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PubMed2026

MCM8 promotes colorectal cancer progression by competitively inhibiting HRD1-mediated CDC42 ubiquitination and degradation.

BACKGROUND: Colorectal cancer (CRC) ranks among the top three in both incidence and mortality rates of malignant tumors worldwide. For patients with advanced colon cancer, radical surgery is challenging, and chemotherapy drugs are prone to inducing drug resistance, resulting in a five-year survival rate of only 13.1%. Therefore, in-depth analysis of the occurrence, development, and drug resistance mechanisms of colon cancer is of great clinical significance for optimizing treatment strategies and improving patient prognosis. As one of the homologous recombination repair proteins, minichromosomal maintenance protein 8 (MCM8) not only participates in DNA replication initiation, homologous recombination repair, and genome stability maintenance in normal cells, but also has been reported to be abnormally highly expressed in multiple tumors (e.g. glioblastoma, cholangiocarcinoma, bladder cancer) to promote malignant progression. METHODS: This study focused on the expression and function of MCM8 in colon cancer. The expression level of MCM8 in colon cancer tissues and cells was detected, and its correlation with patients’ clinicopathological features and prognosis was analyzed. Combined with cell function experiments, protein-protein interaction verification assays, and in vivo tumorigenesis experiments, the effects of MCM8 on the biological behaviors of colon cancer cells and the underlying molecular mechanisms were explored. Meanwhile, rescue experiments were conducted to identify the key downstream molecules and pathways mediated by MCM8. Additionally, the relationship between MCM8 and chemoresistance of colon cancer cells was investigated. RESULTS: Our study indicated that MCM8 promotes the transition of the cell cycle from the G1 phase to the S phase in CRC cell lines(SW620, HCT116, CX-1). Moreover, our study showed that MCM8 interacted with Cdc42(Cell Division Cycle 42) and promoted its protein stability by competitively inhibiting the ubiquitination modification of Cdc42‘s E3 ubiquitin ligase HRD1(Hydroxymethylglutaryl Reductase Degradation Protein 1). The rescue experiment showed that MCM8 promoted the proliferation, cell cycle progression, invasion, tumor-forming ability in vivo and resistance to 5-FU of CRC cell lines (SW620FR, HCT15FR) through Cdc42, while inhibiting cell apoptosis. CONCLUSIONS: MCM8 is abnormally highly expressed in CRC and stabilizes Cdc42 protein by competitively inhibiting HRD1, thereby promoting the occurrence and development of CRC and the formation of 5-FU resistance.

Humans↗

PubMed2026

Increased IL4I1 expression predicts poor survival and modulates the immune microenvironment in acute myeloid leukemia.

BACKGROUND: The immunometabolic enzyme Interleukin-4-induced-1 (IL4I1) is implicated in cancer pathogenesis, yet its specific function and clinical relevance in acute myeloid leukemia (AML) remain unclear. METHODS: Comparative analysis of IL4I1 mRNA levels between AML patients and normal controls was performed using the Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases. The Kaplan–Meier survival analysis was conducted to evaluate the prognostic value of IL4I1. Functional insights were derived from analyses of differentially expressed genes (DEGs), Gene Set Enrichment Analysis (GSEA), and Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment. Immune infiltration was evaluated using the ssGSEA, ESTIMATE, quanTIseq and single-cell RNA sequencing (scRNA-seq) analysis. Finally, in vitro and in vivo functional experiments were perfromed to explore the impact of IL4I1 on AML progression and immunoregulation. RESULTS: IL4I1 expression was significantly elevated in AML compared to normal controls (p = 0.0004) and associated with poorer overall survival (p = 0.003). Bioinformatic analysis revealed that IL4I1 was linked to immune-related pathways—including humoral immune response, leukocyte interactions, and chemokine signaling—and to cellular amino acid metabolism. Its expression correlated with immune cell infiltration and checkpoint molecule expression. Experimentally, IL4I1 promoted leukemia cell proliferation in vitro and in vivo (p < 0.05). Furthermore, silencing IL4I1 suppressed M2 macrophage polarization and reduced secretion of inflammatory factors (p < 0.05). CONCLUSIONS: IL4I1 may serve as a potential biomarker for poor prognosis and an attractive target for immune-based therapeutic interventions in AML.

Humans↗

PubMed1995

The primate ovary contains a population of catecholaminergic neuron-like cells expressing nerve growth factor receptors.

The ovary of humans and nonhuman primates is innervated by sympathetic and sensory neurons of the peripheral nervous system. Recent studies demonstrated that the density of the sympathetic innervation to the rhesus monkey ovary is developmentally regulated, with adult density being attained around the time of puberty. In the present study, we used an immunocytochemical approach to obtain insights into the cell-cell signaling mechanisms that may contribute to the functional maintenance of this innervation. Because sympathetic neurons of the peripheral nervous system require target-derived neurotropins for their survival and function, experiments were conducted to determine if one of the receptors recognized by neurotropins is expressed in fibers innervating the primate ovary. A monoclonal antibody to the human low-affinity nerve growth factor (NGF) receptor, termed p75 NGFR because of its molecular weight, demonstrated the presence of this receptor in nerve fibers innervating the ovarian vasculature, interstitial tissue, and developing follicles of the gland. In addition, as shown in rodents, p75 NGFR immunoreactivity was detected in nonneuronal, endocrine cells of the ovary, specifically the thecal cell layer of developing follicles. Unexpectedly, however, the monkey ovary was also found to contain a network of small p75 NGFR immunoreactive cells distributed throughout the ovarian medulla and cortex. These cells, identified as such by confocal microscopy, had a neural-like appearance and displayed both neurofilament and neuron-specific enolase immunoreactivity. They appeared to be densely interconnected and were seen innervating the ovarian vasculature, the thecal cell layer of follicles, and, occasionally, primordial follicles. Double immunohistochemical procedures demonstrated that a subpopulation of these intraovarian, p75 NGFR-bearing neuron-like cells are catecholaminergic, as determined by their immunoreactivity to antibodies to tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis. RNA blot hybridization revealed the presence of p75 NGFR messenger RNA in the monkey ovary, thus demonstrating the ability of the gland to synthesize the receptors. These results demonstrate that the primate ovary contains an intrinsic network of neuron-like cells. Because such a neuronal network has not been detected in rodents or other non-primate species, it would appear that its presence in the primate ovary may have evolutionary significance.

Animals↗

PubMed2001

Inhibition of ERalpha-mediated trans-activation of human coagulation factor XII gene by heteromeric transcription factor NF-Y.

Human coagulation factor XII promoter contains an estrogen response element that mediates ligand-activated ERalpha induction of coagulation factor XII gene expression. The 3'-half of coagulation factor XII-estrogen response element overlaps a putative CCAAT box, the widespread regulatory element specifically recognized by the heteromeric transcription factor NF-Y. Transient cotransfection of NF-Y and ERalpha results in strong inhibition of estrogen stimulation of coagulation factor XII promoter activity. NF-Y antagonism is primarily exerted by the NF-YA subunit and does not require binding to the CCAAT element, as NF-YA mutants with impaired DNA binding capacity retain the ability to inhibit ERalpha trans-activation. EMSAs with increasing concentrations of recombinant NF-Y do not detect the formation of NF-Y-DNA complexes or show impairment of ERalpha binding to estrogen response element. Immunoprecipitation of whole cell extracts with anti-ERalpha antibody reveals an in vivo association between the two transcription factors, which is abolished by deletion of the NF-YA carboxyl-terminus. In functional experiments with sequential NF-YA deletion mutants the HAP2-homology region appears essential in eliciting NF-YA antagonistic activity. In conclusion, our results demonstrate that heteromeric transcription factor NF-Y inhibits estrogen induction of coagulation factor XII promoter in a DNA binding-independent fashion and suggest a novel role for NF-Y as a partner for the ERalpha transcription complex.

3T3 Cells↗

PubMed1999

Transition from monomeric to homodimeric DNA binding by nuclear receptors: identification of RevErbAalpha determinants required for RORalpha homodimer complex formation.

Nuclear hormone receptors belong to a class of transcription factors that recognize specific DNA sequences either as monomers, homodimers, or heterodimers with the common partner retinoic X receptor. In vitro mutagenesis studies, as well as determination of the crystal structure of several complexes formed by the DNA-binding domain of receptors bound to their cognate response elements, have begun to explain the molecular basis for protein-DNA and protein-protein interactions essential for high-affinity and specific DNA binding by nuclear receptors. In this study, we have used the related orphan nuclear receptors, RORalpha and RevErbAalpha, to study the molecular determinants involved in the transition from monomeric to homodimeric modes of DNA binding by nuclear receptors. While both receptors bind DNA as monomers to a response element containing a core AGGTCA half-site preceded by a 5'-A/T-rich flanking sequence, RevErbAalpha also binds as a homodimer to an extended DR2 element. Gain-of-function experiments using point mutations and subdomain swaps between RORalpha and RevErbAalpha identify four amino acids within RevErbAalpha sufficient to confer RORalpha with the ability to form cooperative homodimer complexes on an extended DR2. This study reveals how the transition from monomer to homodimer DNA binding by members of the nuclear receptor superfamily could be achieved from relatively few amino acid substitutions.

Amino Acid Sequence↗

PubMed2003

Predictors and clinical impact of epilepsy after subarachnoid hemorrhage.

OBJECTIVE: To determine the frequency, predictors, and impact on outcome of epilepsy developing during the first year after subarachnoid hemorrhage (SAH). METHODS: The authors prospectively analyzed 247 of 431 patients with SAH treated over a period of 5 years who were alive with follow-up at 12 months. Epilepsy was defined as two or more unprovoked seizures after hospital discharge. RESULTS: New-onset epilepsy occurred in 7% (n = 17) of patients; an additional 4% (n = 10) had only one seizure after discharge. Independent predictors of epilepsy included subdural hematoma (OR 9.9, 95% CI 1.9 to 52.8) and cerebral infarction (OR 3.9, 95% CI 1.4 to 11.3). Unlike those without seizures, patients who developed epilepsy failed to experience functional recovery on the modified Rankin Scale (mRS) between 3 and 12 months after SAH. At 12 months epilepsy was independently associated with severe disability (score >/= 3) on the mRS (OR 10.3, 95% CI 2.5 to 42.0), increased instrumental disability on the Lawton Instrumental Activities of Daily Living scale (OR 4.9; 95% CI 1.1 to 22.2), reduced quality of life on the Sickness Impact Profile (OR 4.5; 95% CI 1.1 to 18.0), and increased state anxiety on the Spielberger Anxiety Inventory (OR 4.8; 95% CI 1.1 to 20.4). Epilepsy was not associated with cognitive impairment, depression, or subjective life satisfaction. CONCLUSION: Epilepsy occurred in 7% of patients with SAH, was predicted by subdural hematoma and cerebral infarction, and was associated with poor functional recovery and quality of life. Our findings indicate that focal pathology, rather than diffuse injury from hemorrhage, is the principal cause of epilepsy after SAH.

Activities of Daily Living↗

PubMed2003

Localized JAK/STAT signaling is required for oriented cell rearrangement in a tubular epithelium.

Rearrangement of cells constrained within an epithelium is a key process that contributes to tubular morphogenesis. We show that activation in a gradient of the highly conserved JAK/STAT pathway is essential for orienting the cell rearrangement that drives elongation of a genetically tractable model. Using loss-of-function and gain-of-function experiments, we show that the components of the pathway from ligand to the activated transcriptional regulator STAT are required for cell rearrangement in the Drosophila embryonic hindgut. The difference in effect between localized expression of ligand (Unpaired) and dominant active JAK (Hopscotch) demonstrates that the ligand plays a cell non-autonomous role in hindgut cell rearrangement. Taken together with the appearance of STAT92E in a gradient in the hindgut epithelium, these results support a model in which an anteroposterior gradient of ligand results in a gradient of activated STAT. These results provide the first example in which JAK/STAT signaling plays a required role in orienting cell rearrangement that elongates an epithelium.

Animals↗

PubMed2003

Xenopus Cyr61 regulates gastrulation movements and modulates Wnt signalling.

Cyr61 is a secreted, heparin-binding, extracellular matrix-associated protein whose activities include the promotion of adhesion and chemotaxis, and the stimulation of fibroblast and endothelial cell growth. Many, if not all, of these activities of Cyr61 are mediated through interactions with integrins. We explore the role of Cyr61 in the early development of Xenopus laevis. Gain- and loss-of-function experiments show that Xcyr61 is required for normal gastrulation movements. This role is mediated in part through the adhesive properties of Xcyr61 and its related ability to modulate assembly of the extracellular matrix. In addition, Xcyr61 can, in a context-dependent manner, stimulate or inhibit signalling through the Wnt pathway. These properties of Xcyr61 provide a mechanism for integrating cell signalling, cell adhesion and cell migration during gastrulation.

Amino Acid Sequence↗

PubMed2003

Fusicoccin signaling reveals 14-3-3 protein function as a novel step in left-right patterning during amphibian embryogenesis.

To gain insight into the molecular mechanisms underlying the control of morphogenetic signals by H+ flux during embryogenesis, we tested Fusicoccin-A (FC), a compound produced by the fungus Fusicoccum amygdali Del. In plant cells, FC complexes with 14-3-3 proteins to activate H+ pumping across the plasma membrane. It has long been thought that FC acts on higher plants only; here, we show that exposing frog embryos to FC during early development specifically results in randomization of the asymmetry of the left-right (LR) axis (heterotaxia). Biochemical and molecular-genetic evidence is presented that 14-3-3-family proteins are an obligate component of Xenopus FC receptors and that perturbation of 14-3-3 protein function results in heterotaxia. The subcellular localization of 14-3-3 mRNAs and proteins reveals novel cytoplasmic destinations, and a left-right asymmetry at the first cell division. Using gain-of-function and loss-of-function experiments, we show that 14-3-3E protein is likely to be an endogenous and extremely early aspect of LR patterning. These data highlight a striking conservation of signaling pathways across kingdoms, suggest common mechanisms of polarity establishment between C. elegans and vertebrate embryos, and uncover a novel entry point into the pathway of left-right asymmetry determination.

14-3-3 Proteins↗

PubMed2003

Regulation of Msx genes by a Bmp gradient is essential for neural crest specification.

There is evidence in Xenopus and zebrafish embryos that the neural crest/neural folds are specified at the border of the neural plate by a precise threshold concentration of a Bmp gradient. In order to understand the molecular mechanism by which a gradient of Bmp is able to specify the neural crest, we analyzed how the expression of Bmp targets, the Msx genes, is regulated and the role that Msx genes has in neural crest specification. As Msx genes are directly downstream of Bmp, we analyzed Msx gene expression after experimental modification in the level of Bmp activity by grafting a bead soaked with noggin into Xenopus embryos, by expressing in the ectoderm a dominant-negative Bmp4 or Bmp receptor in Xenopus and zebrafish embryos, and also through Bmp pathway component mutants in the zebrafish. All the results show that a reduction in the level of Bmp activity leads to an increase in the expression of Msx genes in the neural plate border. Interestingly, by reaching different levels of Bmp activity in animal cap ectoderm, we show that a specific concentration of Bmp induces msx1 expression to a level similar to that required to induce neural crest. Our results indicate that an intermediate level of Bmp activity specifies the expression of Msx genes in the neural fold region. In addition, we have analyzed the role that msx1 plays on neural crest specification. As msx1 has a role in dorsoventral pattering, we have carried out conditional gain- and loss-of-function experiments using different msx1 constructs fused to a glucocorticoid receptor element to avoid an early effect of this factor. We show that msx1 expression is able to induce all other early neural crest markers tested (snail, slug, foxd3) at the time of neural crest specification. Furthermore, the expression of a dominant negative of Msx genes leads to the inhibition of all the neural crest markers analyzed. It has been previously shown that snail is one of the earliest genes acting in the neural crest genetic cascade. In order to study the hierarchical relationship between msx1 and snail/slug we performed several rescue experiments using dominant negatives for these genes. The rescuing activity by snail and slug on neural crest development of the msx1 dominant negative, together with the inability of msx1 to rescue the dominant negatives of slug and snail strongly argue that msx1 is upstream of snail and slug in the genetic cascade that specifies the neural crest in the ectoderm. We propose a model where a gradient of Bmp activity specifies the expression of Msx genes in the neural folds, and that this expression is essential for the early specification of the neural crest.

Animals↗

PubMed2004

Two zebrafish Notch-dependent hairy/Enhancer-of-split-related genes, her6 and her4, are required to maintain the coordination of cyclic gene expression in the presomitic mesoderm.

Alterations of the Delta/Notch signalling pathway cause multiple morphogenetic abnormalities in somitogenesis, including defects in intersomitic boundary formation and failure in maintenance of somite regularity. Notch signalling has been implicated in establishing the anteroposterior polarity within maturing somites and in regulating the activity of a molecular segmentation clock operating in the presomitic mesoderm. The pleiotropy of Notch signalling obscures the roles of this pathway in different steps of somitogenesis. One possibility is that distinct Notch effectors mediate different aspects of Notch signalling. In this study, we focus on two zebrafish Notch-dependent hairy/Enhancer-of-split-related transcription factors, Her6 and Her4, which are expressed at the transition zone between presomitic mesoderm and the segmented somites. The results of overexpression/gain-of-function and of morpholino-mediated loss-of-function experiments show that Her6 and Her4 are Notch signalling effectors that feedback on the clock and take part in the maintenance of cyclic gene expression coordination among adjacent cells in the presomitic mesoderm.

Animals↗

PubMed2004

The development of semicircular canals in the inner ear: role of FGFs in sensory cristae.

In the vertebrate inner ear, the ability to detect angular head movements lies in the three semicircular canals and their sensory tissues, the cristae. The molecular mechanisms underlying the formation of the three canals are largely unknown. Malformations of this vestibular apparatus found in zebrafish and mice usually involve both canals and cristae. Although there are examples of mutants with only defective canals, few mutants have normal canals without some prior sensory tissue specification, suggesting that the sensory tissues, cristae, might induce the formation of their non-sensory components, the semicircular canals. We fate-mapped the vertical canal pouch in chicken that gives rise to the anterior and posterior canals, using a fluorescent, lipophilic dye (DiI), and identified a canal genesis zone adjacent to each prospective crista that corresponds to the Bone morphogenetic protein 2 (Bmp2)-positive domain in the canal pouch. Using retroviruses or beads to increase Fibroblast Growth Factors (FGFs) for gain-of-function and beads soaked with the FGF inhibitor SU5402 for loss-of-function experiments, we show that FGFs in the crista promote canal development by upregulating Bmp2. We postulate that FGFs in the cristae induce a canal genesis zone by inducing/upregulating Bmp2 expression. Ectopic FGF treatments convert some of the cells in the canal pouch from the prospective common crus to a canal-like fate. Thus, we provide the first molecular evidence whereby sensory organs direct the development of the associated non-sensory components, the semicircular canals, in vertebrate inner ears.

Animals↗

PubMed2004

Zebrafish Dapper1 and Dapper2 play distinct roles in Wnt-mediated developmental processes.

Wnt signaling pathways in vertebrates use the phosphoprotein Dishevelled (Dvl). The cellular responses to Wnt signaling may in part be modulated by Dvl-associated proteins, including Dapper (Dpr). We have cloned and characterized the zebrafish Dpr paralogs Dpr1 and Dpr2. Loss-of-function studies reveal that endogenous Dpr1 but not Dpr2 is required to enhance Wnt/beta-catenin activity in zebrafish embryos that are hypomorphic for Wnt8. Conversely, Dpr2 but not Dpr1 is required for normal convergence extension movements in embryos that are hypomorphic for Stbm or Wnt11, supporting a functional interaction of Dpr2 with Wnt/Ca2+-PCP signaling. In gain-of-function experiments, Dpr1 but not Dpr2 induces Wnt/beta-catenin target genes. Dpr1 synergizes with zebrafish Dvl2, and with the Dvl-interacting kinases CK1epsilon, Par1 and CK2, in activating target genes. We conclude that two Dvl-associated paralogs, Dpr1 and Dpr2, participate in distinct Wnt-dependent developmental processes.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Transcriptional control of early tract formation in the embryonic chick midbrain.

The earliest step in establishing the complex neuronal networks in the vertebrate brain is the formation of a scaffold of axon tracts. How the formation of the early axon scaffold is controlled at the molecular level is unclear. Forming part of the scaffold, neurons located at the ventral midbrain-forebrain border (MFB) give rise to the medial longitudinal fascicle (mlf) and the posterior commissure (pc). We demonstrate that the homeobox genes Sax1, Six3, Emx2 and Pax6 are expressed in distinct domains in this area, suggesting that the specification of mlf and pc neurons might be controlled by the combinatorial activity of these transcription factors. We have tested this hypothesis by analysing the function of Sax1 in the embryonic chick brain. Gain-of-function experiments with Sax1 result in alterations to the early axon scaffold, most prominently an enlargement of the mlf at the expense of the pc. Ectopic expression of Sax1 also affects the expression of other ventral homeobox genes, particularly Six3 and Emx2. Our results indicate that the specification of neurons forming the early axon scaffold is governed by a homeobox code, thus resembling the mechanism of neuronal specification in the spinal cord.

Animals↗

PubMed2005

Essential role of non-canonical Wnt signalling in neural crest migration.

Migration of neural crest cells is an elaborate process that requires the delamination of cells from an epithelium and cell movement into an extracellular matrix. In this work, it is shown for the first time that the non-canonical Wnt signalling [planar cell polarity (PCP) or Wnt-Ca2+] pathway controls migration of neural crest cells. By using specific Dsh mutants, we show that the canonical Wnt signalling pathway is needed for neural crest induction, while the non-canonical Wnt pathway is required for neural crest migration. Grafts of neural crest tissue expressing non-canonical Dsh mutants, as well as neural crest cultured in vitro, indicate that the PCP pathway works in a cell-autonomous manner to control neural crest migration. Expression analysis of non-canonical Wnt ligands and their putative receptors show that Wnt11 is expressed in tissue adjacent to neural crest cells expressing the Wnt receptor Frizzled7 (Fz7). Furthermore, loss- and gain-of-function experiments reveal that Wnt11 plays an essential role in neural crest migration. Inhibition of neural crest migration by blocking Wnt11 activity can be rescued by intracellular activation of the non-canonical Wnt pathway. When Wnt11 is expressed opposite its normal site of expression, neural crest migration is blocked. Finally, time-lapse analysis of cell movement and cell protrusion in neural crest cultured in vitro shows that the PCP or Wnt-Ca2+ pathway directs the formation of lamellipodia and filopodia in the neural crest cells that are required for their delamination and/or migration.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Tsukushi controls ectodermal patterning and neural crest specification in Xenopus by direct regulation of BMP4 and X-delta-1 activity.

In Xenopus, ectodermal patterning depends on a mediolateral gradient of BMP signaling, higher in the epidermis and lower in the neuroectoderm. Neural crest cells are specified at the border between the neural plate and the epidermis, at intermediate levels of BMP signaling. We recently described a novel secreted protein, Tsukushi (TSK), which works as a BMP antagonist during chick gastrulation. Here, we report on the Xenopus TSK gene (X-TSK), and show that it is involved in neural crest specification. X-TSK expression accumulates after gastrulation at the anterior-lateral edges of the neural plate, including the presumptive neural crest region. In gain-of-function experiments, X-TSK can strongly enhance neural crest specification by the dorsolateral mesoderm or X-Wnt8 in ectodermal explants, while the electroporation of X-TSK mRNA in the lateral ectoderm of embryos after gastrulation can induce the expression of neural crest markers in vivo. By contrast, depletion of X-TSK in explants or embryos impairs neural crest specification. Similarly to its chick homolog, X-TSK works as a BMP antagonist by direct binding to BMP4. However, X-TSK can also indirectly regulate BMP4 mRNA expression at the neural plate border via modulation of the Delta-Notch signaling pathway. We show that X-TSK directly binds to the extracellular region of X-delta-1, and modulates Delta-dependent Notch activity. We propose that X-TSK plays a key role in neural crest formation by directly regulating BMP and Delta activities at the boundary between the neural and the non-neural ectoderm.

Animals↗

PubMed2006

NUBBIN and JAGGED define stamen and carpel shape in Arabidopsis.

Differential growth of tissues during lateral organ development is essential for producing variation in shape and size. Previous studies have identified JAGGED (JAG), a gene that encodes a putative C2H2 zinc-finger transcription factor, as a key regulator of shape that promotes growth in lateral organs. Although JAG expression is detected in all floral organs, loss-of-function jag alleles have their strongest effects on sepal and petal development, suggesting that JAG may act redundantly with other factors in stamens and carpels. Here, we show that NUBBIN (NUB), a gene closely related to JAG, is responsible for this redundancy. Unlike JAG, NUB is exclusively expressed in leaves, stamens and carpels, and briefly in petal primordia. Furthermore, whereas JAG expression extends into all cell layers of lateral organs, NUB is restricted to the interior adaxial side. Our analysis focuses on stamen and gynoecium development, where we find that NUB acts redundantly with JAG to promote the growth of the pollen-bearing microsporangia of the anthers and the carpel walls of the gynoecium, which enclose the ovules. JAG and NUB also act redundantly to promote the differentiation of adaxial cell types in the carpel walls, and in the establishment of the correct number of cell layers. The important role these two factors play in regulating organ growth is further demonstrated by gain-of-function experiments showing that ectopic NUB expression is sufficient to drive the proliferation of tissues and the amplification of cell-layer number.

Alleles↗

PubMed2006

Ci-FoxA-a is the earliest zygotic determinant of the ascidian anterior ectoderm and directly activates Ci-sFRP1/5.

This work focuses on the anteroposterior patterning of the ectoderm in the invertebrate chordate Ciona intestinalis. Previous work indicated that, by the eight-cell stage, the anterior and posterior animal blastomeres have acquired different properties, including a differential responsiveness to inducing signals from the underlying mesendoderm. Here, we investigated the molecular basis of this distinction. For this, we studied the regulation of the earliest marker specific for the anterior ectoderm, Ci-sFRP1/5, which is activated at the 64-cell stage. We first found that the activation of this marker in the anterior ectoderm does not involve communication with other lineages. We then identified, by phylogenetic footprinting and deletion analysis, a short conserved minimal enhancer driving the onset of expression of Ci-sFRP1/5. We showed that this enhancer was a direct target of the Ci-FoxA-a gene, a FoxA/HNF3 orthologue expressed in anterior ectodermal and mesendodermal lineages from the eight-cell stage. Gain- and loss-of-function experiments revealed that Ci-FoxA-a is necessary and sufficient within the ectoderm to impose an ectodermal anterior identity, and to repress the posterior programme. Thus, Ci-FoxA-a constitutes a major early zygotic anterior determinant for the ascidian ectoderm, acting autonomously in this territory, prior to the onset of vegetal inductions. Interestingly, while vertebrate FoxA2 are also involved in the regionalization of the ectoderm, they are thought to act during gastrulation to control, in the mesendoderm, the expression of organizer signals. We discuss the evolution of chordate ectodermal patterning in light of our findings.

Animals↗