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L Pedraza

Publications and source records attributed to L Pedraza.

18 recordsLinked to original sources
PubMed2001

Organizing principles of the axoglial apparatus.

On axonal surfaces that flank the node of Ranvier and in overlying glial paranodal loops, proteins are arranged within circumscribed microdomains that defy explanation by conventional biosynthetic mechanisms. We postulate that the constraint of proteins to these loci is accomplished in part by discriminative membrane-embedded molecular sieves and diffusion barriers, which serve to organize and redistribute proteins after delivery by vesicular transport to neural cell plasma membranes. One sieve likely comprises a moveable, macromolecular scaffold of axonal and glial cell-derived transmembrane adhesion molecules and their associated cytoplasmic binding partners, located at the ends of each elongating myelin internode; this sieve contributes to restricting the sodium channel complexes to the node. We also anticipate the existence of a passive paranodal diffusion barrier at the myelin/noncompact membrane border, which prohibits protein diffusion out of contiguous paranodal membranes.

Animals↗
PubMed2000

An oligodendrocyte cell adhesion molecule at the site of assembly of the paranodal axo-glial junction.

Two major isoforms of the cell adhesion molecule neurofascin NF186 and NF155 are expressed in the central nervous system (CNS). We have investigated their roles in the assembly of the node of Ranvier and show that they are targeted to distinct domains at the node. At the onset of myelination, NF186 is restricted to neurons, whereas NF155 localizes to oligodendrocytes, the myelin-forming glia of the CNS. Coincident with axon ensheathment, NF155 clusters at the paranodal regions of the myelin sheath where it localizes in apposition to the axonal adhesion molecule paranodin/contactin-associated protein (Caspr1), which is a constituent of the septate junction-like axo-glial adhesion zone. Immunoelectron microscopy confirmed that neurofascin is a glial component of the paranodal axo-glial junction. Concentration of NF155 with Caspr1 at the paranodal junctions of peripheral nerves is also a feature of Schwann cells. In Shiverer mutant mice, which assemble neither compact CNS myelin nor normal paranodes, NF155 (though largely retained at the cell body) is also distributed at ectopic sites along axons, where it colocalizes with Caspr1. Hence, NF155 is the first glial cell adhesion molecule to be identified in the paranodal axo-glial junction, where it likely interacts with axonal proteins in close association with Caspr1.

Animals↗
PubMed2000

Fluorescent myelin proteins provide new tools to study the myelination process.

We present here a new approach which permits us to follow myelin proteins within living, actively myelinating cells. We have developed probes to study the spatial and temporal incorporation of proteins into the myelin sheath by expressing myelin proteins fused to the green fluorescent protein (GFP). GFP from the jellyfish Aequorea victoria and its derivatives, e.g., blue fluorescent protein (BFP) were used as molecular reporters to monitor the intracellular distribution of myelin proteins. Fusion proteins (14 kD myelin basic protein [MBP]-GFP, 21 kD MBP-GFP) were expressed in primary Schwann cells (SCs) and their distribution was monitored by confocal microscopy. The autofluorescent chimeric proteins were readily visualized and their subcellular localization was unaffected by the GFP reporter. However, because of the length of culturing time necessary to establish permanent cell lines, we found that it was not possible to obtain MBP-GFP stable SCs that also were capable of myelinating neuronal axons. We therefore devised a way of introducing vectors under conditions where cells are dividing in response to endogenous stimuli, and therefore are still capable of myelinating. We designed a protocol in which SCs cocultured with dorsal root ganglion (DRG) neurons are transfected while they are actively dividing. SCs transfected in this way exhibit a good level of protein expression and retain their myelinating phenotype. The fusion protein expression lasts long enough to observe "green myelin. " These fluorescently tagged myelin proteins will allow high-resolution examination of the protein and membrane traffic in normal myelinating cells.

Axons↗
PubMed1998

Asking residents about adverse events in a computer dialogue: how accurate are they?

BACKGROUND: Although retrospective identification of adverse events is time-consuming, whether they are present and/or expected is often readily apparent to providers during the provision of care. METHODS: A computer program to flag admissions with possible adverse events was developed. Readmissions to the hospital within 31 days and admissions including more than one visit to the operating room (OR) were flagged. For surgical site infections, all admissions--including a visit to the OR--were flagged, but only a sample was evaluated in the reliability assessment. Residents in an urban, tertiary care hospital were questioned when inputting computerized discharge orders regarding adverse events among 391 cases sampled from 6,813 admissions for a two-month period. RESULTS: For the 228 readmissions (3.3% of all admissions) identified by the computer program, resident responses had a sensitivity of 57% and a specificity of 73% in detecting an unexpected readmission (nurse responses, 96% and 91%). For the 79 patients with a return to the OR, the residents' responses had a sensitivity of 86% and a specificity of 84% for detecting an unexpected return (versus 75% and 98% for the nurses' responses). For the 209 patients with an OR visit, the sensitivity and specificity for a surgical site infection were 85% and 98% for the residents and 54% and 99% for the nurses. DISCUSSION: Information systems can be used to screen for adverse events and to ask providers whether adverse events are unexpected, although the reliability of this approach is likely to vary by event type.

Boston↗
PubMed1997

Nuclear transport of myelin basic protein.

The multiple myelin basic protein (MBP) isoforms expressed by myelinating cells are now known to have different expression patterns. The relative abundance of the isoforms containing exon II is greater early in myelinogenesis, whereas in compact myelin the isoforms lacking this exon are more abundant. Further, the individual MBPs exhibit different intracellular localizations, indicating that the isoforms may not be functionally equivalent in myelinating cells. The major MBPs (14 kD and 18.5 kD) have strong affinity for membranes, while on the other hand, the less abundant isoforms (17 kD and 21.5 kD) localize to the nucleus of young oligodendrocytes, suggesting a regulatory role in the myelination program. The same intracellular distribution patterns have been observed when the MBPs are expressed in Hela cells and in shiverer oligodendrocytes. Thus, the intracellular fate of these proteins seems to be generally directed through alternative expression of exon II. Furthermore, the extent of MBPexII entry into the nucleus was found to be directly related to the growth state of host cells. In this paper, we demonstrate that nuclear proteins constitutively expressed by Hela cells also exhibit an apparently growth-related nucleo-cytoplasmic distribution revealing that MBPexII exhibits the same behavior as bona fide nuclear proteins. Also, to further characterize MBP nuclear transport, we explored various parameters of the translocation of MBP into the nucleus using an in vitro system. This experimental paradigm permits the uncoupling of synthesis and translocation events; thus, the transport of MBP into cell nuclei can be studied as a function of time. We also evaluated how changes in temperature as well as energy depletion affect the in vitro nuclear transport of MBP.

Biological Transport↗
PubMed1997

The active transport of myelin basic protein into the nucleus suggests a regulatory role in myelination.

The myelin basic proteins (MBPs) are a set of membrane proteins that function to adhere the cytoplasmic leaflets of the myelin bilayer. During oligodendrocyte maturation prior to compact myelin formation, however, certain MBPs have been observed within the cell body and nucleus. We explored the parameters of the translocation of the exon II-containing MBPs (MBPexII) from the site of synthesis in the cell cytoplasm into the nucleus and in some experiments used GFP as a molecular reporter to monitor the intracellular distribution of MBP-GFP fusion proteins in living cells. We show here that the transport of MBPexII into cell nuclei is an active process, which is temperature and energy dependent, and may be regulated by phosphorylation state. Further, MBPexII can direct the entry of macromolecular complexes into cell nuclei, revealing that the exon II peptide segment may provide a nuclear localization signal (NLS), perhaps a novel one, or may induce a conformational change in the full-length protein that exposes a cryptic NLS. The MBPexII are thus very unusual in that they are plasma membrane proteins that are also targeted to the nucleus. In oligodendrocytes and Schwann cells, where the MBPs are naturally expressed, it is likely that karyophilic MBPs subserve a regulatory function in implementing the myelination program.

Biological Transport, Active↗
PubMed1996

Membrane adhesion and other functions for the myelin basic proteins.

The myelin basic proteins are a set of peripheral membrane polypeptides which play an essential role in myelination. Their most well-documented property is the unique ability to 'seal' the cytoplasmic aspects of the myelin membrane, but this is probably not the only function for these highly charged molecules. Despite extensive homology, the individual myelin basic proteins (MBPs) exhibit different expression patterns and biochemical properties, and so it is now believed that the various isoforms are not functionally equivalent in myelinating cells. We now think that while the major MBPs are intracellular adhesion molecules, some of the quantitatively less abundant isoforms that are expressed very early in development may have regulatory effects on the myelination program.

Animals↗
PubMed1996

[Chronic inflammatory demyelinating polyneuropathy. Report of six cases].

Chronic inflammatory demyelinating polyneuropathy is a heterogeneous disease characterized by symmetrical motor and sensitive alterations, absence of tendon reflexes and increased cerebrospinal fluid protein levels. We report 6 patients with the disease, (three males) aged 41 to 70 years old. Four had the classical presentation and two had an asymmetrical paresis, that predominated in superior limbs. These patients had a proximal block with scarce prolongation of distal nerve conduction velocity. In all patients, underlying illnesses were discarded with a full diagnostic work up. Subjects were followed from 2 to 14 months after the diagnosis. In all, treatment with steroids improved muscle strength and sensitivity.

Adult↗
PubMed1995

Biosynthesis and regulation of expression of the HNK-1 epitope on myelin-associated glycoprotein in a transfected cell model system.

The HNK-1 antibody recognizes a carbohydrate epitope expressed by many cell adhesion molecules in the nervous system that has been proposed to be an important adhesive determinant. This epitope is particularly prominent on the myelin-associated glycoprotein (MAG) and is related to the antigenic target in an autoimmune mediated demyelinating neuropathy. Elucidation of the mechanisms underlying the biosynthesis and regulation of expression of the HNK-1 epitope is therefore likely to have important functional and clinical implications. In order to investigate its biosynthesis and the regulation of its expression, we have expressed both human and rat MAG in several different cell lines by retroviral infection. These studies indicate that the cellular milieu determines whether the HNK-1 epitope is expressed on the MAG polypeptide and provide an explanation for the significant variation in HNK-1 levels that has been noted in different species. Using a transfected human neuroblastoma line, we have determined that this epitope is present on the fourth and/or fifth immunoglobulin-like domain of rat MAG and that it is added intracellularly, probably in the trans Golgi. Finally we have found that expression of the HNK-1 epitope is increased by activation of different second messenger systems, providing direct evidence that its expression can be regulated independently from that of the MAG polypeptide.

Animals↗
PubMed1991

Differential expression of MAG isoforms during development.

The myelin-associated glycoproteins (MAG) mediate the cell interactions of oligodendrocytes and Schwann cells with axons that are myelinated. MAG exists in two developmentally regulated isoforms: large MAG (L-MAG) and small MAG (S-MAG). In this paper, we have studied the tissue-specific and developmentally regulated alternative splicing of these isoforms using monospecific antibodies that recognize epitopes common to both isoforms or that are present only on L-MAG. In the central nervous system (CNS), L-MAG is the major form synthesized early in development, and it persists as a significant proportion of the MAG present in the adult. In the peripheral nervous system (PNS), L-MAG is expressed at modest levels during development; it is virtually absent in the adult. Thus, the expression of L-MAG is not limited to the CNS, as was formerly believed, suggesting that it plays a common role during the early stages of myelin formation by both oligodendrocytes and Schwann cells. In both the CNS and PNS, S-MAG is the predominant isoform in the adult. A higher-molecular-weight form of MAG is present in the PNS at low abundance, that is developmentally regulated, and appears to be a glycosylation variant. An analysis of the carbohydrate residues on MAG demonstrates that it contains both N-linked and O-linked sugars that could be modulated during development. These results suggest a possible mechanism for the regulation of MAG function during myelinogenesis via the expression of alternative isoforms and carbohydrate modifications.

Animals↗
PubMed1991

Joubert syndrome. Respiratory failure requiring home mechanical ventilation.

A case of Joubert's Syndrome with respiratory insufficiency requiring mechanical ventilatory support is presented. The case illustrates the complex clinical, ethical and technical aspects in the management of patients with this syndrome and the feasibility of extending mechanical ventilatory support to the home setting. A caring, knowledgeable care team and a loving supportive family are required to properly continue treatment in the home in cases of this rare syndrome.

Abnormalities, Multiple↗
PubMed1991

[Sneddon syndrome. Presentation of 2 cases].

Sneddon syndrome is a systemic non inflammatory arteriopathy characterized by the association of livedo reticularis, thrombotic cerebrovascular disease, coronary artery disease and hypertension. Middle age females are usually affected. It should be considered in the differential diagnosis of acute ischemic attacks in younger patients. It has been related to the antiphospholipid antibody syndrome. Treatment is based on control of hypertension and cardiovascular risk factors along with antiplatelet agents. Two cases meeting the clinical criteria outlined above are reported.

Adult↗
PubMed1990

The myelin-associated glycoproteins: membrane disposition, evidence of a novel disulfide linkage between immunoglobulin-like domains, and posttranslational palmitylation.

The myelin-associated glycoproteins (MAG) are members of the immunoglobulin gene superfamily that function in the cell interactions of myelinating glial cells with axons. In this paper, we have characterized the structural features of these proteins. The disposition of MAG in the bilayer as a type 1 integral membrane protein (with an extracellularly disposed amino terminus, single transmembrane segment, and cytoplasmic carboxy terminus) was demonstrated in protease protection studies of MAG cotranslationally inserted into microsomes in vitro and in immunofluorescent studies with site specific antibodies. A genetically engineered MAG cDNA, which lacks the putative membrane spanning segment, was constructed and shown to encode a secreted protein. These results confirm the identify of this hydrophobic sequence as the transmembrane segment. Sequencing of the secreted protein demonstrated the presence of a cleaved signal sequence and the site of signal peptidase cleavage. To characterize the disulfide linkage pattern of the ectodomain, we cleaved MAG with cyanogen bromide and used a panel of antibodies to coprecipitate specific fragments under nonreducing conditions. These studies provide support for a novel disulfide linkage between two of the immunoglobulin domains of the extracellular segment. Finally, we report that MAG is posttranslationally palmitylated via an intramembranous thioester linkage. Based on these studies, we propose a model for the conformation of MAG, including its RGD sequence, which is considered with regard to its function as a cell adhesion molecule.

Animals↗