Article

Expression patterns of MLC1 protein in the central and peripheral nervous systems

Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Institute for Research in Biomedicine, Barcelona Science Park, Josep Samitier 1-5. Barcelona, E-08028, Spain.
Neurobiology of Disease (Impact Factor: 5.2). 07/2007; 26(3):532-45. DOI: 10.1016/j.nbd.2007.01.016
Source: PubMed

ABSTRACT Mutations in MLC1 cause megalencephalic leukoencephalopathy with subcortical cysts (MLC), a disorder characterized clinically by macrocephaly, deterioration of motor functions, epilepsy and mental decline. Recent studies have detected MLC1 mRNA and protein in astroglial processes. In addition, our group previously reported MLC1 expression in some neurons in the adult mouse brain. Here we performed an exhaustive study of the expression pattern of MLC1 in the developing mouse brain by means of optic and electron microscopy. In the central nervous system, MLC1 was detected mainly in axonal tracts early in development. In addition, MLC1 was also observed in the peripheral nervous system and in several sensory epithelia, as retina or saccula maculae. Post-embedding immunogold experiments indicated that MLC1 is localized in astrocyte-astrocyte junctions, but not in the perivascular membrane, indicating that MLC1 is not a component of the dystrophin-glycoprotein complex. In neurons, MLC1 is located at the plasma membrane and vesicular structures. Our data provide a mouse MLC1 expression map that could be useful to understand the phenotype of MLC patients, and suggested that MLC disease is caused by an astrocytic and a neuronal dysfunction.

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    • "MLC1 is homologous with carrier proteins and is confined to the plasma membrane, which indicates that it may regulate substance translocation across the cell membrane [3], [7]. Besides, it has not yet been determined whether MLC1 is localized in membrane contact regions between endothelial cells and glial cells or between different kinds of glial cells [8]–[10]. "
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    ABSTRACT: Megalencephalic leukoencephalopathy with subcortical cysts (MLC, MIM# 604004) is an autosomal recessive inherited disease mostly resulting from MLC1 mutations. In this study, we finished the functional analysis of MLC1 mutations identified recently in Chinese patients, including five newly described missense mutations (R22Q, A32V, G73E, A275T, Y278H), one known nonsense mutation (Y198X), and two known missense mutations (S69L, T118M). We found MLC1(wt) was localized to the cell periphery, whereas mutant R22Q, A32V, G73E, S69L and T118M were trapped in the lumen of endoplasmic reticulum (ER) when we transfected the wild-type and mutant MLC1 in U373MG cells. Compared to wild type, the mutant G73E, T118M, Y198X and A275T transcript decreased and all mutants except R22Q had lower protein expression in transfected U373MG cells. Therefore, we propose that all these eight MLC1 mutations had functional effect either on their protein/mRNA expression, or on their intracellular protein localization, or both.
    PLoS ONE 03/2012; 7(3):e33087. DOI:10.1371/journal.pone.0033087 · 3.23 Impact Factor
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    • "Posteriorment , en un estudi detallat del desenvolupament de ratolí , es va descriure l ' expressió de la proteïna MLC1 en tractes axonals als primers estadis de desenvolupament en el sistema nerviós central ( SNC ) , però no en la mielina en estadis posteriors ( Teijido et al . , 2007 ) . MLC1 s ' expressava en el sistema nerviós perifèric ( SNP ) , concretament en l ' epiteli sensorial , en l ' oïda interna , en la retina , en el nervi òptic i ciàtic , i en la medul·la . També es va precisar la localització de MLC1 a la membrana de contacte entre astròcits . Aquests resultats demostraven que MLC1 no formava part del"
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    • "For example, the thiamine transporter, Slc19a2 [32], [50], the choline and acetylcholine transporters, Slc5a7 and Slc18a3 [51], and the membrane protein Vamp1 were normally expressed in the inner hair cells of the mouse but their levels were consistently lower in the Igf1−/− cochlea. In contrast Mlc1, which encodes a protein located in the afferent fibers of the inner hair cells [52], was expressed at higher levels. These data support the idea that IGF-I is a key molecule for the maturation of the auditory neurons and the refinement of the synaptic connections at the inner hair cells. "
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    ABSTRACT: Insulin-like growth factor-I (IGF-I) provides pivotal cell survival and differentiation signals during inner ear development throughout evolution. Homozygous mutations of human IGF1 cause syndromic sensorineural deafness, decreased intrauterine and postnatal growth rates, and mental retardation. In the mouse, deficits in IGF-I result in profound hearing loss associated with reduced survival, differentiation and maturation of auditory neurons. Nevertheless, little is known about the molecular basis of IGF-I activity in hearing and deafness. A combination of quantitative RT-PCR, subcellular fractionation and Western blotting, along with in situ hybridization studies show IGF-I and its high affinity receptor to be strongly expressed in the embryonic and postnatal mouse cochlea. The expression of both proteins decreases after birth and in the cochlea of E18.5 embryonic Igf1(-/-) null mice, the balance of the main IGF related signalling pathways is altered, with lower activation of Akt and ERK1/2 and stronger activation of p38 kinase. By comparing the Igf1(-/-) and Igf1(+/+) transcriptomes in E18.5 mouse cochleae using RNA microchips and validating their results, we demonstrate the up-regulation of the FoxM1 transcription factor and the misexpression of the neural progenitor transcription factors Six6 and Mash1 associated with the loss of IGF-I. Parallel, in silico promoter analysis of the genes modulated in conjunction with the loss of IGF-I revealed the possible involvement of MEF2 in cochlear development. E18.5 Igf1(+/+) mouse auditory ganglion neurons showed intense MEF2A and MEF2D nuclear staining and MEF2A was also evident in the organ of Corti. At P15, MEF2A and MEF2D expression were shown in neurons and sensory cells. In the absence of IGF-I, nuclear levels of MEF2 were diminished, indicating less transcriptional MEF2 activity. By contrast, there was an increase in the nuclear accumulation of FoxM1 and a corresponding decrease in the nuclear cyclin-dependent kinase inhibitor p27(Kip1). We have defined the spatiotemporal expression of elements involved in IGF signalling during inner ear development and reveal novel regulatory mechanisms that are modulated by IGF-I in promoting sensory cell and neural survival and differentiation. These data will help us to understand the molecular bases of human sensorineural deafness associated to deficits in IGF-I.
    PLoS ONE 01/2010; 5(1):e8699. DOI:10.1371/journal.pone.0008699 · 3.23 Impact Factor
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