Transcription factor NF-Y is involved in differentiation of R7 photoreceptor cell in Drosophila

Cell Cycle Regulation by NF-YC in Drosophila Eye Imaginal Disc: Implications for Synchronization in the Non-Proliferative Region

Cell cycle progression during development is meticulously coordinated with differentiation. This is particularly evident in the Drosophila 3rd instar eye imaginal disc, where the cell cycle is synchronized and arrests at the G1 phase in the non-proliferative region (NPR), setting the stage for photoreceptor cell differentiation. Here, we identify the transcription factor Nuclear Factor-YC (NF-YC) as a crucial player in this finely tuned progression, elucidating its specific role in the synchronized movement of the morphogenetic furrow. Depletion of NF-YC leads to extended expression of Cyclin A (CycA) and Cyclin B (CycB) from the FMW to the NPR. Notably, NF-YC knockdown resulted in decreased expression of Eyes absent (Eya) but did not affect Decapentaplegic (Dpp) and Hedgehog (Hh). Our findings highlight the role of NF-YC in restricting the expression of CycA and CycB in the NPR, thereby facilitating cell-cycle synchronization. Moreover, we identify the transcriptional cofactor Eya as a downstream target of NF-YC, revealing a new regulatory pathway in Drosophila eye development. This study expands our understanding of NF-YC's role from cell cycle control to encompass developmental processes.

Drosophila transcription factor NF-Y suppresses transcription of the lipase 4 gene, a key gene for lipid storage

The CCAAT motif-binding factor NF-Y consists of three different subunits, NF-YA, NF-YB, and NF-YC. Although it is suggested that NF-Y activity is essential for normal tissue homeostasis, survival, and metabolic function, its precise role in lipid metabolism is not clarified yet. In Drosophila, eye disc specific knockdown of Drosophila NF-YA (dNF-YA) induced aberrant morphology of the compound eye, the rough eye phenotype in adults and mutation of the lipase 4 (lip4) gene suppressed the rough eye phenotype. RNA-seq analyses with dNF-YA knockdown third instar larvae identified the lip4 gene as one of the genes that are up-regulated by the dNF-YA knockdown. We identified three dNF-Y-binding consensuses in the 5'flanking region of the lip4 gene, and a chromatin immunoprecipitation assay with the specific anti-dNF-YA IgG demonstrated dNF-Y binding to this genomic region. The luciferase transient expression assay with cultured Drosophila S2 cells and the lip4 promoter-luciferase fusion genes with and without mutations in the dNF-Y-binding consensuses showed that each of the three dNF-Y consensus sequences negatively regulated lip4 gene promoter activity. Consistent with these results, qRT-PCR analysis with the dNF-YA knockdown third instar larvae revealed that endogenous lip4 mRNA levels were increased by the knockdown of dNF-YA in vivo. The specific knockdown of dNF-YA in the fat body with the collagen-GAL4 driver resulted in smaller oil droplets in the fat body cells. Collectively, these results suggest that dNF-Y is involved in lipid storage through its negative regulation of lip4 gene transcription.

The animal nuclear factor Y: an enigmatic and important heterotrimeric transcription factor

Nuclear factor Y (NF-Y) is a heterotrimeric transcription factor with the ability to bind to CCAAT boxes in nearly all eukaryotes and has long been a topic of interest since it is first identified. In plants, due to each subunit of NF-Y is encoded by multiple gene families, there are a wide variety NF-Y complex combinations that fulfill many pivotal functions. However, the animal NF-Y complex usually has only one type of combination, as each subunit is generally encoded by a single gene. Even though, mounting evidence points to that the animal NF-Y complex is also essential for numerous biological processes involved in proliferation and apoptosis, cancer and tumor, stress responses, growth and development. Therefore, a relatively comprehensive functional dissection of animal NF-Y will enable a deeper comprehension of how lesser combinations of the NF-Y complex regulate diverse aspects of biology processes in animal. Here, we focus mainly on reviewing recent advances related to NF-Y in the animal field, including subunit structural characteristics, expression regulation models and biological functions, and we also discuss future directions.

NF-Y in invertebrates

Both Drosophila melanogaster and Caenorhabditis elegans (C. elegans) are useful model organisms to study in vivo roles of NF-Y during development. Drosophila NF-Y (dNF-Y) consists of three subunits dNF-YA, dNF-YB and dNF-YC. In some tissues, dNF-YC-related protein Mes4 may replace dNF-YC in dNF-Y complex. Studies with eye imaginal disc-specific dNF-Y-knockdown flies revealed that dNF-Y positively regulates the sevenless gene encoding a receptor tyrosine kinase, a component of the ERK pathway and negatively regulates the Sensless gene encoding a transcription factor to ensure proper development of R7 photoreceptor cells together with proper R7 axon targeting. dNF-Y also controls the Drosophila Bcl-2 (debcl) to regulate apoptosis. In thorax development, dNF-Y is necessary for both proper Drosophila JNK (basket) expression and JNK signaling activity that is responsible for thorax development. Drosophila p53 gene was also identified as one of the dNF-Y target genes in this system. C. elegans contains two forms of NF-YA subunit, CeNF-YA1 and CeNF-YA2. C. elegans NF-Y (CeNF-Y) therefore consists of CeNF-YB, CeNF-YC and either CeNF-YA1 or CeNF-YA2. CeNF-Y negatively regulates expression of the Hox gene egl-5 (ortholog of Drosophila Abdominal-B) that is involved in tail patterning. CeNF-Y also negatively regulates expression of the tbx-2 gene that is essential for development of the pharyngeal muscles, specification of neural cell fate and adaptation in olfactory neurons. Negative regulation of the expression of egl-5 and tbx-2 by CeNF-Y provides new insight into the physiological meaning of negative regulation of gene expression by NF-Y during development. In addition, studies on NF-Y in platyhelminths are also summarized. This article is part of a Special Issue entitled: Nuclear Factor Y in Development and Disease, edited by Prof. Roberto Mantovani.

Tetramethylpyrazine induces SH-SY5Y cell differentiation toward the neuronal phenotype through activation of the PI3K/Akt/Sp1/TopoIIβ pathway

Tetramethylpyrazine (TMP) is an active compound extracted from the traditional Chinese medicinal herb Chuanxiong. Previously, we have shown that TMP induces human SH-SY5Y neuroblastoma cell differentiation toward the neuronal phenotype by targeting topoisomeraseIIβ (TopoIIβ), a protein implicated in neural development. In the present study, we aimed to elucidate whether the transcriptional factors specificity protein 1 (Sp1) and nuclear factor Y (NF-Y), in addition to the upstream signaling pathways ERK1/2 and PI3K/Akt, are involved in modulating TopoIIβ expression in the neuronal differentiation process. We demonstrated that SH-SY5Y cells treated with TMP (80μM) terminally differentiated into neurons, characterized by increased neuronal markers, tubulin βIII and microtubule associated protein 2 (MAP2), and increased neurite outgrowth, with no negative effect on cell survival. TMP also increased the expression of TopoIIβ, which was accompanied by increased expression of Sp1 in the differentiated neuron-like cells, whereas NF-Y protein levels remained unchanged following the differentiation progression. We also found that the phosphorylation level of Akt, but not ERK1/2, was significantly increased as a result of TMP stimulation. Furthermore, as established by chromatin immunoprecipitation (ChIP) assay, activation of the PI3K/Akt pathway increased Sp1 binding to the promoter of the TopoIIβ gene. Blockage of PI3K/Akt was shown to lead to subsequent inhibition of TopoIIβ expression and neuronal differentiation. Collectively, the results indicate that the PI3K/Akt/Sp1/TopoIIβ signaling pathway is necessary for TMP-induced neuronal differentiation. Our findings offer mechanistic insights into understanding the upstream regulation of TopoIIβ in neuronal differentiation, and suggest potential applications of TMP both in neuroscience research and clinical practice to treat relevant diseases of the nervous system.

Digital gene expression approach over multiple RNA-Seq data sets to detect neoblast transcriptional changes in Schmidtea mediterranea

BACKGROUND

The freshwater planarian Schmidtea mediterranea is recognised as a valuable model for research into adult stem cells and regeneration. With the advent of the high-throughput sequencing technologies, it has become feasible to undertake detailed transcriptional analysis of its unique stem cell population, the neoblasts. Nonetheless, a reliable reference for this type of studies is still lacking.

RESULTS

Taking advantage of digital gene expression (DGE) sequencing technology we compare all the available transcriptomes for S. mediterranea and improve their annotation. These results are accessible via web for the community of researchers. Using the quantitative nature of DGE, we describe the transcriptional profile of neoblasts and present 42 new neoblast genes, including several cancer-related genes and transcription factors. Furthermore, we describe in detail the Smed-meis-like gene and the three Nuclear Factor Y subunits Smed-nf-YA, Smed-nf-YB-2 and Smed-nf-YC.

CONCLUSIONS

DGE is a valuable tool for gene discovery, quantification and annotation. The application of DGE in S. mediterranea confirms the planarian stem cells or neoblasts as a complex population of pluripotent and multipotent cells regulated by a mixture of transcription factors and cancer-related genes.

Nuclear transcription factor Y and its roles in cellular processes related to human disease

Nuclear transcription factor Y (NF-Y) is an example of a transcriptional regulation factor in eukaryotes consisting of three different subunits, NF-YA, NF-YB and NF-YC, which are all necessary for formation of NF-Y complexes and binding to CCAAT boxes in promoters of its target genes. Highly conserved between human and Drosophila, NF-Y regulates transcription of various genes related to the cell cycle and various human diseases. Drosophila models have been widely used as tools for studying genetics and developmental biology and more recently for analyzing the functions of human disease genes, including those responsible for developmental and neurological disorders, cancer, cardiovascular disease and metabolic and storage diseases, as well as genes required for function of the visual, auditory and immune systems. In this review, in vivo findings from Drosophila models relevant to the roles of NF-Y in various human diseases are summarized. Recent studies have demonstrated novel contributions of dNF-Y to apoptosis and apoptosis-induced proliferation, and in photoreceptor cell differentiation during the development of the Drosophila compound eye.

The NF-Y complex negatively regulates Caenorhabditis elegans tbx-2 expression

T-box genes are frequently expressed in dynamic patterns during animal development, but the mechanisms controlling expression of these genes are not well understood. The Caenorhabditis elegans T-box gene tbx-2 is essential for development of the ABa-derived pharyngeal muscles, specification of neural cell fate in the HSN/PHB lineage, and adaptation in olfactory neurons. The tbx-2 expression pattern is complex, and expression has been described in pharyngeal precursors and body wall muscles during embryogenesis, and amphid sensory neurons and pharyngeal neurons in adults. To examine mechanisms regulating tbx-2 gene expression, we performed an RNAi screen of transcription factor genes in strains containing a Ptbx-2::gfp reporter and identified the Nuclear Factor Y (NF-Y) complex as a negative regulator of tbx-2 expression. NF-Y is a heterotrimeric CCAAT-binding complex consisting of A-C subunits, and reduction of the NF-Y subunits nfya-1, nfyb-1, or nfyc-1 by RNAi or using mutants results in ectopic Ptbx-2::gfp expression in hypodermal seam cells and gut. Mutation of two CCAAT-boxes in the tbx-2 promoter results in a similar pattern of ectopic Ptbx-2::gfp expression, suggesting NF-Y directly represses the tbx-2 promoter. tbx-2 mRNA is moderately increased in nfya-1 null mutants, indicating NF-Y represses expression of endogenous tbx-2. Finally we identify and characterize a second-site mutation that enhances lethality of a temperature sensitive tbx-2 mutant and show that this mutation is a deletion in the nfyb-1 gene. Together, these results identify NF-Y as an important regulator of tbx-2 function in vivo.

Overexpression of ubiquitin carboxyl terminal hydrolase impairs multiple pathways during eye development in Drosophila melanogaster

UCH-L1 (ubiquitin carboxyl terminal hydrolase L1) is well known as an enzyme that hydrolyzes polyubiquitin at its C-terminal to release ubiquitin monomers. Although the overexpression of UCH-L1 inhibits proteasome activity in cultured cells, its biological significance in living organisms has not been clarified in detail. Here, we utilized Drosophila as a model system to examine the effects of the overexpression of dUCH, a Drosophila homologue of UCH-L1, on development. Overexpression in the eye imaginal discs induced a rough eye phenotype in the adult, at least partly resulting from the induction of caspase-dependent apoptosis followed by compensatory proliferation. Genetic crosses with enhancer trap lines marking the photoreceptor cells also revealed that the overexpression of dUCH specifically impaired R7 photoreceptor cell differentiation with a reduction in activated extracellular-signal-regulated kinase signals. Furthermore, the dUCH-induced rough eye phenotype was rescued by co-expression of the sevenless gene or the Draf gene, a downstream component of the mitogen-activated protein kinase (MAPK) cascade. These results indicate that the overexpression of dUCH impairs R7 photoreceptor cell differentiation by down-regulating the MAPK pathway. Interestingly, this process appears to be independent of its pro-apoptotic function.