MRG1 binds to the LIM domain of Lhx2 and may function as a coactivator to stimulate glycoprotein hormone alpha-subunit gene expression

Systematic identification of transcriptional activation domains from non-transcription factor proteins in plants and yeast

Transcription factors can promote gene expression through activation domains. Whole-genome screens have systematically mapped activation domains in transcription factors but not in non-transcription factor proteins (e.g., chromatin regulators and coactivators). To fill this knowledge gap, we employed the activation domain predictor PADDLE to analyze the proteomes of Arabidopsis thaliana and Saccharomyces cerevisiae. We screened 18,000 predicted activation domains from >800 non-transcription factor genes in both species, confirming that 89% of candidate proteins contain active fragments. Our work enables the annotation of hundreds of nuclear proteins as putative coactivators, many of which have never been ascribed any function in plants. Analysis of peptide sequence compositions reveals how the distribution of key amino acids dictates activity. Finally, we validated short, "universal" activation domains with comparable performance to state-of-the-art activation domains used for genome engineering. Our approach enables the genome-wide discovery and annotation of activation domains that can function across diverse eukaryotes.

Systematic identification of transcriptional activator domains from non-transcription factor proteins in plants and yeast

Transcription factors promote gene expression via trans-regulatory activation domains. Although whole genome scale screens in model organisms (e.g. human, yeast, fly) have helped identify activation domains from transcription factors, such screens have been less extensively used to explore the occurrence of activation domains in non-transcription factor proteins, such as transcriptional coactivators, chromatin regulators and some cytosolic proteins, leaving a blind spot on what role activation domains in these proteins could play in regulating transcription. We utilized the activation domain predictor PADDLE to mine the entire proteomes of two model eukaryotes, Arabidopsis thaliana and Saccharomyces cerevisiae ( 1 ). We characterized 18,000 fragments covering predicted activation domains from >800 non-transcription factor genes in both species, and experimentally validated that 89% of proteins contained fragments capable of activating transcription in yeast. Peptides with similar sequence composition show a broad range of activities, which is explained by the arrangement of key amino acids. We also annotated hundreds of nuclear proteins with activation domains as putative coactivators; many of which have never been ascribed any function in plants. Furthermore, our library contains >250 non-nuclear proteins containing peptides with activation domain function across both eukaryotic lineages, suggesting that there are unknown biological roles of these peptides beyond transcription. Finally, we identify and validate short, 'universal' eukaryotic activation domains that activate transcription in both yeast and plants with comparable or stronger performance to state-of-the-art activation domains. Overall, our dual host screen provides a blueprint on how to systematically discover novel genetic parts for synthetic biology that function across a wide diversity of eukaryotes.

Significance Statement

Activation domains promote transcription and play a critical role in regulating gene expression. Although the mapping of activation domains from transcription factors has been carried out in previous genome-wide screens, their occurrence in non-transcription factors has been less explored. We utilize an activation domain predictor to mine the entire proteomes of Arabidopsis thaliana and Saccharomyces cerevisiae for new activation domains on non-transcription factor proteins. We validate peptides derived from >750 non-transcription factor proteins capable of activating transcription, discovering many potentially new coactivators in plants. Importantly, we identify novel genetic parts that can function across both species, representing unique synthetic biology tools.

Pathophysiological Role of Variants of the Promoter Region of CITED2 Gene in Sporadic Tetralogy of Fallot Patients with Cellular Function Verification

Tetralogy of Fallot (TOF) is a common congenital heart malformation. Genetic variants in the CITED2 coding region are known to be significantly associated with cardiac malformation, but the role of variants in the CITED2 promoter region in the development of TOF remains unclear. In this study, we investigated CITED2 promoter variants in the DNA of 605 subjects, including 312 TOF patients and 293 unrelated healthy controls, by Sanger sequencing. We identified nine CITED2 gene promoter variants (including one novel heterozygous variant). Six were found only in patients with TOF and none in the control group. The transcriptional activity of the CITED2 gene promoter in mouse cardiomyocyte (HL-1) cells was significantly altered by the six variants (p < 0.05). The results of the electrophoretic mobility change assay and JASPAR database analysis showed that these variants generated or destroyed a series of possible transcription factor binding sites, resulting in changes in the CITED2 protein expression. We conclude that CITED2 promoter variants in TOF patients affect transcriptional activity and may be involved in the occurrence and progression of TOF. These findings may provide new insights into molecular pathogenesis and potential therapeutic insights in patients with TOF.

Cell fate decisions, transcription factors and signaling during early retinal development

The development of the vertebrate eyes is a complex process starting from anterior-posterior and dorso-ventral patterning of the anterior neural tube, resulting in the formation of the eye field. Symmetrical separation of the eye field at the anterior neural plate is followed by two symmetrical evaginations to generate a pair of optic vesicles. Next, reciprocal invagination of the optic vesicles with surface ectoderm-derived lens placodes generates double-layered optic cups. The inner and outer layers of the optic cups develop into the neural retina and retinal pigment epithelium (RPE), respectively. In vitro produced retinal tissues, called retinal organoids, are formed from human pluripotent stem cells, mimicking major steps of retinal differentiation in vivo. This review article summarizes recent progress in our understanding of early eye development, focusing on the formation the eye field, optic vesicles, and early optic cups. Recent single-cell transcriptomic studies are integrated with classical in vivo genetic and functional studies to uncover a range of cellular mechanisms underlying early eye development. The functions of signal transduction pathways and lineage-specific DNA-binding transcription factors are dissected to explain cell-specific regulatory mechanisms underlying cell fate determination during early eye development. The functions of homeodomain (HD) transcription factors Otx2, Pax6, Lhx2, Six3 and Six6, which are required for early eye development, are discussed in detail. Comprehensive understanding of the mechanisms of early eye development provides insight into the molecular and cellular basis of developmental ocular anomalies, such as optic cup coloboma. Lastly, modeling human development and inherited retinal diseases using stem cell-derived retinal organoids generates opportunities to discover novel therapies for retinal diseases.

Genetic Variants of CITED2 Gene Promoter in Human Atrial Septal Defects: Case-Control Study and Cellular Functional Verification

Atrial septal defect (ASD) is one of the most common forms of congenital heart disease (CHD). Genetic variants in the coding region of the CITED2 gene are known to be significantly correlated with CHD, but the role of variants in the promoter region of CITED2 is unknown. We investigated variants in the promoter of the CITED2 gene in 625 subjects (332 ASD and 293 healthy controls) through Sanger sequencing. Four variants in the CITED2 gene promoter were found only in eight ASD patients with zero occurrence in the control subjects (one case of g.4078A>C(rs1165649373), one case of g.4240C>A(rs1235857801), four cases of g.4935C>T(rs111470468), two cases of g.5027C>T(rs112831934)). Cellular functional analysis showed that these four variants significantly changed the transcriptional activity of the CITED2 gene promoter in HEK-293 and HL-1 cells. Electrophoretic mobility change assay results and JASPAR database analysis demonstrated that these variants created or destroyed a series of possible transcription factor binding sites, resulting in changes in the expression of CITED2 protein. We conclude that the variants of CITED2 promoter in ASD patients affect the transcriptional activity and are likely involved in the occurrence and development of ASD. These findings provide new perspectives on the pathogenesis and potential therapeutic insights of ASD.

Integrative Biological Network Analysis to Identify Shared Genes in Metabolic Disorders

Identification of common molecular mechanisms in interrelated diseases is essential for better prognoses and targeted therapies. However, complexity of metabolic pathways makes it difficult to discover common disease genes underlying metabolic disorders; and it requires more sophisticated bioinformatics models that combine different types of biological data and computational methods. Accordingly, we built an integrative network analysis model to identify shared disease genes in metabolic syndrome (MS), type 2 diabetes (T2D), and coronary artery disease (CAD). We constructed weighted gene co-expression networks by combining gene expression, protein-protein interaction, and gene ontology data from multiple sources. For 90 different configurations of disease networks, we detected the significant modules by using MCL, SPICi, and Linkcomm graph clustering algorithms. We also performed a comparative evaluation on disease modules to determine the best method providing the highest biological validity. By overlapping the disease modules, we identified 22 shared genes for MS-CAD and T2D-CAD. Moreover, 19 out of these genes were directly or indirectly associated with relevant diseases in the previous medical studies. This study does not only demonstrate the performance of different biological data sources and computational methods in disease-gene discovery, but also offers potential insights into common genetic mechanisms of the metabolic disorders.

Role of CITED2 in stem cells and cancer

Cbp/P300 interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) is a transcription co-factor that interacts with several other transcription factors and co-factors, and serves critical roles in fundamental cell processes, including proliferation, apoptosis, differentiation, migration and autophagy. The interacting transcription factors or co-factors of CITED2 include LIM homeobox 2, transcription factor AP-2, SMAD2/3, peroxisome proliferator-activated receptor γ, oestrogen receptor, MYC, Nucleolin and p300/CBP, which regulate downstream gene expression, and serve important roles in the aforementioned fundamental cell processes. Emerging evidence has demonstrated that CITED2 serves an essential role in embryonic and adult tissue stem cells, including hematopoietic stem cells and tendon-derived stem/progenitor cells. Additionally, CITED2 has been reported to function in different types of cancer. Although the functions of CITED2 in different tissues vary depending on the interaction partner, altered CITED2 expression or altered interactions with transcription factors or co-factors result in alterations of fundamental cell processes, and may affect stem cell maintenance or cancer cell survival. The aim of this review is to summarize the molecular mechanisms of CITED2 function and how it serves a role in stem cells and different types of cancer based on the currently available literature.

Aberrant expression of CITED2 promotes prostate cancer metastasis by activating the nucleolin-AKT pathway

Despite many efforts to develop hormone therapy and chemotherapy, no effective strategy to suppress prostate cancer metastasis has been established because the metastasis is not well understood. We here investigate a role of CBP/p300-interacting transactivator with E/D-rich carboxy-terminal domain-2 (CITED2) in prostate cancer metastasis. CITED2 is highly expressed in metastatic prostate cancer, and its expression is correlated with poor survival. The CITED2 gene is highly activated by ETS-related gene that is overexpressed due to chromosomal translocation. CITED2 acts as a molecular chaperone to guide PRMT5 and p300 to nucleolin, thereby activating nucleolin. Informatics and experimental data suggest that the CITED2-nucleolin axis is involved in prostate cancer metastasis. This axis stimulates cell migration through the epithelial-mesenchymal transition and promotes cancer metastasis in a xenograft mouse model. Our results suggest that CITED2 plays a metastasis-promoting role in prostate cancer and thus could be a target for preventing prostate cancer metastasis.

Down-regulation of CITED2 attenuates breast tumor growth, vessel formation and TGF-β-induced expression of VEGFA

While we previously demonstrated that CITED2 expression in primary breast tumor tissues is elevated relative to normal mammary epithelium and inversely correlated with patient survival, its functional impact on primary tumor development and progression remained unknown. To address this issue, we examined the effect of CITED2 silencing on the growth of human breast cancer cell lines MDA-MB-231 and MDA-MB-468 following orthotopic administration in vivo. Here, we show that CITED2 silencing significantly attenuated MDA-MB-231 primary tumor growth concordant with reduced tumor vascularization, while MDA-MB-468 primary tumor growth and tumor vascularization remained unaffected. Correspondingly, expression of VEGFA was significantly reduced in shCITED2-expressing MDA-MB-231, but not MDA-MB-468 tumors. Consistent with the observed pattern of vascularization and VEGFA expression, we found that TGF-β stimulation induced expression of VEGFA and enhanced CITED2 recruitment to the VEGFA promoter in MDA-MA-231 cells, while failing to induce VEGFA expression in MDA-MB-468 cells. Further supporting its involvement in TGF-β-induced expression of VEGFA, CITED2 silencing prevented TGF-β induction of VEGFA expression in MDA-MB-231 cells. Collectively, these data indicate that CITED2 regulates primary breast tumor growth, likely by influencing tumor vasculature via TGF-β-dependent regulation of VEGFA.

CITED2 Restrains Proinflammatory Macrophage Activation and Response

Macrophages are strategically distributed in mammalian tissues and play an essential role in priming the immune response. However, macrophages need to constantly strike a balance between activation and inhibition states to avoid a futile inflammatory reaction. Here, we identify the CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2) as a potent repressor of macrophage proinflammatory activation. Gain- and loss-of-function studies revealed that CITED2 is required for optimal peroxisome proliferator-activated receptor gamma (PPARγ) activation and attendant select anti-inflammatory gene expression in macrophages. More importantly, deficiency of CITED2 resulted in significant attenuation of rosiglitazone-induced PPARγ activity, PPARγ recruitment to target gene promoters, and anti-inflammatory target gene expression in macrophages. Interestingly, deficiency of Cited2 strikingly heightened proinflammatory gene expression through stabilization of hypoxia-inducible factor 1 alpha (HIF1α) protein in macrophages. Further, overexpression of Egln3 or inhibition of HIF1α in Cited2-deficient macrophages completely reversed elevated proinflammatory cytokine/chemokine gene expression. Importantly, mice bearing a myeloid cell-specific deletion of Cited2 were highly susceptible to endotoxin-induced sepsis symptomatology and mortality. Collectively, our observations identify CITED2 as a novel negative regulator of macrophage proinflammatory activation that protects the host from inflammatory insults.

CITED2 attenuates macrophage recruitment concordant with the downregulation of CCL20 in breast cancer cells

The transcriptional co-regulator Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain-2 (CITED2) may promote breast tumor growth; however, the mechanisms by which its effects are mediated remain to be fully elucidated. Tumor-associated macrophages serve an important function in tumor development and progression and are recruited by chemotactic factors produced by cells within the tumor microenvironment. The present study assessed the effects of CITED2 silencing on macrophage recruitment in two xenograft mouse models of human breast cancer, one in which tumor growth was sensitive to CITED2 silencing (MDA-MB-231) and one in which it was insensitive (MDA-MB-468). The present study identified that silencing CITED2 significantly attenuated macrophage infiltration in MDA-MB-231 but not MDA-MB-468 orthotopic tumors, concordant with its effect on tumor growth. Correspondingly, conditioned media obtained from CITED2-silenced MDA-MB-231 cells exhibited a significantly decreased ability to induce macrophage recruitment by Transwell migration assay, whereas the chemotactic effect of MDA-MB-468 conditioned media was unaffected. Examining the expression of macrophage chemoattractants within orthotopic tumors and tumor cell-conditioned media revealed a significant decrease in C-C motif chemokine ligand (CCL)20 mRNA and protein expression following CITED2-silencing in MDA-MB-231 cells, compared with that in cells transfected with scramble shRNA. However, mRNA and protein expression was unaffected by CITED2-silencing in MDA-MB-468 cells. Furthermore, chromatin immunoprecipitation analysis revealed that CITED2 was localized to the CCL20 promoter in MDA-MB-231 cells, suggesting that it serves a direct function in its regulation, which is consistent with the effect of CITED2 silencing on CCL20 expression. Lastly, neutralizing CCL20 in the conditioned media of MDA-MB-231 cells significantly inhibited macrophage recruitment. Collectively, these results suggest that CITED2 is involved in modulating macrophage recruitment, representing a novel mechanism through which it may influence tumor growth. This may be partly mediated by regulating tumor cell production of the chemokine CCL20.

CITED2 affects leukemic cell survival by interfering with p53 activation

CITED2 (CBP/p300-interacting-transactivator-with-an-ED-rich-tail 2) is a regulator of the acetyltransferase CBP/p300 and elevated CITED2 levels are shown in a number of acute myeloid leukemia (AML). To study the in vivo role of CITED2 in AML maintenance, AML cells were transduced with a lentiviral construct for RNAi-mediated knockdown of CITED2. Mice transplanted with CITED2-knockdown AML cells (n=4) had a significantly longer survival compared to mice transplanted with control AML cells (P<0.02). In vitro, the reduction of CITED2 resulted in increased p53-mediated apoptosis and CDKN1A expression, whereas BCL2 levels were reduced. The activation of p53 upon CITED2 knockdown is not a direct consequence of increased CBP/p300-activity towards p53, since no increased formation of CBP/p300/p53 complexes was demonstrated and inhibition of CBP/p300-activity could not rescue the phenotype of CITED2-deficient cells. Instead, loss of CITED2 had an inhibitory effect on the AKT-signaling pathway, which was indicated by decreased levels of phosphorylated AKT and altered expression of the AKT-pathway regulators PHLDA3 and SOX4. Notably, simultaneous upregulation of BCL2 or downregulation of the p53-target gene PHLDA3 rescued the apoptotic phenotype in CITED2-knockdown cells. Furthermore, knockdown of CITED2 led to a decreased interaction of p53 with its inhibitor MDM2, which results in increased amounts of total p53 protein. In summary, our data indicate that CITED2 functions in pathways regulating p53 activity and therefore represents an interesting target for AML therapy, since de novo AML cases are characterized by an inactivation of the p53 pathway or deregulation of apoptosis-related genes.

Cited2 Regulates Neocortical Layer II/III Generation and Somatosensory Callosal Projection Neuron Development and Connectivity

The neocortex contains hundreds to thousands of distinct subtypes of precisely connected neurons, allowing it to perform remarkably complex tasks of high-level cognition. Callosal projection neurons (CPN) connect the cerebral hemispheres via the corpus callosum, integrating cortical information and playing key roles in associative cognition. CPN are a strikingly diverse set of neuronal subpopulations, and development of this diversity requires precise control by a complex, interactive set of molecular effectors. We have found that the transcriptional coregulator Cited2 regulates and refines two stages of CPN development. Cited2 is expressed broadly by progenitors in the embryonic day 15.5 subventricular zone, during the peak of superficial layer CPN birth, with a progressive postmitotic refinement in expression, becoming restricted to CPN of the somatosensory cortex postnatally. We generated progenitor-stage and postmitotic forebrain-specific Cited2 conditional knock-out mice, using the Emx1-Cre and NEX-Cre mouse lines, respectively. We demonstrate that Cited2 functions in progenitors, but is not necessary postmitotically, to regulate both (1) broad generation of layer II/III CPN and (2) acquisition of precise area-specific molecular identity and axonal/dendritic connectivity of somatosensory CPN. This novel CPN subtype-specific and area-specific control from progenitor action of Cited2 adds yet another layer of complexity to the multistage developmental regulation of neocortical development.

SIGNIFICANCE STATEMENT

This study identifies Cited2 as a novel subtype-specific and area-specific control over development of distinct subpopulations within the broad population of callosal projection neurons (CPN), whose axons connect the two cerebral hemispheres via the corpus callosum (CC). Currently, how the remarkable diversity of CPN subtypes is specified, and how they differentiate to form highly precise and specific circuits, are largely unknown. We found that Cited2 functions within subventricular zone progenitors to both broadly regulate generation of superficial layer CPN throughout the neocortex, and to refine precise area-specific development and connectivity of somatosensory CPN. Gaining insight into molecular development and heterogeneity of CPN will advance understanding of both diverse functions of CPN and of the remarkable range of neurodevelopmental deficits correlated with CPN/CC development.

Ectopic expression of CITED2 prior to reprogramming, promotes and homogenises the conversion of somatic cells into induced pluripotent stem cells

Cited2 plays crucial roles in mouse embryonic stem cells self-renewal, the initiation of the somatic reprogramming process into induced pluripotent stem cells (iPSC) and the suppression of cell senescence. Here, we investigated the potential of CITED2 expression in combination with the Oct4, Sox2, Klf4 and c-Myc factors for reprogramming of primary mouse embryonic fibroblasts (MEF) at passage 2 and 4. The ectopic CITED2 expression in primary MEF prior to the onset of the reprogramming process, generated iPSC with less variability in the expression of endogenous pluripotency-related genes. In contrast, part of the MEF reprogrammed without ectopic expression of CITED2 at passage 4 originated partially reprogrammed iPSC or pre-iPSC. However, the overexpression of CITED2 in the pre-iPSC was insufficient to complete the reprogramming process into iPSC. These results indicated that ectopic CITED2 expression at the onset of the reprogramming process in combination with the reprogramming factors promotes a complete and homogeneous conversion of somatic cells into iPSC.

CITED2 Cooperates with ISL1 and Promotes Cardiac Differentiation of Mouse Embryonic Stem Cells

The transcriptional regulator CITED2 is essential for heart development. Here, we investigated the role of CITED2 in the specification of cardiac cell fate from mouse embryonic stem cells (ESC). The overexpression of CITED2 in undifferentiated ESC was sufficient to promote cardiac cell emergence upon differentiation. Conversely, the depletion of Cited2 at the onset of differentiation resulted in a decline of ESC ability to generate cardiac cells. Moreover, loss of Cited2 expression impairs the expression of early mesoderm markers and cardiogenic transcription factors (Isl1, Gata4, Tbx5). The cardiogenic defects in Cited2-depleted cells were rescued by treatment with recombinant CITED2 protein. We showed that Cited2 expression is enriched in cardiac progenitors either derived from ESC or mouse embryonic hearts. Finally, we demonstrated that CITED2 and ISL1 proteins interact physically and cooperate to promote ESC differentiation toward cardiomyocytes. Collectively, our results show that Cited2 plays a pivotal role in cardiac commitment of ESC.

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Overexpression of CITED2 in ESC promotes cardiogenesis upon differentiation

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Cited2 depletion reduces ESC ability to generate cardiac cells

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Cited2 expression is enriched in cardiac progenitors

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CITED2 and ISL1 cooperate to promote ESC differentiation toward cardiomyocytes

Gene Expression in Mouse Thyrotrope Adenoma: Transcription Elongation Factor Stimulates Proliferation

Thyrotrope hyperplasia and hypertrophy are common responses to primary hypothyroidism. To understand the genetic regulation of these processes, we studied gene expression changes in the pituitaries of Cga(-/-) mice, which are deficient in the common α-subunit of TSH, LH, and FSH. These mice have thyrotrope hypertrophy and hyperplasia and develop thyrotrope adenoma. We report that cell proliferation is increased, but the expression of most stem cell markers is unchanged. The α-subunit is required for secretion of the glycoprotein hormone β-subunits, and mutants exhibit elevated expression of many genes involved in the unfolded protein response, consistent with dilation and stress of the endoplasmic reticulum. Mutants have elevated expression of transcription factors that are important in thyrotrope function, such as Gata2 and Islet 1, and those that stimulate proliferation, including Nupr1, E2f1, and Etv5. We characterized the expression and function of a novel, overexpressed gene, transcription elongation factor A (SII)-like 5 (Tceal5). Stable expression of Tceal5 in a pituitary progenitor cell line is sufficient to increase cell proliferation. Thus, Tceal5 may act as a proto-oncogene. This study provides a rich resource for comparing pituitary transcriptomes and an analysis of gene expression networks.

CITED2 Modulates Breast Cancer Metastatic Ability through Effects on IKKα

Previously, we identified the transcriptional coactivator CITED2 as a potential facilitator of bone metastasis using a murine mammary cancer model. Extending these studies to human breast cancer, it was observed that CITED2 mRNA expression was significantly elevated in patient specimens of metastatic breast cancer relative to primary tumors, with highest levels in metastasis to bone relative to non-bone sites. To further evaluate CITED2 functions in breast cancer metastasis, CITED2 expression was stably reduced in the human breast cancer cell lines MDA-MB-231 and MDA-MB-468, which are metastatic in animal models. While CITED2 knockdown had no effect on cell proliferation, cell migration and invasion were significantly reduced, as was the establishment of metastasis following intracardiac administration in athymic nude mice. To explore the mechanism behind these effects, gene expression following CITED2 knockdown in MDA-MB-231 cells by cDNA microarray was performed. As confirmed at the mRNA and protein levels in both MDA-MB-231 and MDA-MB-468 cells, expression of the NF-κB regulator IKKα was significantly reduced, along with several NF-κB targets with known roles in metastasis (OPN, MMP9, uPA, SPARC, IL11, and IL1β). Furthermore, ChIP assay revealed recruitment of CITED2 to the promoter of IKKα, indicating a direct role in regulating its expression. Consistent with reduced IKKα expression, CITED2 knockdown inhibited both canonical and noncanonical NF-κB signaling. Finally, restoration of IKKα expression following CITED2 knockdown in MDA-MB-231 and MDA-MB-468 cells rescued their invasive ability. Collectively, these data demonstrate that CITED2 modulates metastatic ability in human breast cancer cells, at least in part, through the regulation of IKKα.

IMPLICATIONS

The current study highlights the role of CITED2 in facilitating breast cancer metastasis, partly via regulation of IKKα. Mol Cancer Res; 14(8); 730-9. ©2016 AACR.

Transcription of follicle-stimulating hormone subunit genes is modulated by porcine LIM homeobox transcription factors, LHX2 and LHX3

The LIM-homeobox transcription factors LHX2 and LHX3s (LHX3a and LHX3b) are thought to be involved in regulating the pituitary glycoprotein hormone subunit genes Cga and Fshβ. These two factors show considerable differences in their amino acid sequences for DNA binding and protein-protein interactions and in their vital function in pituitary development. Hence, we compared the DNA binding properties and transcriptional activities of Cga and Fshβ between LHX2 and LHX3s. A gel mobility shift assay for approximately 1.1 kb upstream of Cga and 2.0 kb upstream of Fshβ varied in binding profiles between LHX2 and LHX3s. DNase I footprinting revealed DNA binding sites in 8 regions of the Cga promoter for LHX2 and LHX3s with small differences in the binding range and strength. In the Fshβ promoter, 14 binding sites were identified for LHX2 and LHX3, respectively. There were alternative binding sites to either gene in addition to similar differences observed in the Cga promoter. The transcriptional activities of LHX2 and LHX3s according to a reporter assay showed cell-type dependent activity with repression in the pituitary gonadotrope lineage LβT2 cells and stimulation in Chinese hamster ovary lineage CHO cells. Reactivity of LHX2 and LHX3s was observed in all regions, and differences were observed in the 5'-upstream region of Fshβ. However, immunohistochemistry showed that LHX2 resides in a small number of gonadotropes in contrast to LHX3. Thus, LHX3 mainly controls Cga and Fshβ expression.

Cited2 protein level in cumulus cells is a biomarker for human embryo quality and pregnancy outcome in one in vitro fertilization cycle

OBJECTIVE

To determine whether the levels of CBP/p300 interacting transactivator with ED-rich tail 2 (Cited2) protein in cumulus cells (CCs) derived from patients undergoing IVF related to infertility factors, embryo quality, and clinical outcomes in one IVF cycle.

DESIGN

Retrospective analysis of human CCs.

SETTING

Public hospital and university.

PATIENT(S)

A total of 103 (conventional) IVF patients and 32 intracytoplasmic sperm injection patients.

INTERVENTION(S)

All CCs from each patient's oocytes were considered as one sample. The patients were divided into two groups according to whether the Cited2/β-actin levels in their CCs were above or below the mean level detected for all patients.

MAIN OUTCOME MEASURE(S)

Embryo quality and clinical outcomes of IVF patients.

RESULT(S)

The oocytes derived from the group of patients whose CCs showed lower Cited2 levels displayed higher fertilization, transferable embryo, and implantation rates. Moreover, the patients in this group were more likely to have a successful pregnancy outcome. Among different infertility factors, a total of 78.6% of patients with polycystic ovary syndrome had a higher Cited2 level in CCs. Additionally, patients with a lower basal FSH level belonged to the higher Cited2 levels group. The expression of two genes (phosphoenolpyruvate carboxykinase 1 [PCK1] and progesterone receptor [PR]) and the glucose content in CCs were also markedly increased in CCs derived from patients with higher Cited2 levels.

CONCLUSION(S)

The present findings imply that Cited2 level in CCs is associated with polycystic ovary syndrome, embryo quality, and pregnancy outcome of IVF patients.

Drosophila eye developmental defect caused by elevation of the activity of the LIM-homeodomain protein, Lmx1a, requires its association with the Co-activator Chip

The LIM-homeodomain (LIM-HD) family member Lmx1a has been successfully used to induce dopaminergic neurons from other cell types, thus showing significant implications in replacement therapies of Parkinson's disease, but the underlying mechanism remains elusive. In this study, we used Drosophila eye as a model system to investigate how forced expression of dLmx1a, the fly homolog of human Lmx1a, alters cell identify. We found that ectopic expression of dLmx1a suppresses the formation of Drosophila eye tissue and identified the LIM and HD as two essential domains. dLmx1a requires and physically binds to Chip, a well-known cofactor of LIM-HD proteins. Chip connects two dLmx1a proteins to form a functional tetrameric complex. In addition, we provide evidence showing that dLmx1a expression results in the suppression of two retina determination gene eyes absent (eya) and string (stg). Taken together, our findings identified Chip as a novel partner of dLmx1a to alter cell differentiation in Drosophila eye through repressing eya and stg expression, and provide an animal model for further understanding the molecular mechanism whereby Lmx1a determines cell fate.

FBXL5 modulates HIF-1α transcriptional activity by degradation of CITED2

CITED2 is a ubiquitously expressed nuclear protein exhibiting a high affinity for the cysteine-histidine-rich domain 1 (CH1) of the transcriptional co-activators CBP/p300. CITED2 is particularly efficient in the inhibition of the hypoxia-inducible factor-1α (HIF-1α) dependent transcription by competing with it for the interaction with the CH1 domain. Here we report a direct and specific interaction between CITED2 and the F-box and leucine rich repeat protein 5 (FBXL5), a substrate adaptor protein which is part of E3 ubiquitin ligase complexes mediating protein degradation by the proteasome. We demonstrated that depletion of FBXL5 by RNA interference led to an increase of CITED2 protein levels. Conversely, overexpression of FBXL5 caused the decrease of CITED2 protein levels in a proteasome-dependent manner, and impaired the interaction between CITED2 and the CH1 domain of p300 in living cells. In undifferentiated mouse embryonic stem cells, the overexpression of FBXL5 also reduced Cited2 protein levels. Finally, we evidenced that FBXL5 overexpression and the consequent degradation of CITED2 enabled the transcriptional activity of the N-terminal transactivation domain of HIF-1α. Collectively, our results highlighted a novel molecular interaction between CITED2 and FBXL5, which might regulate the steady state CITED2 protein levels and contribute to the modulation of gene expression by HIF-1α.

Globularity and language-readiness: generating new predictions by expanding the set of genes of interest

This study builds on the hypothesis put forth in Boeckx and Benítez-Burraco (2014), according to which the developmental changes expressed at the levels of brain morphology and neural connectivity that resulted in a more globular braincase in our species were crucial to understand the origins of our language-ready brain. Specifically, this paper explores the links between two well-known 'language-related' genes like FOXP2 and ROBO1 implicated in vocal learning and the initial set of genes of interest put forth in Boeckx and Benítez-Burraco (2014), with RUNX2 as focal point. Relying on the existing literature, we uncover potential molecular links that could be of interest to future experimental inquiries into the biological foundations of language and the testing of our initial hypothesis. Our discussion could also be relevant for clinical linguistics and for the interpretation of results from paleogenomics.

Lhx2 regulates bone remodeling in mice by modulating RANKL signaling in osteoclasts

The LIM homeobox 2 (Lhx2) transcription factor Lhx2 has a variety of functions, including neural induction, morphogenesis, and hematopoiesis. Here we show the involvement of Lhx2 in osteoclast differentiation. Lhx2 was strongly expressed in osteoclast precursor cells but its expression was significantly reduced during receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis. Overexpression of Lhx2 in bone marrow-derived monocyte/macrophage lineage cells (BMMs), which are osteoclast precursor cells, attenuated RANKL-induced osteoclast differentiation by inhibiting the induction of nuclear factor of activated T cells c1 (NFATc1). Interestingly, interaction of Lhx2 proteins with c-Fos attenuated the DNA-binding ability of c-Fos and thereby inhibited the transactivation of NFATc1. Furthermore, Lhx2 conditional knockout mice exhibited an osteoporotic bone phenotype, which was related with increased osteoclast formation in vivo. Taken together, our results suggest that Lhx2 acts as a negative regulator of osteoclast formation in vitro and in vivo. The anti-osteoclastogenic effect of Lhx2 may be useful for developing a therapeutic strategy for bone disease.

The shape of the human language-ready brain

Our core hypothesis is that the emergence of our species-specific language-ready brain ought to be understood in light of the developmental changes expressed at the levels of brain morphology and neural connectivity that occurred in our species after the split from Neanderthals–Denisovans and that gave us a more globular braincase configuration. In addition to changes at the cortical level, we hypothesize that the anatomical shift that led to globularity also entailed significant changes at the subcortical level. We claim that the functional consequences of such changes must also be taken into account to gain a fuller understanding of our linguistic capacity. Here we focus on the thalamus, which we argue is central to language and human cognition, as it modulates fronto-parietal activity. With this new neurobiological perspective in place, we examine its possible molecular basis. We construct a candidate gene set whose members are involved in the development and connectivity of the thalamus, in the evolution of the human head, and are known to give rise to language-associated cognitive disorders. We submit that the new gene candidate set opens up new windows into our understanding of the genetic basis of our linguistic capacity. Thus, our hypothesis aims at generating new testing grounds concerning core aspects of language ontogeny and phylogeny.

Cited2 is required for the maintenance of glycolytic metabolism in adult hematopoietic stem cells

Mammalian adult hematopoietic stem cells (HSCs) reside in the hypoxic bone marrow microenvironment and display a distinct metabolic phenotype compared with their progenitors. It has been proposed that HSCs generate energy mainly through anaerobic glycolysis in a pyruvate dehydrogenase kinase (Pdk)-dependent manner. Cited2 is an essential regulator for HSC quiescence, apoptosis, and function. Herein, we show that conditional deletion of Cited2 in murine HSCs results in elevated levels of reactive oxygen species, decreased cellular glutathione content, increased mitochondrial activity, and decreased glycolysis. At the molecular level, Cited2 deficiency significantly reduced the expression of genes involved in metabolism, such as Pdk2, Pdk4, and lactate dehydrogenases B and D (LDHB and LDHD). Cited2-deficient HSCs also exhibited increased Akt signaling, concomitant with elevated mTORC1 activity and phosphorylation of FoxOs. Further, inhibition of PI3/Akt, but not mTORC1, partially rescued the repression of Pdk4 caused by deletion of Cited2. Altogether, our results suggest that Cited2 is required for the maintenance of adult HSC glycolytic metabolism likely through regulating Pdk2, Pdk4, LDHB, LDHD, and Akt activity.

Cited2 in hematopoietic stem cell function

PURPOSE OF REVIEW

Transcription co-regulator Cited2 is essential for mouse development. Recent work has shown that Cited2 plays important roles in normal hematopoiesis in fetal liver and adult bone marrow. This review focuses on the function of Cited2 in the maintenance of hematopoietic stem cells (HSCs) and its potential role in the metabolic regulation of HSCs.

RECENT FINDINGS

Fetal liver cells from Cited2 null embryos give rise to reduced numbers of hematopoietic colonies and display significantly impaired hematopoietic reconstitution capacity. In adult mice, conditional deletion of Cited2 markedly reduces the number of HSCs and compromises hematopoietic reconstitution in mice receiving a transplant of Cited2 deficient bone marrow cells. Additional deletion of Ink4a/Arf or p53 in a Cited2-deficient background restores HSC functionality. Meanwhile, Cited2 deficient HSCs display loss of quiescence, which can be partially rescued by additional deletion of hypoxia inducible factor-1α.

SUMMARY

Cited2 is an essential regulator in fetal liver and adult hematopoiesis. Further studies into the function of Cited2 and the underlying mechanism in the metabolic regulation of HSCs will provide a better understanding of the connection between energy metabolism and HSC quiescence and self-renewal. Investigations of the pathologic role of Cited2 in leukemogenesis may yield useful information in developing effective therapeutic strategies.

A cell-autonomous role of Cited2 in controlling myocardial and coronary vascular development

AIMS

Myocardial development is dependent on concomitant growth of cardiomyocytes and a supporting vascular network. The coupling of myocardial and coronary vascular development is partly mediated by vascular endothelial growth factor (VEGFA) signalling and additional unknown mechanisms. We examined the cardiomyocyte specific role of the transcriptional co-activator Cited2 on myocardial microstructure and vessel growth, in relation to Vegfa expression.

METHODS AND RESULTS

A cardiomyocyte-specific knockout of mouse Cited2 (Cited2(Nkx)) was analysed using magnetic resonance imaging and histology. Ventricular septal defects and significant compact layer thinning (P < 0.02 at right ventricular apex, P < 0.009 at the left ventricular apex in Cited2(Nkx) vs. controls, n = 11 vs. n = 7, respectively) were found. This was associated with a significant decrease in the number of capillaries to larger vessels (ratio 1.56 ± 0.56 vs. 3.25 ± 1.63, P = 2.7 × 10(-6) Cited2(Nkx) vs. controls, n = 11 vs. n = 7, respectively) concomitant with a 1.5-fold reduction in Vegfa expression (P < 0.02, Cited2(Nkx) vs. controls, n = 12 vs. n = 12, respectively). CITED2 was subsequently found at the Vegfa promoter in mouse embryonic hearts using chromatin immunoprecipitation, and moreover found to stimulate human VEGFA promoter activity in cooperation with TFAP2 transcription factors in transient transfection assays. There was no change in the myocardial expression of the left-right patterning gene Pitx2c, a previously known target of CITED2.

CONCLUSIONS

This study delineates a novel cell-autonomous role of Cited2 in regulating VEGFA transcription and the development of myocardium and coronary vasculature in the mouse. We suggest that coupling of myocardial and coronary growth in the developing heart may occur in part through a Cited2→Vegfa pathway.

CITED2 modulates estrogen receptor transcriptional activity in breast cancer cells

Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) is a member of the CITED family of non-DNA binding transcriptional co-activators of the p300/CBP-mediated transcription complex. Previously, we identified CITED2 as being overexpressed in human breast tumors relative to normal mammary epithelium. Upon further investigation within the estrogen receptor (ER)-positive subset of these breast tumor samples, we found that CITED2 mRNA expression was elevated in those associated with poor survival. In light of this observation, we investigated the effect of elevated CITED2 levels on ER function. While ectopic overexpression of CITED2 in three ER-positive breast cancer cell lines (MCF-7, T47D, and CAMA-1) did not alter cell proliferation in complete media, growth was markedly enhanced in the absence of exogenous estrogen. Correspondingly, cells overexpressing CITED2 demonstrated reduced sensitivity to the growth inhibitory effects of the selective estrogen receptor modulator, 4-hydroxytamoxifen. Subsequent studies revealed that basal ER transcriptional activity was elevated in CITED2-overexpressing cells and was further increased upon the addition of estrogen. Similarly, basal and estrogen-induced expression of the ER-regulated genes trefoil factor 1 (TFF1) and progesterone receptor (PGR) was higher in cells overexpressing CITED2. Concordant with this observation, ChIP analysis revealed higher basal levels of CITED2 localized to the TFF-1 and PGR promoters in cells with ectopic overexpression of CITED2, and these levels were elevated further in response to estrogen stimulation. Taken together, these data indicate that CITED2 functions as a transcriptional co-activator of ER in breast cancer cells and that its increased expression in tumors may result in estrogen-independent ER activation, thereby reducing estrogen dependence and response to anti-estrogen therapy.

Indoxyl sulfate signals for rapid mRNA stabilization of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) and suppresses the expression of hypoxia-inducible genes in experimental CKD and uremia

Chronic hypoxia in the tubulointerstitium serves as a final common pathway in progressive renal disease. Circumstantial evidence suggests that hypoxia-inducible factor (HIF)-1 in the ischemic tubules may be functionally inhibited in a chronic kidney disease (CKD) milieu. In this study, we hypothesized that indoxyl sulfate (IS), a uremic toxin, impairs the cellular hypoxic response. In human kidney (HK-2) proximal tubular cells, IS reduced the hypoxic induction of HIF-1 target genes. This effect was not associated with quantitative changes in the HIF-1α protein, but with functional impairment of the HIF-1α C-terminal transactivation domain (CTAD). Among factors that impeded the recruitment of transcriptional coactivators to the HIF-1αCTAD, IS markedly up-regulated Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) through a mechanism of post-transcriptional mRNA stabilization involving the extracellular signal-regulated kinase (ERK) 1/2 pathway. In vivo, disproportionate expression of HIF target genes was demonstrated in several CKD models, which was offset by an oral adsorbent, AST-120. Furthermore, administration of indole reduced the induction of angiogenic, hypoxia-inducible genes in rats with experimental heart failure. Results of these studies reveal a novel role of IS in modulating the transcriptional response of HIF-1 and provide insight into molecular mechanisms underlying progressive nephropathies as well as cardiovascular complications.

Comparison of extravillous trophoblast cells derived from human embryonic stem cells and from first trimester human placentas

INTRODUCTION

Preeclampsia and other placental pathologies are characterized by a lack of spiral artery remodeling associated with insufficient invasion by extravillous trophoblast cells (EVT). Because trophoblast invasion occurs in early pregnancy when access to human placental tissue is limited, there is a need for model systems for the study of trophoblast differentiation and invasion. Human embryonic stem cells (hESC) treated with BMP4- differentiate to trophoblast, and express HLA-G, a marker of EVT. The goals of the present study were to further characterize the HLA-G(+) cells derived from BMP4-treated hESC, and determine their suitability as a model.

METHODS

HESC were treated with BMP4 under 4% or 20% oxygen and tested in Matrigel invasion chambers. Both BMP4-treated hESC and primary human placental cells were separated into HLA-G(+) and HLA-G(-)/TACSTD2(+) populations with immunomagnetic beads and expression profiles analyzed by microarray.

RESULTS

There was a 10-fold increase in invasion when hESC were BMP4-treated. There was also an independent, stimulatory effect of oxygen on this process. Invasive cells expressed trophoblast marker KRT7, and the majority were also HLA-G(+). Gene expression profiles revealed that HLA-G(+), BMP4-treated hESC were similar to, but distinct from, HLA-G(+) cells isolated from first trimester placentas. Whereas HLA-G(+) and HLA-G(-) cells from first trimester placentas had highly divergent gene expression profiles, HLA-G(+) and HLA-G(-) cells from BMP4-treated hESC had somewhat similar profiles, and both expressed genes characteristic of early trophoblast development.

CONCLUSIONS

We conclude that hESC treated with BMP4 provide a model for studying transition to the EVT lineage.

CITED2 functions as a molecular switch of cytokine-induced proliferation and quiescence

Transforming growth factor-α (TGF-α)-induced proliferation and transforming growth factor-β (TGF-β)-mediated quiescence are intricately balanced in normal lung-tissue homeostasis but are deregulated during neoplastic progression of lung cancer. Here, we show that Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2), a novel MYC-interacting transcriptional modulator, responds to TGF-α induction and TGF-β suppression to orchestrate cellular proliferation and quiescence, respectively. Upon TGF-α induction, CITED2 was induced by MYC and further modulated MYC-mediated transcription in a feed-forward manner. CITED2 recruited p300 to promote MYC-p300-mediated transactivation of E2F3, leading to increased G1/S cell cycle progression. Moreover, CITED2 inhibited cellular quiescence by enhancing MYC-mediated suppression of p21(CIP1). CITED2 interacted with histone deacetylase 1 (HDAC1) and potentiated MYC-HDAC1 complex formation. TGF-β stimulation provoked downregulation of CITED2, which abrogated MYC-HDAC1-mediated p21(CIP1) suppression, causing cellular quiescence. Ectopic CITED2 expression enhanced tumor growth in nude mice; furthermore, CITED2 knockdown caused tumor shrinkage and increased overall host mouse survival rates. Expression of CITED2/MYC/E2F3/p21(CIP1) signaling molecules was associated with poor prognosis of lung cancer patients. Thus, CITED2 functions as a molecular switch of TGF-α and TGF-β-induced growth control, and MYC-CITED2 signaling axis provides a new index for predicting clinical outcome.

The diverse biofunctions of LIM domain proteins: determined by subcellular localization and protein-protein interaction

The LIM domain is a cysteine- and histidine-rich motif that has been proposed to direct protein-protein interactions. A diverse group of proteins containing LIM domains have been identified, which display various functions including gene regulation and cell fate determination, tumour formation and cytoskeleton organization. LIM domain proteins are distributed in both the nucleus and the cytoplasm, and they exert their functions through interactions with various protein partners.

Molecular cloning of LIM homeodomain transcription factor Lhx2 as a transcription factor of porcine follicle-stimulating hormone beta subunit (FSHβ) gene

We cloned the LIM-homeodomain protein LHX2 as a transcription factor for the porcine follicle-stimulating hormone β subunit gene (Fshβ) by the Yeast One-Hybrid Cloning System using the upstream region of -852/-746 bases (b) from the transcription start site, called Fd2, as a bait sequence. The reporter assay in LβT2 and CHO cells revealed the presence of an LHX2-responsive region other than Fd2. A potential LHX2 binding sequence was confirmed as AATTAAT containing a consensus homeodomain binding core sequence AATT by Systematic Evolution of Ligands by Exponential Enrichment analysis. DNase I footprinting demonstrated three AATTAAT sequences located at regions -835/-829, -818/-812 and -806/-800 b in the Fd2 region and 12 binding sites in the distal and proximal regions mostly containing an AATT-core sequence. RT-PCR analysis of Lhx2 expression during porcine fetal and postnatal pituitary development showed a gradual increase from fetal day (f) 40 to postnatal day (p) 8 followed by a slight decrease to p230, suggesting that LHX2 may play its role largely in the late fetal and postnatal periods. The analyses of Lhx2 expression in pituitary tumor-derived cell lines showed their expressions in cell lines including αT31, LβT2 and others. Since LHX2 was previously identified as a transcription factor for Cga and the in vitro experiments in the present study suggested that LHX2 regulated the expression of Fshβ, it is possible that LHX2 controls the synthesis of FSH at the transcription level.

xCITED2 Induces Neural Genes in Animal Cap Explants of Xenopus Embryos

Neural tissue is arisen from presumptive ectoderm via inhibition of bone morphogenetic protein (BMP) signaling during Xenopus early development. Previous studies demonstrate that ectopic expression of dominant negative BMP4 receptor (DNBR) produces neural tissue in animal cap explants (AC) and also increases the expression level of various genes involved in neurogenesis. To investigate detail mechanism of neurogenesis in transcriptional level, we analyzed RNAs increased by DNBR using total RNA sequencing analysis and identified several candidate genes. Among them, xCITED2 (Xenopus CBP/p300-interacting transcription activator) was induced 4.6 fold by DNBR and preferentially expressed in neural tissues at tadpole stage. Ectopic expression of xCITED2 induced anterior neural genes without mesoderm induction and reduced BMP downstream genes, an eye specific marker and posterior neural marker. Taken together, these results suggest that xCITED2 may have a role in the differentiation of anterior neural tissue during Xenopus early development.

Pituitary transcription factors in the aetiology of combined pituitary hormone deficiency

The somatotropic axis is the central postnatal regulator of longitudinal growth. One of its major components--growth hormone--is produced by the anterior lobe of the pituitary, which also expresses and secretes five additional hormones (prolactin, thyroid stimulating hormone, follicle stimulating hormone, luteinizing hormone, adrenocorticotropic hormone). Proper development of the pituitary assures the regulation of critical processes such as metabolic control, puberty and reproduction, stress response and lactation. Ontogeny of the adenohypophysis is orchestrated by inputs from neighbouring tissues, cellular signalling molecules and transcription factors. Perturbation of expression or function of these factors has been implicated in the aetiology of combined pituitary hormone deficiency (CPHD). Mutations within the genes encoding for the transcription factors LHX3, LHX4, PROP1, and POU1F1 (PIT1) that act at different stages of pituitary development result in unique patterns of hormonal deficiencies reflecting their differential expression during organogenesis. In the case of LHX3 and LHX4 the phenotype may include extra-pituitary manifestations due to the function of these genes/proteins outside the pituitary gland. The remarkable variability in the clinical presentation of affected patients indicates the influence of the genetic background, environmental factors and possibly stochastic events. However, in the majority of CPHD cases the aetiology of this heterogeneous disease remains unexplained, which further suggests the involvement of additional genes. Identification of these factors might also help to close the gaps in our understanding of pituitary development, maintenance and function.

A novel role for transcription factor Lmo4 in thymus development through genetic interaction with Cited2

Deletion of the transcriptional modulator Cited2 in the mouse results in embryonic lethality, cardiovascular malformations, adrenal agenesis, cranial ganglia fusion, exencephaly, and left–right patterning defects, all seen with a varying degree of penetrance. The phenotypic heterogeneity, observed on different genetic backgrounds, indicates the existence of both genetic and environmental modifiers. Mice lacking the LIM domain-containing protein Lmo4 share specific phenotypes with Cited2 null embryos, such as embryonic lethality, cranial ganglia fusion, and exencephaly. These shared phenotypes suggested that Lmo4 may be a potential genetic modifier of the Cited2 phenotype. Examination of Lmo4-deficient embryos revealed partially penetrant cardiovascular malformations and hypoplastic thymus. Examination of Lmo4;Cited2 compound mutants indicated that there is a genetic interaction between Cited2 and Lmo4 in control of thymus development. Our data suggest that this may occur, in part, through control of expression of a common target gene, Tbx1, which is necessary for normal thymus development. Developmental Dynamics 239:1988–1994, 2010. © 2010 Wiley-Liss, Inc.

Regulation of LIM-domain-binding 1 protein expression by ubiquitination of Lys134

LDB1 (LIM-domain-binding 1) is a cofactor that participates in formation of transcriptional regulatory complexes involving transcription factors containing LIM domains as well as other factors. The amount of LDB1 protein in cells has previously been shown to be modulated by RNF12 (RING finger protein 12). RNF12 is an E3 ubiquitin ligase that can target LDB1 for poly-ubiquitination and degradation via the proteasome. We find that in HEK (human embryonic kidney)-293 cells expression of RNF12 leads to mono-ubiquitination of LDB1 and increased levels of LDB1 protein. Mutagenesis studies identified Lys134 of LDB1 as the residue that is mono-ubiquitinated by RNF12. Mutation of Lys134 of LDB1 to arginine blocks the formation of mono-ubiquitinated LDB1 and surprisingly also increases LDB1 protein expression in HEK-293 cells. This leads to a model in which Lys134 of LDB1 can be either mono-ubiquitinated, leading to stabilization, or poly-ubiquitinated, leading to degradation by the proteasome pathway. We also find that ubiquitin-LDB1 fusion proteins are stabilized in HEK-293 cells, offering further evidence that mono-ubiquitination stabilizes LDB1 in these cells. Expression in Xenopus laevis embryos of an LDB1 protein in which Lys134 is replaced with arginine leads to enhanced expression of the mutant protein as compared with the wild-type protein. These findings provide evidence that modification of Lys134 can play a major role in regulating LDB1 expression.

Cited2 is an essential regulator of adult hematopoietic stem cells

The regulatory pathways necessary for the maintenance of adult hematopoietic stem cells (HSCs) remain poorly defined. By using loss-of-function approaches, we report a selective and cell-autonomous requirement for the p300/CBP-binding transcriptional coactivator Cited2 in adult HSC maintenance. Conditional deletion of Cited2 in the adult mouse results in loss of HSCs causing multilineage bone marrow failure and increased lethality. In contrast, conditional ablation of Cited2 after lineage specification in lymphoid and myeloid lineages has no impact on the maintenance of these lineages. Additional deletion of Ink4a/Arf (encoding p16(Ink4a) and p19(Arf)) or Trp53 (encoding p53, a downstream target of p19(Arf)) in a Cited2-deficient background restores HSC functionality and rescues mice from bone marrow failure. Furthermore, we show that the critical role of Cited2 in primitive hematopoietic cells is conserved in humans. Taken together, our studies provide genetic evidence that Cited2 selectively maintains adult HSC functions, at least in part, via Ink4a/Arf and Trp53.

Transcription intermediary factor 1gamma decreases protein expression of the transcriptional cofactor, LIM-domain-binding 1

LIM-domain-binding 1 (LDB1) is a cofactor that participates in formation of regulatory complexes involving transcription factors containing LIM domains as well as other factors. We have examined the ability of transcriptional intermediary factor 1gamma (TIF1gamma) to decrease LDB1 expression. An expression vector for TIF1gamma was found to decrease expression of LDB1. A mutation which disrupts the ubiquitin ligase activity of TIF1gamma was found to block the ability of TIF1gamma to decrease LDB1 expression. Proteasome inhibitors were also able to block TIF1gamma effects on LDB1. Immunoprecipitation studies provided evidence that LDB1 interacts with TIF1gamma in intact cells. Knockdown of TIF1gamma in zebrafish embryos led to increased expression of LDB1 providing evidence for a physiological role of TIF1gamma in regulating LDB1 expression. Reporter gene assays demonstrated that TIF1gamma can alter the activity of LIM-homeodomain transcription factor-responsive promoters. These studies are consistent with a model in which TIF1gamma acts to ubiquitinate LDB1 leading to degradation of LDB1 and changes in transcription of LDB1-dependent promoters.

Functional characterization of two CITED3 homologs (gcCITED3a and gcCITED3b) in the hypoxia-tolerant grass carp, Ctenopharyngodon idellus

Background

CITED proteins belong to a family of non-DNA-binding transcriptional co-regulators that are characterized by a conserved ED-rich domain at the C-terminus. This family of genes is involved in the regulation of a variety of transcriptional responses through interactions with the CBP/p300 integrators and various transcription factors. In fish, very little is known about the expression and functions of CITEDs.

Results

We have characterized two closely related but distinct CITED3 genes, gcCited3a and gcCited3b, from the hypoxia-tolerant grass carp. The deduced gcCITED3a and gcCITED3b proteins share 72% amino acid identity, and are highly similar to the CITED3 proteins of both chicken and Xenopus. Northern blot analysis indicates that the mRNA expression of gcCited3a and gcCited3b is strongly induced by hypoxia in the kidney and liver, respectively. Luciferase reporter assays demonstrated that both gene promoters are activated by gcHIF-1. Further, ChIP assays comparing normal and hypoxic conditions reveal differential in vivo binding of gcHIF-1 to both gene promoters in kidney and liver tissues. HRE-luciferase reporter assays demonstrated that both gcCITED3a and gcCITED3b proteins inhibit gcHIF-1 transcriptional activity, and GST pull-down assays confirmed that both proteins bind specifically to the CH1 domain of the grass carp p300 protein.

Conclusion

The grass carp gcCITED3a and gcCITED3b genes are differentially expressed and regulated in different fish organs in response to hypoxic stress. This is the first report demonstrating in vivo regulation of two closely-related CITED3 isogenes by HIF-1, as well as CITED3 regulation of HIF-1 transcriptional activity in fish. Overall, our findings suggest that unique molecular mechanisms operate through these two gcCITED3 isoforms that likely play an important regulatory role in the hypoxic response in the grass carp.

Novel subtype-specific genes identify distinct subpopulations of callosal projection neurons

Little is known about the molecular development and heterogeneity of callosal projection neurons (CPN), cortical commissural neurons that connect homotopic regions of the two cerebral hemispheres via the corpus callosum and that are critical for bilateral integration of cortical information. Here we report on the identification of a series of genes that individually and in combination define CPN and novel CPN subpopulations during embryonic and postnatal development. We used in situ hybridization analysis, immunocytochemistry, and retrograde labeling to define the layer-specific and neuron-type-specific distribution of these newly identified CPN genes across different stages of maturation. We demonstrate that a subset of these genes (e.g., Hspb3 and Lpl) appear specific to all CPN (in layers II/III and V-VI), whereas others (e.g., Nectin-3, Plexin-D1, and Dkk3) discriminate between CPN of the deep layers and those of the upper layers. Furthermore, the data show that several genes finely subdivide CPN within individual layers and appear to label CPN subpopulations that have not been described previously using anatomical or morphological criteria. The genes identified here likely reflect the existence of distinct programs of gene expression governing the development, maturation, and function of the newly identified subpopulations of CPN. Together, these data define the first set of genes that identify and molecularly subcategorize distinct populations of callosal projection neurons, often located in distinct subdivisions of the canonical cortical laminae.

Conditional deletion of Cited2 results in defective corneal epithelial morphogenesis and maintenance

Cited2 is an important transcriptional cofactor involved in multiple organ development. Gene profile analysis has identified Cited2 as one of the transcription factors expressed at high levels in adult mouse cornea. To address the function of Cited2 in corneal morphogenesis, we deleted Cited2 in surface ectoderm derived ocular structures including cornea by crossing Cited2-floxed mice with Le-Cre transgenic mice. Cited2(flox/flox);Le-Cre(+) eyes invariably displayed corneal opacity and developed spontaneous corneal neovascularization at older age. Fewer layers of corneal epithelial cells and the absence of cytokeratin 12 (K12) expression featured Cited2 deficient postnatal and adult eyes. Cited2 deficient cornea exhibited impaired healing in response to corneal epithelial debridement by manifesting abnormal histology, lack of K12 expression and corneal neovascularization. Moreover, mechanistic studies suggest that Cited2 may play a role in corneal morphogenesis in part through modulating the expression of Pax6 and Klf4. Collectively, these findings demonstrate a novel function of Cited2 in postnatal corneal morphogenesis and maintenance. Our study will help better understand the molecular mechanisms involved in corneal biology, and more importantly, it may provide a valuable animal model for testing therapeutics in the treatment of corneal disorders, especially blindness as a result of corneal epithelial cell deficiency.

Discovery of transcriptional regulators and signaling pathways in the developing pituitary gland by bioinformatic and genomic approaches

We report a catalog of the mouse embryonic pituitary gland transcriptome consisting of five cDNA libraries including wild type tissue from E12.5 and E14.5, Prop1(df/df) mutant at E14.5, and two cDNA subtractions: E14.5 WT-E14.5 Prop1(df/df) and E14.5 WT-E12.5 WT. DNA sequence information is assembled into a searchable database with gene ontology terms representing 12,009 expressed genes. We validated coverage of the libraries by detecting most known homeobox gene transcription factor cDNAs. A total of 45 homeobox genes were detected as part of the pituitary transcriptome, representing most expected ones, which validated library coverage, and many novel ones, underscoring the utility of this resource as a discovery tool. We took a similar approach for signaling-pathway members with novel pituitary expression and found 157 genes related to the BMP, FGF, WNT, SHH and NOTCH pathways. These genes are exciting candidates for regulators of pituitary development and function.