RESUMO
Transcription factor EBF1 (early B cell factor 1) acts as a key regulator of B cell specification. The transcriptional network in which EBF1 operates has been extensively studied; however, the regulation of EBF1 function remains poorly defined. By mass spectrometric analysis of proteins associated with endogenous EBF1 in pro-B cells, we identified the nuclear import receptor Transportin-3 (Tnpo3) and found that it interacts with the immunoglobulin-like fold domain of EBF1. We delineated glutamic acid 271 of EBF1 as a critical residue for the association with Tnpo3. EBF1E271A showed normal nuclear localization; however, it had an impaired B cell programming ability in conditions of Notch signaling, as determined by retroviral transduction of Ebf1 -/- progenitors. By RNA-seq analysis of EBF1E271A-expressing progenitors, we found an up-regulation of T lineage determinants and down-regulation of early B genes, although similar chromatin binding of EBF1E271A and EBF1wt was detected in pro-B cells expressing activated Notch1. B lineage-specific inactivation of Tnpo3 in mice resulted in a block of early B cell differentiation, accompanied by a down-regulation of B lineage genes and up-regulation of T and NK lineage genes. Taken together, our observations suggest that Tnpo3 ensures B cell programming by EBF1 in nonpermissive conditions.
Assuntos
Ácido Glutâmico , Transativadores , beta Carioferinas , Animais , Camundongos , beta Carioferinas/metabolismo , Linhagem da Célula/genética , Cromatina , Imunoglobulinas/genética , Imunoglobulinas/metabolismo , Carioferinas/genética , Receptores Notch/metabolismo , Transativadores/metabolismo , Fatores de Transcrição/metabolismoRESUMO
B-cell fate determination requires the action of transcription factors that operate in a regulatory network to activate B-lineage genes and repress lineage-inappropriate genes. However, the dynamics and hierarchy of events in B-cell programming remain obscure. To uncouple the dynamics of transcription factor expression from functional consequences, we generated induction systems in developmentally arrested Ebf1-/- pre-pro-B cells to allow precise experimental control of EBF1 expression in the genomic context of progenitor cells. Consistent with the described role of EBF1 as a pioneer transcription factor, we show in a time-resolved analysis that EBF1 occupancy coincides with EBF1 expression and precedes the formation of chromatin accessibility. We observed dynamic patterns of EBF1 target gene expression and sequential up-regulation of transcription factors that expand the regulatory network at the pro-B-cell stage. A continuous EBF1 function was found to be required for Cd79a promoter activity and for the maintenance of an accessible chromatin domain that is permissive for binding of other transcription factors. Notably, transient EBF1 occupancy was detected at lineage-inappropriate genes prior to their silencing in pro-B cells. Thus, persistent and transient functions of EBF1 allow for an ordered sequence of epigenetic and transcriptional events in B-cell programming.
Assuntos
Linfócitos B/metabolismo , Epigênese Genética , Células-Tronco/metabolismo , Transativadores/metabolismo , Transcrição Gênica , Animais , Antígenos CD79/genética , Linhagem da Célula/genética , Células Cultivadas , Cromatina/metabolismo , DNA/metabolismo , Camundongos , Fator de Transcrição PAX5/metabolismo , Regiões Promotoras Genéticas , Proteínas Proto-Oncogênicas/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Earlier studies have identified transcription factors that specify B-cell fate, but the underlying mechanisms remain to be revealed. Two new studies by Miyai and colleagues (pp. 112-126) and Li and colleagues (pp. 96-111) in this issue of Genes & Development provide new and unprecedented insights into the genetic and epigenetic mechanisms that establish B-cell identity.