RESUMO
The transcription factor Zic3 is required for maintenance of ESC pluripotency. By genome-wide chromatin immunoprecipitation (ChIP-chip) in ESCs, we have identified 379 direct Zic3 targets, many of which are functionally associated with pluripotency, cell cycle, proliferation, oncogenesis, and early embryogenesis. Through a computational analysis of Zic3 target sequences, we have identified a novel Zic3 consensus binding motif (5'-CC(C)/(T) GCTGGG-3'). ChIP results and in vitro DNA binding assays revealed that Zic3 binds with high affinity and specificity on the Nanog promoter. Here, we demonstrate that Zic3 functions as a transcriptional activator of the Nanog promoter in three ways: (a) Nanog transcript levels are sustained with Zic3 overexpression in differentiating ESCs, (b) Zic3 depletion in ESCs downregulates Nanog promoter activity, and (c) Zic3 overexpression leads to increased Nanog promoter activity. Furthermore, the activity of a mutant Nanog promoter with ablated Oct4/Sox2 binding is rescued by Zic3 overexpression to nearly wild-type levels. This indicates that Nanog is a positive transcriptional target of Zic3 in a mechanism that is independent of Oct4/Sox2 binding. Hence, we demonstrate an important pathway for regulation of Nanog expression in pluripotent ESCs through direct activation by Zic3.
Assuntos
Células-Tronco Embrionárias/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Regiões Promotoras Genéticas/genética , Fatores de Transcrição/metabolismo , Animais , Sítios de Ligação , Linhagem Celular , Imunoprecipitação da Cromatina , Ensaio de Desvio de Mobilidade Eletroforética , Camundongos , Proteína Homeobox Nanog , Reação em Cadeia da Polimerase , Ligação Proteica , Interferência de RNA , Fatores de Transcrição/genéticaRESUMO
Early studies of genetic predisposition due to the BRCA1 and BRCA2 genes have focused largely on sequence alterations, but it has now emerged that 4-28% of inherited mutations in the BRCA genes may be due to large genomic rearrangements of these genes. However, to date, there have been relatively few studies of large genomic rearrangements in Asian populations. We have conducted a full sequencing and large genomic rearrangement analysis (using Multiplex Ligation-dependent Probe Amplification, MLPA) of 324 breast cancer patients who were selected from a multi-ethnic hospital-based cohort on the basis of age of onset of breast cancer and/or family history. Three unrelated individuals were found to have large genomic rearrangements: 2 in BRCA1 and 1 in BRCA2, which accounts for 2/24 (8%) of the total mutations detected in BRCA1 and 1/23 (4%) of the mutations in BRCA2 detected in this cohort. Notably, the family history of the individuals with these mutations is largely unremarkable suggesting that family history alone is a poor predictor of mutation status in Asian families. In conclusion, this study in a multi-ethnic (Malay, Chinese, Indian) cohort suggests that large genomic rearrangements are present at a low frequency but should nonetheless be included in the routine testing for BRCA1 and BRCA2.
Assuntos
Povo Asiático/genética , Proteína BRCA1/genética , Proteína BRCA2/genética , Neoplasias da Mama Masculina/genética , Neoplasias da Mama/genética , Rearranjo Gênico , Neoplasias Ovarianas/genética , Adulto , Idade de Início , Neoplasias da Mama/etnologia , Neoplasias da Mama Masculina/etnologia , Pontos de Quebra do Cromossomo , Éxons , Feminino , Predisposição Genética para Doença , Humanos , Malásia/epidemiologia , Masculino , Pessoa de Meia-Idade , Neoplasias Ovarianas/etnologia , Linhagem , Fenótipo , Medição de Risco , Fatores de Risco , Deleção de SequênciaRESUMO
Embryonic stem (ES) cell pluripotency is dependent upon sustained expression of the key transcriptional regulators Oct4, Nanog, and Sox2. Dissection of the regulatory networks downstream of these transcription factors has provided critical insight into the molecular mechanisms that regulate ES cell pluripotency and early differentiation. Here we describe a role for Zic3, a member of the Gli family of zinc finger transcription factors, in the maintenance of pluripotency in ES cells. We show that Zic3 is expressed in ES cells and that this expression is repressed upon differentiation. The expression of Zic3 in pluripotent ES cells is also directly regulated by Oct4, Sox2, and Nanog. Targeted repression of Zic3 in human and mouse ES cells by RNA interference-induced expression of several markers of the endodermal lineage. Notably, the expression of Nanog, a key pluripotency regulator and repressor of extraembryonic endoderm specification in ES cells, was significantly reduced in Zic3 knockdown cells. This suggests that Zic3 may prevent endodermal marker expression through Nanog-regulated pathways. Thus our results extend the ES cell transcriptional network beyond Oct4, Nanog, and Sox2, and further establish that Zic3 plays an important role in the maintenance of pluripotency by preventing endodermal lineage specification in embryonic stem cells.