. Two tyrosine phosphoproteins, alpha-enolase and beta-actin, were phosphorylated to a greater degree in transgenic mice. Despite a high degree of tm-PTP epsilon-HA expression, myelin was grossly normal in nearly all axonal tracts. Phenotypic abnormalities were limited to optic nerve, where a decrease in the degree of myelination was reflected by reduced levels of myelin proteins on postnatal day 21 (PND21), as well as a decrease in the density of differentiated oligodendrocytes. The optic chiasm was reduced in thickness in transgenic mice; optic nerves similarly exhibited a reduction in transverse width. Further analyses of the optic pathway demonstrated that transgenic protein was unexpectedly present in retinal ganglion cells, whose axons are the targets of myelination by optic nerve oligodendrocytes. On PND28, transgenic protein declined dramatically in both oligodendrocytes and retinal ganglion cells contributing to the recovery of optic nerve myelination. Thus, delayed myelination arises only when tm-PTP epsilon-HA is simultaneously expressed in myelin-forming glia and their neuronal targets. While tm-PTP epsilon related signaling pathways may figure in axon-glial interactions, interfering with tm-PTP epsilon activity does not perceptibly affect the development or myelinating capacity of most oligodendrocytes.
Muja
Naser
N
Section of Developmental Genetics, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4160, USA.
Lovas
Gabor
G
Romm
Elena
E
Machleder
Dietrich
D
Ranjan
Mukul
M
Gallo
Vittorio
V
Hudson
Lynn D
LD
D000818:Animals; D020134:Catalytic Domain / Q000235:genetics; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008809:Mice, Inbred C3H; D008822:Mice, Transgenic; D009413:Nerve Fibers, Myelinated / Q000201:enzymology*; D009836:Oligodendroglia / Q000201:enzymology / Q000378:metabolism; D009900:Optic Nerve / Q000201:enzymology*; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4
D008565:Membrane Proteins; D017027:Protein Tyrosine Phosphatases; C098067:Ptpre protein, mouse; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4