Peripheral Nerve Myelin Research Articles

Atomic resolution view into the structure-function relationships of the human myelin peripheral membrane protein P2.

P2 is a fatty acid-binding protein expressed in vertebrate peripheral nerve myelin, where it may function in bilayer stacking and lipid transport. P2 binds to phospholipid membranes through its positively charged surface and a hydrophobic tip, and accommodates fatty acids inside its barrel structure. The structure of human P2 refined at the ultrahigh resolution of 0.93 Å allows detailed structural analyses, including the full organization of an internal hydrogen-bonding network. The orientation of the bound fatty-acid carboxyl group is linked to the protonation states of two coordinating arginine residues. An anion-binding site in the portal region is suggested to be relevant for membrane interactions and conformational changes. When bound to membrane multilayers, P2 has a preferred orientation and is stabilized, and the repeat distance indicates a single layer of P2 between membranes. Simulations show the formation of a double bilayer in the presence of P2, and in cultured cells wild-type P2 induces membrane-domain formation. Here, the most accurate structural and functional view to date on P2, a major component of peripheral nerve myelin, is presented, showing how it can interact with two membranes simultaneously while going through conformational changes at its portal region enabling ligand transfer.

New Mutation in Periaxin Gene Causing Charcot Marie Tooth Disease in a Puerto Rican Young Male

Charcot-Marie-Tooth (CMT) disease is an inherited peripheral neuropathy caused by mutations in more than 30 different genes. One of the genes encodes for periaxin (PRX) protein, which is required for the maintenance of peripheral nerve myelin. Individuals with PRX gene mutations have been described to present early-onset, autosomal recessive, demyelinating CMT disease or CMT4F subtype. Only 23 mutations involving the PRX gene have been reported in patients throughout the world. We describe a case of a Puerto Rican adolescent with history, neurologic examination, electromyographic data, and laboratory tests consistent with CMT4F. Genetic analysis of this individual showed a heterozygous transversion resulting in amino acid change from arginine to glycine in the PRX gene, suggesting CMT4F. We report this novel PRX mutation to expand the clinical spectrum of CMT disease.

Collagen VI regulates peripheral nerve myelination and function

Collagen VI is an extracellular matrix protein with broad distribution in several tissues. Although Col6a1 is expressed by Schwann cells, the role of collagen VI in the peripheral nervous system (PNS) is yet unknown. Here we show that Schwann cells, but not axons, contribute to collagen VI deposition in peripheral nerves. By using Col6a1-null mice, in which collagen VI deposition is compromised, we demonstrate that lack of collagen VI leads to increased myelin thickness (P<0.001) along with 60-130% up-regulation in myelin-associated proteins and disorganized C fibers in the PNS. The hypermyelination of PNS in Col6a1(-/-) mice is supported by alterations of signaling pathways involved in myelination, including increase of P-FAK, P-AKT, P-ERK1, P-ERK2, and P-p38 (4.15, 1.67, 2.47, 3.34, and 2.60-fold, respectively) and reduction of vimentin (0.49-fold), P-JNK (0.74-fold), and P-c-Jun (0.50-fold). Pathologically, Col6a1(-/-) mice display an impairment of nerve conduction velocity and motor coordination (P<0.05), as well as a delayed response to acute pain stimuli (P<0.001), indicating that lack of collagen VI causes functional defects of peripheral nerves. Altogether, these results indicate that collagen VI is a critical component of PNS contributing to the structural integrity and proper function of peripheral nerves.

Liposomes to Target Peripheral Neurons and Schwann Cells

While a wealth of literature for tissue-specific liposomes is emerging, optimal formulations to target the cells of the peripheral nervous system (PNS) are lacking. In this study, we asked whether a novel formulation of phospholipid-based liposomes could be optimized for preferential uptake by microvascular endothelia, peripheral neurons and Schwann cells. Here, we report a unique formulation consisting of a phospholipid, a polymer surfactant and cholesterol that result in enhanced uptake by targeted cells. Using fluorescently labeled liposomes, we followed particle internalization and trafficking through a distinct route from dextran and escape from degradative compartments, such as lysosomes. In cultures of non-myelinating Schwann cells, liposomes associate with the lipid raft marker Cholera toxin, and their internalization is inhibited by disruption of lipid rafts or actin polymerization. In contrast, pharmacological inhibition of clathrin-mediated endocytosis does not significantly impact liposome entry. To evaluate the efficacy of liposome targeting in tissues, we utilized myelinating explant cultures of dorsal root ganglia and isolated diaphragm preparations, both of which contain peripheral neurons and myelinating Schwann cells. In these models, we detected preferential liposome uptake into neurons and glial cells in comparison to surrounding muscle tissue. Furthermore, in vivo liposome administration by intramuscular or intravenous injection confirmed that the particles were delivered to myelinated peripheral nerves. Within the CNS, we detected the liposomes in choroid epithelium, but not in myelinated white matter regions or in brain parenchyma. The described nanoparticles represent a novel neurophilic delivery vehicle for targeting small therapeutic compounds, biological molecules, or imaging reagents into peripheral neurons and Schwann cells, and provide a major advancement toward developing effective therapies for peripheral neuropathies.

A reliable in vitro model for studying peripheral nerve myelination in mouse

The rat dorsal root ganglia (DRG) model is a long-standing in vitro model for analysis of myelination in the peripheral nervous system. For performing systematic, high throughput analysis with transgenic animals, a simplified BL6 mouse protocol is indispensable.Here we present a stable and reliable protocol for myelinating co-cultures producing a high myelin ratio using cells from C57BL/6 mice. As an easy accessible and operable method, Sudan staining proved to be efficient in myelin detection for fixed cultures. Green fatty acid stain turned out to be highly reliable for analysis of the dynamic biological processes of myelination in vital cultures. Once myelinated we were able to induce demyelination by the addition of forskolin into the model system. In addition, we provide an optimised rat DRG protocol with significantly improved myelin ratio and a comparison of the protocols presented.Our results strengthen the value of ex vivo myelination models in neurobiology.

Reversing hypomyelination in BACE1‐null mice with Akt‐DD overexpression

β-Site amyloid precursor protein convertase enzyme 1 (BACE1), a type I transmembrane aspartyl protease required to cleave amyloid precursor protein for releasing a toxic amyloid peptide, also cleaves type I and type III neuregulin-1 (Nrg-1). BACE1 deficiency in mice causes hypomyelination during development and impairs remyelination if injured. In BACE1-null mice, the abolished cleavage of neuregulin-1 by BACE1 is speculated to cause reduced myelin sheath thickness in both the central nervous system and peripheral nervous system because reduced cleavage of Nrg-1 correlates with reduced Akt phosphorylation, a downstream signaling molecule of the Nrg-1/ErbB pathway. Here we tested specifically whether increasing Akt activity alone in oligodendrocytes would be sufficient to reverse the hypomyelination phenotype in BACE1-null mice. BACE1-null mice were bred with transgenic mice expressing constitutively active Akt (Akt-DD; mutations with D(308)T and D(473)S) in oligodendrocytes. Relative to littermate BACE1-null controls, BACE1(-/-)/Akt-DD mice exhibited enhanced expression of myelin basic protein and promoter of proteolipid protein. The elevated expression of myelin proteins correlated with a thicker myelin sheath in optic nerves; comparison of quantified g ratios with statistic significance was used to confirm this reversion. However, it appeared that myelin sheath thickness in the sciatic nerves was not increased in BACE1(-/-)/Akt-DD mice, as the g ratio was not significantly different from the control. Hence, increased Akt activity in BACE1-null myelinating cells only compensates for the loss of BACE1 activity in the central nervous system, which is consistent with the observation that overexpression of Akt-DD in Schwann cells did not induce hypermyelination. Our results suggest that signaling activity other than Akt may also contribute to proper myelination in peripheral nerves.

Involvement of early growth response-2 (Egr-2) in lipopolysaccharide-induced neuroinflammation

Early growth response-2 (Egr-2) protein is a transcription factor, which belongs to Egr family which involve in modulating the peripheral immune response, by means of the induction of differentiation of lymphocyte precursors, activation of T and B cells. Egr-2 plays essential roles in peripheral nerve myelination, adipogenesis, tissue repair and fibrosis, immune tolerance; however, its regulation and role in central nervous system (CNS) remain poorly understood. In contrast to Egr-1, which has been extensively investigated, the regulation and function of Egr-2 remains less well characterized. To elaborate whether Egr-2 was involved in CNS injury, we performed a neuroinflammatory model by lipopolysaccharide (LPS) lateral ventral injection in adult rats. Egr-2 expression was strongly induced in active glia cells (astrocytes and microglias) in inflamed brain cortex. In vitro studies indicated that the upregulation of Egr-2 may be involved in the subsequent glia cellular activation following LPS exposure; and knock down of Egr-2 in primary mixed glial cultures (MGC) by siRNA showed that Egr-2 promoted the synthesis of TNF-α. Collectively, these results suggested Egr-2 may be important in host defense in CNS immune response, which might provide a potential target to the treatment of neuroinflammation.

Analysis of Association of Deletion in the Repeat Region of the Periaxin Gene With Late Onset Motor Neuropathy

Background: Charcot-Marie-Tooth Disease (CMT) represents a heterogeneous group of disorders affecting the peripheral nervous system. The protein encoded by the periaxin (PRX) gene has a functional role in the maintenance of peripheral nerve myelin. Mutations in the PRX gene have been identified in autosomal recessive forms of Dejerine-Sottas neuropathy and Charcot Marie Tooth disease type 4F. Both of these conditions are characterized by early onset of a demyelinating neuropathy. Methods: We report two unrelated patients, a Caucasian American and an Asian American patient with late onset progressive neuropathy. We also ascertained family members of the Asian American patient for clinical and genetic evaluation. Results: We report heterozygous deletions in the repeat region of the PRX gene ; the Caucasian patient developed symptoms as a teenager and has a 78 base pair deletion. The Asian patient became symptomatic in his forties and has a 15 base pair deletion and the same deletion was also identified in two other siblings with neuropathy. Both deletion mutations involve the repeat region in exon 7 of the PRX gene . In both patients, electrophysiological analysis demonstrates a predominantly motor neuropathy with demyelinating features. Conclusions: This is the first report of deletions involving the repeat region in exon 7 of the PRX gene . We present epidemiological data and discuss the possible significance of the association of these deletion mutations with neuropathy. d oi: http://dx.doi.org/10.4021/jnr154w

Syringomyelia Coexisting With Guillain-Barre Syndrome

Guillain-Barre syndrome (GBS) and syringomyelia are diseases of different entities. GBS is an acute post-infectious autoimmune disease which is mediated by autoantibodies against the myelin of peripheral nerves. Syringomyelia is a chronic disease characterized by a cavity extending longitudinally inside the spinal cord. A 67-year-old man is being hospitalized due to severe numbness and ascending weakness in all limbs. On neurological examination, the motor power of all limbs are decreased and show absence of deep tendon reflexes (DTRs). The patient is being diagnosed with GBS on the basis of the acute clinical course, nerve conduction studies of segmental demyelinating polyneuropathy, and a finding of albuminocytologic dissociation in the cerebrospinal fluid. The patient is presented with a new set of symptoms thereafter, which composes of sensory changes in the upper extremities, the urinary dysfunction including frequency and residual urine, spastic bilateral lower extremities, and increased reflexes of the knee and the biceps at follow-up examinations. The spinal magnetic resonance imaging in the sagittal section revealed a syrinx cavity between the fifth cervical and the first thoracic vertebral segment in the cord. The somatosensory evoked potential show sensory pathway defects between both the brachial plexus and the brain stem. Thus, this patient is being diagnosed with both GBS and syringomyelia. We report a case of symptomatic syringomyelia coexisting with GBS. Since the GBS is presented with a progressive muscle weakness and reduced DTRs, the muscle weakness and stiffness in the extremities suggests a concurrent syringomyelia might be easily overlooked.

Schwann cell myelination requires integration of laminin activities

Laminins promote early stages of peripheral nerve myelination by assembling basement membranes (BMs) on Schwann cell surfaces, leading to activation of β1 integrins and other receptors. The BM composition, structural bonds and ligands needed to mediate this process, however, are not well understood. Mice hypomorphic for laminin γ1-subunit expression that assembled endoneurial BMs with reduced component density exhibited an axonal sorting defect with amyelination but normal Schwann cell proliferation, the latter unlike the null. To identify the basis for this, and to dissect participating laminin interactions, LAMC1 gene-inactivated dorsal root ganglia were treated with recombinant laminin-211 and -111 lacking different architecture-forming and receptor-binding activities, to induce myelination. Myelin-wrapping of axons by Schwann cells was found to require higher laminin concentrations than either proliferation or axonal ensheathment. Laminins that were unable to polymerize through deletions that removed critical N-terminal (LN) domains, or that lacked cell-adhesive globular (LG) domains, caused reduced BMs and almost no myelination. Laminins engineered to bind weakly to α6β1 and/or α7β1 integrins through their LG domains, even though they could effectively assemble BMs, decreased myelination. Proliferation depended upon both integrin binding to LG domains and polymerization. Collectively these findings reveal that laminins integrate scaffold-forming and cell-adhesion activities to assemble an endoneurial BM, with myelination and proliferation requiring additional α6β1/α7β1-laminin LG domain interactions, and that a high BM ligand/structural density is needed for efficient myelination.

Clinical features of CIDP with LM1-associated antibodies

BackgroundLM1 is the predominant glycolipid in human peripheral nerve myelin and antibodies to LM1 and LM1-containing ganglioside complexes are detected in some patients with chronic inflammatory demyelinating polyneuropathy (CIDP). The...

An Unusual Mass Filling Within the Middle Meatus

Schwannoma is a benign tumor that originates from sheath of myelinated peripheral nerves, rarely seen at the nasal cavity and paranasal sinuses. Symptoms of this tumor are nonspecific, and diagnosis is often made only after histological examination. Schwannoma is radioresistant, and chemotherapy is not effective, so surgical resection is the only curative treatment for this tumor. Endoscopic sinus surgery was the first choice for this case because of its definite origin and being easy to remove for complete excision. We present a patient with schwannoma who underwent an endonasal endoscopic approach for complete resection.

Production and crystallization of a panel of structure-based mutants of the human myelin peripheral membrane protein P2.

The myelin sheath is a multilayered membrane that surrounds and insulates axons in the nervous system. One of the proteins specific to the peripheral nerve myelin is P2, a protein that is able to stack lipid bilayers. With the goal of obtaining detailed information on the structure-function relationship of P2, 14 structure-based mutated variants of human P2 were generated and produced. The mutants were designed to potentially affect the binding of lipid bilayers by P2. All mutated variants were also crystallized and preliminary crystallographic data are presented. The structural data from the mutants will be combined with diverse functional assays in order to elucidate the fine details of P2 function at the molecular level.

Fingolimod Impedes Schwann Cell–Mediated Myelination

Fingolimod (FTY720), a first-in-class sphingosine-1-phosphate (S1P) receptor agonist, is a recently approved drug for treating relapsing multiple sclerosis. Experimental evidence suggests that FTY720 not only exhibits anti-inflammatory properties but also promotes myelination in the central nervous system by direct interaction with oligodendrocytes. To assess the effects of FTY720 on Schwann cells (SCs) and peripheral nerve myelination. Receptor expression studies and myelination were investigated in primary rat SCs and rat neuronal/SC cocultures. Cells were treated with physiologically relevant concentrations of the active phosphorylated form of FTY720 (FTY720P). In addition, S1P receptor expression was corroborated in human and rat peripheral nerve tissue sections. Schwann cells express all known S1P receptors on the RNA level, not altered by FTY720P. In the myelination model, treatment with FTY720P resulted in a significant reduction of quantitative myelin formation. FTY720P induced reactive oxygen species in SCs associated with apoptosis of these cells, as demonstrated by the detection of cysteine aspartic acid–specific protease 3 and 7, as well as terminal deoxynucleotidyl transferase dUTP nick-end labeling. This effect was dependent of S1P signaling because the blocking of S1P receptors ameliorated reactive oxygen species production, SC apoptosis, and myelin loss. FTY720P at greater concentrations induces apoptosis in SCs and may interfere with peripheral nerve myelination.

A Rare Cause of Neuropathy and Failure to Thrive in a Chronic Hepatitis C Patient

Purpose: A 51-year-old African American gentleman with a history of Type 2 Diabetes and treatment naïve Hepatitis C presented with worsening thrombocytopenia, an involuntary weight loss, numbness and progressive weakness in both the upper and lower extremities. He also had difficulty ambulating with a recent onset of recurrent falls for the past 3 months and a failure to thrive. Pertinent laboratory evaluation revealed a platelet count of 80,000/mm3, a normal CPK, normal Vitamin D, B12, Folate, as well as cryoglobulin level. The patient was thought to have AIDS, but antibodies and viral loads were negative on multiple occasions. Malignancy was considered likely, but an MRI of the brain and spine, CT scan of the chest, abdomen and pelvis, and an upper and lower GI series were all negative. Urine evaluation revealed a protein of 29.0 mg/dl, but a Serum Protein Electrophoresis showed no M spike or light chains. CSF evaluation to rule out Guillian Barre revealed 190 mg/dL protein without evidence of cytoalbuminic dissociation. The patient's Hepatitis C levels was found to be over 100 million, and the patient did not have evidence of cirrhosis. EMG to evaluate the patient's numbness and weakness were consistent with diabetic peripheral neuropathy, but surprisingly revealed demyelination. The demyelination pattern on EMG revealed that the patient had Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) explaining his numbness and weakness. The patient's numbness and weakness responded well to corticosteroid and IV IgG treatment. Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) is a highly treatable, yet underdiagnosed acquired, immune mediated group of related polyneuropathies affecting the peripheral nerve myelin and spinal nerve roots. It runs a chronic course (usually >8 weeks) and is associated with inflammation with demyelination as a consistent feature. CIDP is also under-recognized in association with Hepatitis C and there are only a few cases reported in the literature. The majority of reported cases in the literature of CIDP occurred after PEG Interferon treatment of Hepatitis C. However, there is a paucity in the literature regarding Hepatitis C induced CIDP. Our case is one of the first to report CIDP development from Hepatitic C viremia. We also stress the importance of early recognition and treatment of CIDP. It is also essential to differentiate CIDP from sensory motor diabetic polyneuropathy, Hepatitis C induced neuropathy, and cryoglobulinema. Providers should have a higher suspicion for CIDP in Hepatitis C patients with disabling neuropathy and profound weakness.

G.P.86 X-linked Charcot–Marie–Tooth disease with c.22A&gt;C missense mutation in the GJB1 gene in Koreans

<h2>Abstract</h2> X-linked Charcot–Marie–Tooth disease (CMT1X) is caused by gap junction beta 1 (GJB1) gene mutations, which encodes the connexin 32. Connexin 32 is an integral transmembrane protein expressed in peripheral nerve myelin. The frequency of CMT1X varies among different ethnic groups. The frequency in Koreans is low compared with those in Europeans. Herein we present one CMT1X patient with missense mutation in the GJB1 gene. The 27-year-old male presented with complaints of slowly progressive weakness beginning in the distal leg muscles. He had walked with waddling gait ever since he had started walking at 2years of age. He felt a weak hand grip around 8years of age. He could not run and have numbness on toe tips after 18years old. The family history revealed a more severe disease phenotype in affected males compared with affected females. Physical examination showed pes cavus, wasting of muscles below knee, and intrinsic hand muscle atrophy. Neurological examination demonstrated predominantly distal muscle weakness in the lower and upper limbs, decreased pinprick sensation in stocking-glove pattern, and areflexia. Electrophysiological study revealed sensori-motor polyneuropathy, but did not suggest sufficient evidence of demyelination or axonal degeneration. Gene analysis identified c.22A>C Missense Mutation in the GJB1 gene. We report a CMT1X patient having typical X-linked dominant inheritance and missense mutation in the GJB1 gene.

The Palmitoylation State of PMP22 Modulates Epithelial Cell Morphology and Migration

PMP22 (peripheral myelin protein 22), also known as GAS 3 (growth-arrest-specific protein 3), is a disease-linked tetraspan glycoprotein of peripheral nerve myelin and constituent of intercellular junctions in epithelia. To date, our knowledge of the post-translational modification of PMP22 is limited. Using the CSS-Palm 2.0 software we predicted that C85 (cysteine 85), a highly conserved amino acid located between the second and third transmembrane domains, is a potential site for palmitoylation. To test this, we mutated C85S (C85 to serine) and established stable cells lines expressing the WT (wild-type) or the C85S-PMP22. In Schwann and MDCK (Madin–Darby canine kidney) cells mutating C85 blocked the palmitoylation of PMP22, which we monitored using 17-ODYA (17-octadecynoic acid). While palmitoylation was not necessary for processing the newly synthesized PMP22 through the secretory pathway, overexpression of C85S-PMP22 led to pronounced cell spreading and uneven monolayer thinning. To further investigate the functional significance of palmitoylated PMP22, we evaluated MDCK cell migration in a wound-healing assay. While WT-PMP22 expressing cells were resistant to migration, C85S cells displayed lamellipodial protrusions and migrated at a similar rate to vector control. These findings indicate that palmitoylation of PMP22 at C85 is critical for the role of the protein in modulating epithelial cell shape and motility.

Gene expression patterns specific to the regenerating limb of the Mexican axolotl

SummarySalamander limb regeneration is dependent upon tissue interactions that are local to the amputation site. Communication among limb epidermis, peripheral nerves, and mesenchyme coordinate cell migration, cell proliferation, and tissue patterning to generate a blastema, which will form missing limb structures. An outstanding question is how cross-talk between these tissues gives rise to the regeneration blastema. To identify genes associated with epidermis-nerve-mesenchymal interactions during limb regeneration, we examined histological and transcriptional changes during the first week following injury in the wound epidermis and subjacent cells between three injury types; 1) a flank wound on the side of the animal that will not regenerate a limb, 2) a denervated limb that will not regenerate a limb, and 3) an innervated limb that will regenerate a limb. Early, histological and transcriptional changes were similar between the injury types, presumably because a common wound-healing program is employed across anatomical locations. However, some transcripts were enriched in limbs compared to the flank and are associated with vertebrate limb development. Many of these genes were activated before blastema outgrowth and expressed in specific tissue types including the epidermis, peripheral nerve, and mesenchyme. We also identified a relatively small group of transcripts that were more highly expressed in innervated limbs versus denervated limbs. These transcripts encode for proteins involved in myelination of peripheral nerves, epidermal cell function, and proliferation of mesenchymal cells. Overall, our study identifies limb-specific and nerve-dependent genes that are upstream of regenerative growth, and thus promising candidates for the regulation of blastema formation.

Homozygous deletion of an EGR2 enhancer in congenital amyelinating neuropathy

The transcription factor EGR2 is expressed in Schwann cells, where it controls peripheral nerve myelination. Mutations of EGR2 have been found in patients with congenital hypomyelinating neuropathy or Charcot-Marie-Tooth disease type 1D. In a patient with congenital amyelinating neuropathy, we observed pathological abnormalities recapitulating the peripheral nervous system phenotype of homozygous Egr2-null mice. This patient, born from consanguineous parents, showed no EGR2 immunoreactivity in Schwann cells and harbored a homozygous 10.7-kilobase-long deletion encompassing a myelin-specific enhancer of EGR2. This regulatory mutation is the first genetic abnormality associated with congenital amyelinating neuropathy in humans.

Regulation of the bovine SCD5 promoter by EGR2 and SREBP1

In rodents, the transcription factors early growth response 2 (EGR2) and sterol regulatory element binding protein 1a (SREBP1a) regulate transcription of the stearoyl-CoA desaturase 2 (SCD2) gene during peripheral nerve myelination, which may be important for synthesis of the lipid component of myelin. Most non-rodent genomes do not contain the SCD2 gene, but rather express SCD5 in brain and nervous tissues. In this paper, we asked whether bovine SCD5 is regulated in a similar manner to rodent SCD2. Expression of EGR2 did not result in an increase in endogenous SCD5 mRNA expression in JEG3 cells, but did result in activation of truncated bovine SCD5 promoter luciferase reporter constructs. Similar results were obtained with expression of the active form of SREBP1a; however, unlike rodent SCD2, there was no synergistic activation of the bovine SCD5 promoter reporters when EGR2 and SREBP1a were co-expressed. Mutation of the putative EGR2 binding site in the SCD5 promoter abolished activation by SREBP1a, suggesting that EGR2 and SREBP1a bind to the same site in the SCD5 promoter. Finally, we have identified a region of the bovine SCD5 promoter between 505 and 305 base pairs upstream of the transcriptional start site that appears to be important for maintaining basal levels of transcription of this gene. While it appears that there are some differences between the regulation of rodent SCD2 and bovine SCD5, the promoters of both genes can be activated by EGR2 and SREBP1a. This is the first report of potential regulators of SCD5 transcription.