The TFDP1 gene coding for DP1, the heterodimeric partner of the transcription factor E2F, is a target of deregulated E2F.

The TFDP1 gene codes for the heterodimeric partner DP1 of the transcription factor E2F. E2F, principal target of the tumor suppressor pRB, plays central roles in cell proliferation by activating a group of growth-related genes. E2F also mediates tumor suppression by activating tumor suppressor genes such as ARF, an upstream activator of the tumor suppressor p53, when deregulated from pRB upon oncogenic changes.

Premature translation of the Drosophila zygotic genome activator Zelda is not sufficient to precociously activate gene expression.

Following fertilization, the unified germ cells rapidly transition to a totipotent embryo. Maternally deposited mRNAs encode the proteins necessary for this reprogramming as the zygotic genome remains transcriptionally quiescent during the initial stages of development. The transcription factors required to activate the zygotic genome are among these maternally deposited mRNAs and are robustly translated following fertilization.

Cell-type-specific chromatin occupancy by the pioneer factor Zelda drives key developmental transitions in Drosophila.

During Drosophila embryogenesis, the essential pioneer factor Zelda defines hundreds of cis-regulatory regions and in doing so reprograms the zygotic transcriptome. While Zelda is essential later in development, it is unclear how the ability of Zelda to define cis-regulatory regions is shaped by cell-type-specific chromatin architecture. Asymmetric division of neural stem cells (neuroblasts) in the fly brain provide an excellent paradigm for investigating the cell-type-specific functions of this pioneer factor.

Sequential activation of transcriptional repressors promotes progenitor commitment by silencing stem cell identity genes.

Stem cells that indirectly generate differentiated cells through intermediate progenitors drives vertebrate brain evolution. Due to a lack of lineage information, how stem cell functionality, including the competency to generate intermediate progenitors, becomes extinguished during progenitor commitment remains unclear. Type II neuroblasts in fly larval brains divide asymmetrically to generate a neuroblast and a progeny that commits to an intermediate progenitor (INP) identity.

Multilayered gene control drives timely exit from the stem cell state in uncommitted progenitors during asymmetric neural stem cell division.

Self-renewal genes maintain stem cells in an undifferentiated state by preventing the commitment to differentiate. Robust inactivation of self-renewal gene activity following asymmetric stem cell division allows uncommitted stem cell progeny to exit from an undifferentiated state and initiate the commitment to differentiate. Nonetheless, how self-renewal gene activity at mRNA and protein levels becomes synchronously terminated in uncommitted stem cell progeny is unclear.

Differential requirement for dimerization partner DP between E2F-dependent activation of tumor suppressor and growth-related genes.

The transcription factor E2F plays crucial roles in cell proliferation and tumor suppression by activating growth-related genes and pro-apoptotic tumor suppressor genes, respectively. It is generally accepted that E2F binds to target sequences with its heterodimeric partner DP. Here we show that, while knockdown of DP1 expression inhibited ectopic E2F1- or adenovirus E1a-induced expression of the CDC6 gene and cell proliferation, knockdown of DP1 and DP2 expression did not affect ectopic E2F1- or E1a-induced expression of the tumor suppressor ARF gene, an upstream activator of the tumor suppressor p53, activation of p53 or apoptosis.

Trithorax maintains the functional heterogeneity of neural stem cells through the transcription factor buttonhead.

The mechanisms that maintain the functional heterogeneity of stem cells, which generates diverse differentiated cell types required for organogenesis, are not understood. In this study, we report that Trithorax (Trx) actively maintains the heterogeneity of neural stem cells (neuroblasts) in the developing Drosophila larval brain. trx mutant type II neuroblasts gradually adopt a type I neuroblast functional identity, losing the competence to generate intermediate neural progenitors (INPs) and directly generating differentiated cells.

Earmuff restricts progenitor cell potential by attenuating the competence to respond to self-renewal factors.

Despite expressing stem cell self-renewal factors, intermediate progenitor cells possess restricted developmental potential, which allows them to give rise exclusively to differentiated progeny rather than stem cell progeny. Failure to restrict the developmental potential can allow intermediate progenitor cells to revert into aberrant stem cells that might contribute to tumorigenesis. Insight into stable restriction of the developmental potential in intermediate progenitor cells could improve our understanding of the development and growth of tumors, but the mechanisms involved remain largely unknown.

Brain tumor specifies intermediate progenitor cell identity by attenuating β-catenin/Armadillo activity.

During asymmetric stem cell division, both the daughter stem cell and the presumptive intermediate progenitor cell inherit cytoplasm from their parental stem cell. Thus, proper specification of intermediate progenitor cell identity requires an efficient mechanism to rapidly extinguish the activity of self-renewal factors, but the mechanisms remain unknown in most stem cell lineages. During asymmetric division of a type II neural stem cell (neuroblast) in the Drosophila larval brain, the Brain tumor (Brat) protein segregates unequally into the immature intermediate neural progenitor (INP), where it specifies INP identity by attenuating the function of the self-renewal factor Klumpfuss (Klu), but the mechanisms are not understood.

Failure in activation of the canonical NF-κB pathway by human T-cell leukemia virus type 1 Tax in non-hematopoietic cell lines.

Human T-cell leukemia virus type 1 (HTLV-1) Tax (Tax1) plays crucial roles in leukemogenesis in part through activation of NF-κB. In this study, we demonstrated that Tax1 activated an NF-κB binding (gpκB) site of the gp34/OX40 ligand gene in a cell type-dependent manner. Our examination showed that the gpκΒ site and authentic NF-κB (IgκB) site were activated by Tax1 in hematopoietic cell lines.

klumpfuss distinguishes stem cells from progenitor cells during asymmetric neuroblast division.

Asymmetric stem cell division balances maintenance of the stem cell pool and generation of diverse cell types by simultaneously allowing one daughter progeny to maintain a stem cell fate and its sibling to acquire a progenitor cell identity. A progenitor cell possesses restricted developmental potential, and defects in the regulation of progenitor cell potential can directly impinge on the maintenance of homeostasis and contribute to tumor initiation. Despite their importance, the molecular mechanisms underlying the precise regulation of restricted developmental potential in progenitor cells remain largely unknown.

Tumor suppressor TAp73 gene specifically responds to deregulated E2F activity in human normal fibroblasts.

Discrimination of oncogenic growth signals from normal growth signals is crucial for tumor suppression. The transcription factor E2F, the main target of pRB, plays central role in cell proliferation by activating growth-promoting genes. E2F also plays an important role in tumor suppression by activating growth-suppressive genes such as pro-apoptotic genes.

Identification of neural stem cells in the Drosophila larval brain.

The balance between self-renewal and differentiation must be tightly regulated in somatic stem cells to ensure proper tissue generation and to prevent tumorlike overgrowth. A Drosophila larval brain lobe consists of the central brain and the optic lobe and possesses three well-defined neural stem cell lineages that generate differentiated cells in a highly reproducible pattern. Unambiguous identification of various cell types in these stem cell lineages is pivotal for studying the regulation of neural stem cells and progenitor cells at a single-cell resolution.

Multicolor fluorescence RNA in situ hybridization of Drosophila brain tissue.

RNA in situ hybridization is a useful method for determining the transcriptional expression pattern of a gene when antibodies are not available. Using this technique, it is possible to assay the expression of multiple RNA species using distinct labels on RNA probes, or simultaneously examine RNA and protein localization within larval tissues. This protocol describes RNA in situ hybridization of Drosophila brain tissue.

EdU (5-ethynyl-2'-deoxyuridine) labeling of Drosophila mitotic neuroblasts.

When examining mutants that affect cell fate as a result of altered asymmetric division patterns, it is important to determine whether cells are mitotically active. Chemical labeling of newly synthesized DNA (during S-phase) by incorporation of BrdU (5-bromo-2'-deoxyuridine) is informative because this thymidine analog can be used to pulse-label dividing cells and then chased to identify the progeny of dividing cells. Such pulse-chase experiments can provide additional insight by distinguishing actively dividing cells from those that might be arrested at a mitotic checkpoint.

Immunofluorescent staining of Drosophila larval brain tissue.

The Drosophila larval brain is a well-established model for investigating the role of stem cells in development. Neuroblasts (neural stem cells) must be competent to generate many thousands of differentiated neurons through asymmetric divisions during normal development. Studies in fly neuroblasts have been instrumental in identifying how the establishment and maintenance of cell polarity influence cell fate, and they have produced a wide array of molecular cell-polarity markers.

E2F-like elements in p27(Kip1) promoter specifically sense deregulated E2F activity.

The transcription factor E2F, the main target of the RB tumor suppressor pathway, plays crucial roles not only in cell proliferation but also in tumor suppression. The cyclin-dependent kinase inhibitor p27(Kip1) gene, an upstream negative regulator of E2F, is induced by ectopically expressed E2F1 but not by normal growth stimulation that physiologically activates endogenous E2F. This suggests that the gene can discriminate between deregulated and physiological E2F activity.

Distinct E2F-mediated transcriptional program regulates p14ARF gene expression.

The tumor suppressor p14(ARF) gene is induced by ectopically expressed E2F, a positive regulator of the cell cycle. The gene is expressed at low levels in normally growing cells in contrast to high levels in varieties of tumors. How p14(ARF) gene is regulated by E2F in normally growing cells and tumor cells remains obscure.

Differential regulation of expression of the mammalian DNA repair genes by growth stimulation.

During DNA replication, DNA becomes more vulnerable to certain DNA damages. DNA repair genes involved in repair of the damages may be induced by growth stimulation. However, regulation of DNA repair genes by growth stimulation has not been analysed in detail.