RESUMO
Mutations in GJB1, the gene encoding the gap junction protein connexin32 (Cx32), cause X-linked Charcot-Marie-Tooth disease (CMTX). We compared the localization of CMTX mutants that affect different domains of Cx32, by expressing them in HeLa cells. Mutants were localized to the endoplasmic reticulum (M34K, N205I, and Y211x), in the Golgi apparatus without reaching the cell membrane (M34T, V38M, A40V, R75Q, R75P, R75W, and C217x), in the Golgi apparatus but also forming rare small gap junction-like plaques (M34I, M34V, and V37M), or mainly on the cell membrane, forming gap junction-like plaques (V35M, I213V, R219C, R219H, R220G, R230C, R230L, R238H, L239I, and S281x). Selected mutants expressed in cultured rat Schwann cells showed localization similar to that in HeLa cells. Thus, many CMTX mutants have trafficking abnormalities, whereas the carboxy-terminus mutants reach the cell membrane and probably cause disease through other mechanisms.
Assuntos
Doença de Charcot-Marie-Tooth/metabolismo , Conexinas/genética , Neurônios/metabolismo , Cromossomo X , Sequência de Aminoácidos , Animais , Doença de Charcot-Marie-Tooth/genética , Conexinas/química , Junções Comunicantes/metabolismo , Células HeLa , Humanos , Dados de Sequência Molecular , Mutação de Sentido Incorreto , Neurônios/citologia , Estrutura Terciária de Proteína , Transporte Proteico/fisiologia , Ratos , Células de Schwann/citologia , Células de Schwann/metabolismo , Nervo Isquiático/citologia , Proteína beta-1 de Junções ComunicantesRESUMO
Despite the importance of myelinating Schwann cells in health and disease, little is known about the genetic mechanisms underlying their development. The POU domain transcription factor pou3f1 (Tst-1, SCIP, Oct-6) is required for the normal differentiation of myelinating Schwann cells, but its precise role requires identification of the genes that it regulates. Here we report the isolation of six genes whose expression is reduced in the absence of pou3f1. Only one of these genes, the fatty acid transport protein P2, was known previously to be expressed in Schwann cells. The LIM domain proteins cysteine-rich protein-1 (CRP1) and CRP2 are expressed in sciatic nerve and induced by forskolin in cultured Schwann cells, but only CRP2 requires pou3f1 for normal expression. pou3f1 appears to require the claw paw gene product for activation of at least some of its downstream effector genes. Expression of the novel Schwann cell genes after nerve injury suggests that they are myelin related. One of the genes, tramdorin1, encodes a novel amino acid transport protein that is localized to paranodes and incisures. Our results suggest that pou3f1 functions to activate gene expression in the differentiation of myelinating Schwann cells.
Assuntos
Proteínas Aviárias , Regulação para Baixo/fisiologia , Perfilação da Expressão Gênica , Nervo Isquiático/metabolismo , Neuropatia Ciática/metabolismo , Fatores de Transcrição/deficiência , Proteínas Adaptadoras de Transdução de Sinal , Sistemas de Transporte de Aminoácidos/fisiologia , Animais , Proteína beta Intensificadora de Ligação a CCAAT/metabolismo , Proteínas de Transporte/metabolismo , Diferenciação Celular/fisiologia , Membrana Celular/metabolismo , Células Cultivadas , Colforsina/farmacologia , Citoesqueleto/metabolismo , Modelos Animais de Doenças , Regulação para Baixo/efeitos dos fármacos , Proteínas com Domínio LIM , Camundongos , Camundongos Mutantes , Bainha de Mielina/metabolismo , Fator 6 de Transcrição de Octâmero , Estrutura Terciária de Proteína/fisiologia , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Células de Schwann/citologia , Células de Schwann/efeitos dos fármacos , Células de Schwann/metabolismo , Nervo Isquiático/lesões , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
We have examined the effects of transforming growth factor beta1 (TGFbeta1) on gene expression in cultured rat Schwann cells (SCs). TGFbeta1 decreased the steady-state mRNA levels of several genes that are expressed by myelinating SCs but had varied effects on the mRNA levels of NCAM, L1, GAP-43, and p75-genes that are expressed by denervated and nonmyelinating SCs. TGFbeta1 antagonized the effects of forskolin on the mRNA levels of the transcription factors Oct-6/tst-1/SCIP and Krox20. Transcriptional run-off analysis demonstrated that the effects of TGFbeta1 on gene expression occur at least in part at the level of transcription. Thus, TGFbeta1 suppresses the expression of genes that characterize the different phenotypes of SCs, and these changes occur at least in part at a transcriptional level.