RESUMEN
FOXP2, a forkhead box-containing transcription factor, forms homo- or hetero-dimers with FOXP family members and localizes to the nucleus, while FOXP2(R553H), which contains a mutation related to speech/language disorders, features reduced DNA binding activity and both cytoplasmic and nuclear localization. In addition to being a loss-of-function mutation, it is possible that FOXP2(R553H) also may act as a gain-of-function mutation to inhibit the functions of FOXP2 isoforms including FOXP2Ex10+ lacking forkhead domain. Foxp2(R552H) knock-in mouse pups exhibit impaired ultrasonic vocalization and poor dendritic development in Purkinje cells. However, expressions of Foxp2 isoforms in the developing Purkinje are unclear. The appearance of 'apical cytoplasmic swelling' (mitochondria-rich regions that are the source of budding processes) correlates with dendritic development of Purkinje cells. In the present study, we focused on Foxp2 isoforms localizing to the apical cytoplasmic swelling and identified two isoforms lacking forkhead domain: Foxp2Ex12+ and Foxp2Ex15. They partly localized to the membrane fraction that includes mitochondria. Foxp2Ex12+ mainly localized to the apical cytoplasmic swelling in early developing Purkinje cells at the stellate stage (P2-P4). Mitochondrial localization of Foxp2Ex12+ in Purkinje cells was confirmed by immune-electron microscopic analysis. Foxp2Ex12+ may play a role in dendritic development in Purkinje cells.
Asunto(s)
Cerebelo/citología , Cerebelo/crecimiento & desarrollo , Factores de Transcripción Forkhead/genética , Regulación del Desarrollo de la Expresión Génica/genética , Mitocondrias/metabolismo , Células de Purkinje/ultraestructura , Proteínas Represoras/genética , Factores de Edad , Animales , Animales Recién Nacidos , Arginina/genética , Calbindinas , Citocromos c/metabolismo , Citoplasma/metabolismo , Dendritas/metabolismo , Dendritas/ultraestructura , Feto , Factores de Transcripción Forkhead/clasificación , Histidina/genética , Humanos , Ratones , Ratones Transgénicos , Microscopía Inmunoelectrónica , Mutación/genética , Isoformas de Proteínas/genética , Receptores de Hormona Liberadora de Corticotropina/metabolismo , Proteínas Represoras/clasificación , Proteína G de Unión al Calcio S100/metabolismo , Fracciones Subcelulares/metabolismo , Ultrasonido , Vocalización Animal/fisiologíaRESUMEN
Although a mutation (R553H) in the forkhead box (FOX)P2 gene is associated with speech/language disorder, little is known about the function of FOXP2 or its relevance to this disorder. In the present study, we identify the forkhead nuclear localization domains that contribute to the cellular distribution of FOXP2. Nuclear localization of FOXP2 depended on two distally separated nuclear localization signals in the forkhead domain. A truncated version of FOXP2 lacking the leu-zip, Zn2+ finger, and forkhead domains that was observed in another patient with speech abnormalities demonstrated an aggregated cytoplasmic localization. Furthermore, FOXP2 (R553H) mainly exhibited a cytoplasmic localization despite retaining interactions with nuclear transport proteins (importin alpha and beta). Interestingly, wild type FOXP2 promoted the transport of FOXP2 (R553H) into the nucleus. Mutant and wild type FOXP2 heterodimers in the nucleus or FOXP2 R553H in the cytoplasm may underlie the pathogenesis of the autosomal dominant speech/language disorder.