RESUMEN
Embryonic stem cells (ESCs) exhibit a unique cell cycle with a shortened G1 phase that supports their pluripotency, while apparently buffering them against pro-differentiation stimuli. In ESCs, expression of replication-dependent histones is a main component of this abbreviated G1 phase, although the details of this mechanism are not well understood. Similarly, the role of 3' end processing in regulation of ESC pluripotency and cell cycle is poorly understood. To better understand these processes, we examined mouse ESCs that lack the 3' end-processing factor CstF-64. These ESCs display slower growth, loss of pluripotency and a lengthened G1 phase, correlating with increased polyadenylation of histone mRNAs. Interestingly, these ESCs also express the τCstF-64 paralog of CstF-64. However, τCstF-64 only partially compensates for lost CstF-64 function, despite being recruited to the histone mRNA 3' end-processing complex. Reduction of τCstF-64 in CstF-64-deficient ESCs results in even greater levels of histone mRNA polyadenylation, suggesting that both CstF-64 and τCstF-64 function to inhibit polyadenylation of histone mRNAs. These results suggest that CstF-64 plays a key role in modulating the cell cycle in ESCs while simultaneously controlling histone mRNA 3' end processing.
Asunto(s)
Ciclo Celular/genética , Factor de Estimulación del Desdoblamiento/fisiología , Células Madre Embrionarias/metabolismo , Histonas/genética , Procesamiento de Término de ARN 3' , Animales , Diferenciación Celular , Línea Celular , Proliferación Celular , Células Cultivadas , Factor de Estimulación del Desdoblamiento/análisis , Factor de Estimulación del Desdoblamiento/genética , Factor de Estimulación del Desdoblamiento/metabolismo , Células Madre Embrionarias/química , Células Madre Embrionarias/citología , Histonas/metabolismo , Ratones , Células Madre Pluripotentes/metabolismo , Ribonucleoproteína Nuclear Pequeña U7/química , Ribonucleoproteína Nuclear Pequeña U7/metabolismoRESUMEN
BARD1 is a crucial partner of the breast and ovarian tumor suppressor BRCA1 required for ubiquitin ligase activity and for reciprocal stabilization in cells. We report here an alternatively spliced human BARD1 mRNA variant (BARD1DeltaRIN) isolated from a HeLa cell cDNA library. It is characterized by deletion of exons 2-6 that encode most of the RING finger domain and the entire span of ankyrin repeats. DeltaRIN transcript was detected in all breast cancer-cell lines studied although its protein expression level was low. DeltaRIN does not interact with BRCA1, whereas it interacts with and colocalizes with CstF-50 to cytoplasmic dots. Hence, a deletion variant of BARD1 occurs in cells and may play a distinct role with CstF-50.