Direct visualization of membrane architecture of myelinating cells in transgenic mice expressing membrane‐anchored EGFP

Abstract

Myelinogenesis is a complex process that involves substantial and dynamic changes in plasma membrane architecture and myelin interaction with axons. Highly ramified processes of oligodendrocytes in the central nervous system (CNS) make axonal contact and then extrapolate to wrap around axons and form multilayer compact myelin sheathes. Currently, the mechanisms governing myelin sheath assembly and axon selection by myelinating cells are not fully understood. Here, we generated a transgenic mouse line expressing the membrane-anchored green fluorescent protein (mEGFP) in myelinating cells, which allow live imaging of details of myelinogenesis and cellular behaviors in the nervous systems. mEGFP expression is driven by the promoter of 2′-3′-cyclic nucleotide 3′-phosphodiesterase (CNP) that is expressed in the myelinating cell lineage. Robust mEGFP signals appear in the membrane processes of oligodendrocytes in the CNS and Schwann cells in the peripheral nervous system (PNS), wherein mEGFP expression defines the inner layers of myelin sheaths and Schmidt-Lanterman incisures in adult sciatic nerves. In addition, mEGFP expression can be used to track the extent of remyelination after demyelinating injury in a toxin-induced demyelination animal model. Taken together, the membrane-anchored mEGFP expression in the new transgenic line would facilitate direct visualization of dynamic myelin membrane formation and assembly during development and process remodeling during remyelination after various demyelinating injuries.

Oligodendrocyte gene expression is reduced by and influences effects of chronic social stress in mice

“…It will be important to study gray matter and white matter subregions, as shown in mouse models for multiple sclerosis . Indeed, the availability of transgenic mice with labeled oligodendrocytes (for example see References ) will allow for analysis of stress effects on transcriptome and proteome in pure oligodendrocyte samples. Finally, it will be important to assess CSS effects on the myelin transcriptome …”

Uncovering the biology of myelin with optical imaging of the live brain

“…Cytoplasmic fluorescent proteins do not readily diffuse into compact myelin thus limiting analyses of internode structure using most conventional fluorescent protein labeling strategies. This can be overcome to some extent by using membrane targeted fluorescent proteins (Chong et al, ; Deng et al, ; Kirby et al, ; Young et al, ; Zhu et al, ). Another limitation of fluorescence labeling is the inability to determine when and where a labeled myelin segment is forming compact myelin.…”

“…As discussed below, the ability to image mouse cortex and spinal cord over strategies. This can be overcome to some extent by using membrane targeted fluorescent proteins Deng et al, 2014;Kirby et al, 2006;Young et al, 2013;Zhu et al, 2011). Another limitation of fluorescence labeling is the inability to determine when and where a labeled myelin segment is forming compact myelin.…”

Myelin plasticity, neural activity, and traumatic neural injury

“…For example, tritiated thymidine was used in a study that concluded oligodendrocytes proliferate in response to injury (Ludwin ), with the determination of oligodendrocytes based solely on cellular morphology. More recently, genetic or viral reporters of the oligodendrocyte lineage and membrane‐targeting reporters that visualize myelin have been developed (Powers et al, ; Deng et al, ; Hill et al, ). Though these reporters need not be restricted to injury, they have proved useful to isolate the source of newly generated oligodendrocytes and myelin following injury (e.g.…”

“…For example, tritiated thymidine was used in a study that concluded oligodendrocytes proliferate in response to injury (Ludwin 1984), with the determination of oligodendrocytes based solely on cellular morphology. More recently, genetic or viral reporters of the oligodendrocyte lineage and membranetargeting reporters that visualize myelin have been developed (Powers et al, 2013;Deng et al, 2014; Figure 1 Three models of myelin plasticity: (A) myelination of bare axons by new internodes: an OPC differentiates to form a new oligodendrocyte in order to myelinate an unmyelinated section of axon (B) remodeling or refinement of existing myelin: an existing sheath may lengthen, shorten, or thicken. In cross section, thickening of an internode reflects an increase in the number of myelin wraps (C) replacement of myelin sheaths by new internodes: two existing, short internodes retract from the axon, while an OPC leaves the cell cycle to differentiate and form a single longer sheath.…”