The 2010 McDonald criteria for the diagnosis of multiple sclerosis are widely used in research and clinical practice. Scientific advances in the past 7 years suggest that they might no longer provide the most up-to-date guidance for clinicians and researchers. The International Panel on Diagnosis of Multiple Sclerosis reviewed the 2010 McDonald criteria and recommended revisions. The 2017 McDonald criteria continue to apply primarily to patients experiencing a typical clinically isolated syndrome, define what is needed to fulfil dissemination in time and space of lesions in the CNS, and stress the need for no better explanation for the presentation. The following changes were made: in patients with a typical clinically isolated syndrome and clinical or MRI demonstration of dissemination in space, the presence of CSF-specific oligoclonal bands allows a diagnosis of multiple sclerosis; symptomatic lesions can be used to demonstrate dissemination in space or time in patients with supratentorial, infratentorial, or spinal cord syndrome; and cortical lesions can be used to demonstrate dissemination in space. Research to further refine the criteria should focus on optic nerve involvement, validation in diverse populations, and incorporation of advanced imaging, neurophysiological, and body fluid markers.

The vertebrate nervous system is characterized by ensheathment of axons with myelin, a multilamellar membrane greatly enriched in the galactolipid galactocerebroside (GalC) and its sulfated derivative sulfatide. We have generated mice lacking the enzyme UDP-galactose:ceramide galactosyltransferase (CGT), which is required for GalC synthesis. CGT-deficient mice do not synthesize GalC or sulfatide but surprisingly form myelin containing glucocerebroside, a lipid not previously identified in myelin. Microscopic and morphometric analyses revealed myelin of normal ultrastructural appearance, except for slightly thinner sheaths in the ventral region of the spinal cord. Nevertheless, these mice exhibit severe generalized tremoring and mild ataxia, and electrophysiological analysis showed conduction deficits consistent with reduced insulative capacity of the myelin sheath. Moreover, with age, CGT-deficient mice develop progressive hindlimb paralysis and extensive vacuolation of the ventral region of the spinal cord. These results indicate that GalC and sulfatide play important roles in myelin function and stability.

The vertebrate myelin sheath is greatly enriched in the galactolipids galactocerebroside (GalC) and sulfatide. Mice with a disruption in the gene that encodes the biosynthetic enzyme UDP-galactose:ceramide galactosyl transferase (CGT) are incapable of synthesizing these lipids yet form myelin sheaths that exhibit major and minor dense lines with spacing comparable to controls. These CGT mutant mice exhibit a severe tremor that is accompanied by hindlimb paralysis. Furthermore, electrophysiological studies reveal nerve conduction deficits in the spinal cord of these mutants. Here, using electron microscopic techniques, we demonstrate ultrastructural myelin abnormalities in the CNS that are consistent with the electrophysiological deficits. These abnormalities include altered nodal lengths, an abundance of heminodes, an absence of transverse bands, and the presence of reversed lateral loops. In contrast to the CNS, no ultrastructural abnormalities and only modest electrophysiological deficits were observed in the peripheral nervous system. Taken together, the data presented here indicate that GalC and sulfatide are essential in proper CNS node and paranode formation and that these lipids are important in ensuring proper axo-oligodendrocyte interactions.

To address the effect of host proteins on the self-splicing properties of the group I introns of bacteriophage T4, we have purified an activity from EscherJchia coil extracts that facilitates both trans-and c/s-splicing of the T4 introns in vitro. The activity is attributable to a number of proteins, several of which are ribosomal proteins. Although these proteins have variable abilities to stimulate splicing, ribosomal protein S12 is the most effective. The activity mitigates the negative effects on splicing of the large internal open reading frames (ORFs) common to the T4 introns. In contrast to proteins shown previously to facilitate group I splicing, S12 does not bind strongly or specifically to the intron. Rather, S12 binds RNA with broad specificity and can also facilitate the action of a hammerhead ribozyme. Addition of S12 to unreactive trans-splicing precursors promoted splicing, suggesting that S12 can resolve misfolded RNAs. Furthermore, incubation with $12 followed by its proteolytic removal prior to the initiation of the splicing reaction still resulted in splicing enhancement. These results suggest that this protein facilitates splicing by acting as an RNA chaperone, promoting the assembly of the catalytically active tertiary structure of ribozymes. [ Bacteriophage T4 contains three self-splicing group I in-trons located in the structural genes for thymidylate syn-thase (td), ribonucleotide reductase (nrdB), and a putative anaerobic ribonucleotide reductase (sunY} (Chu et al. 1984; Gott et al. 1986; Shub et al. 1987; Sun et al. 1993). These introns splice by the typical group I pathway, via two transesterification reactions initiated by nucleo-philic attack of guanosine at the 5' splice site. This process depends on conserved secondary and tertiary structures that direct folding of the intron such that the 5' and 3' splice sites are juxtaposed to the guanosine-binding site within the intron's catalytic core (Cech 1990; Michel and Westhof 1990; Cech et al. 1992; Saldanha et al. 1993). Although a number of group I introns (including the T4 introns} self-splice in vitro, evidence points to involvement of accessory factors during in vivo splicing. 4present address: Brain and

Glycosphingolipids and cholesterol form lateral assemblies, or lipid ÔraftsÕ, within biological membranes. Lipid rafts are routinely studied biochemically as low-density, detergentinsoluble complexes (in non-ionic detergents at 4°C; DIGs, detergent-insoluble glycosphingolipid/cholesterol microdomains). Recent discrepancies recommended a re-evaluation of the conditions used for the biochemical analysis of lipid rafts. We have investigated the detergent insolubility of several known proteins present in the glycosphingolipid/ cholesterol-rich myelin membrane, using four detergents representing different chemical classes (TX-100, CHAPS, Brij 96 and TX-102), under four conditions: detergent extraction of myelin either at (i) 4°C or (ii) 37°C, or at 4°C after pre-extraction with (iii) saponin or (iv) methyl-b-cyclodextrin (MbCD). Each detergent was different in its ability to solubilize myelin proteins and in the density of the DIGs produced. Brij 96 DIGs floated to a lower density than other detergents tested, possibly representing a subpopulation of DIGs in myelin. DIGs pre-extracted with saponin were denser than DIGs pre-extracted with MbCD. Furthermore, pre-extraction with MbCD solubilized proteolipid protein (known to associate with cholesterol), whereas pre-extraction with saponin did not, suggesting that saponin is less effective as a cholesterol-perturbing agent than is MbCD. These results demonstrate that DIGs isolated by different detergents are not necessarily comparable, and that these detergent-specific DIGs may represent distinct biochemical, and possibly physiological, entities based on the solubilities of specific lipids/proteins in each type of detergent.

Myelin is a dynamic, functionally active membrane necessary for rapid action potential conduction, axon survival, and cytoarchitecture. The number of debilitating neurological disorders that occur when myelin is disrupted emphasizes its importance. Using highresolution 2D gel electrophoresis, mass spectrometry, and immunoblotting, we have developed an extensive proteomic map of proteins present in myelin, identifying 98 proteins corresponding to at least 130 of the Ϸ200 spots on the map. This proteomic map has been applied to analyses of the localization and function of selected proteins, providing a powerful tool to investigate the diverse functions of myelin.M yelin is a dynamic, functionally active membrane (1), the loss or damage of which results in serious neurological disorders including leukodystrophies, central and peripheral neuropathies, and inflammatory demyelinating diseases such as multiple sclerosis (2-4). Rapid and efficient action potential conduction in the nervous system depends on myelin, which traditionally has been viewed as a passive contributor to conduction by increasing internodal membrane resistance and decreasing membrane capacitance (5). However, recent work has revealed additional active roles for myelin in nervous system development and function. For example, myelin regulates axon diameter and the formation of axon microtubular networks, and it is a key player in ion channel clustering at nodes of Ranvier (6-11). In return, the axon regulates myelin gene expression (12) and oligodendrocyte survival (13). The functional coupling of myelin and axons is further illustrated by the transfer of phospholipids (14) and N-acetylaspartate (15) from the axon to the myelin sheath.A major impediment to understanding the active biological functions of myelin is the relative lack of myelin proteins that have been described and characterized. Thus, we have undertaken an extensive proteomic analysis of central nervous system myelin, developed a 2D PAGE map of myelin proteins, identified 98 of these proteins, and illustrated the power and utility of this approach through specific applications of comparative proteomics. For example, a comparison of CNS and peripheral nervous system (PNS) myelin proteins has revealed a previously undescribed component of Schwann cell microvilli, a proteomic matching of myelin from normal and genetically modified mice lacking key myelin lipids has demonstrated a dramatic reduction of two newly recognized myelin protein kinases, and an application of the map to a neuroimmunological analysis of demyelinating disease has identified a signaling mechanism (16).

Myelin oligodendrocyte glycoprotein (MOG) is, quantitatively, a relatively minor component of the myelin membrane. Nevertheless, peritoneal administration of MOG evokes potent cellular and humoral immunoreactivity, resulting in an experimental allergic encephalitis with immunopathology similar to multiple sclerosis. Moreover, antibodies against MOG cause myelin destruction in situ. Therefore, it appears that MOG-related demyelination is dependent on anti-MOG antibody, but the mechanism(s) by which it occurs is unclear. Of potential significance are observations that some proteins are selectively partitioned into specialized plasma membrane microdomains rich in glycosphingolipids and cholesterol ("lipid rafts"). In particular, during ligand or antibody cross-linking, various plasma membrane receptors undergo enhanced partitioning into rafts as an obligatory first step toward participation in early signal transduction events. In contrast to mature myelin, in oligodendrocytes (OLs) in culture MOG is not raft associated [Triton X-100 (TX-100) soluble, 4 degrees C]. However, in this study we show that antibody cross-linking (anti-MOG plus secondary antibody) of MOG on the surface of OLs results in the repartitioning of approximately 95% of MOG into the TX-100-insoluble fraction. This repartitioning of MOG is rapid (

Despite significant progress in the development of therapies for relapsing MS, progressive MS remains comparatively disappointing. Our objective, in this paper, is to review the current challenges in developing therapies for progressive MS and identify key priority areas for research. A collaborative was convened by volunteer and staff leaders from several MS societies with the mission to expedite the development of effective disease-modifying and symptom management therapies for progressive forms of multiple sclerosis. Through a series of scientific and strategic planning meetings, the collaborative identified and developed new perspectives on five key priority areas for research: experimental models, identification and validation of targets and repurposing opportunities, proof-of-concept clinical trial strategies, clinical outcome measures, and symptom management and rehabilitation. Our conclusions, tackling the impediments in developing therapies for progressive MS will require an integrated, multi-disciplinary approach to enable effective translation of research into therapies for progressive MS. Engagement of the MS research community through an international effort is needed to address and fund these research priorities with the ultimate goal of expediting the development of disease-modifying and symptom-relief treatments for progressive MS.