Ectopic Expression of the Arabidopsis Transcriptional Activator Athb-1 Alters Leaf Cell Fate in Tobacco

Leaves of higher plants are produced in a sequential manner through the differentiation of cells that are derived from the shoot apical meristem. Current evidence suggests that this transition from meristematic to leaf cell fate requires the down-regulation of knotted1-like homeobox (knox) gene expression. If knox gene expression is not repressed, overall leaf shape and cellular differentiation within the leaf are perturbed. In order to identify genes that are required for the aquisition of leaf cell fates, we have genetically screened for recessive mutations that confer phenotypes similar to dominant mutations (e.g. Knotted1 and Rough sheath1) that result in the ectopic expression of class I knox genes. Independently derived mutations at the rough sheath2 (rs2) locus condition a range of pleiotropic leaf, node and internode phenotypes that are sensitive to genetic background and environment. Phenotypes include dwarfism, leaf twisting, disorganized differentiation of the blade-sheath boundary, aberrant vascular patterning and the generation of semi-bladeless leaves. knox genes are initially repressed in rs2 mutants as leaf founder cells are recruited in the meristem. However, this repression is often incomplete and is not maintained as the leaf progresses through developement. Expression studies indicate that three knox genes are ectopically or over-expressed in developing primordia and in mature leaves. We therefore propose that the rs2 gene product acts to repress knox gene expression (either directly or indirectly) and that rs2 gene action is essential for the elaboration of normal leaf morphology.

Download Full-text

fringeandNotchspecify polar cell fate duringDrosophilaoogenesis

Development ◽

10.1242/dev.128.12.2243 ◽

2001 ◽

Vol 128 (12) ◽

pp. 2243-2253 ◽

Cited By ~ 11

Author(s):

Muriel Grammont ◽

Kenneth D. Irvine

Keyword(s):

Cell Fate ◽

Null Allele ◽

Somatic Cells ◽

Ectopic Expression ◽

Notch Receptor ◽

Drosophila Oogenesis ◽

Early Stages ◽

Polar Cell ◽

Hypomorphic Alleles ◽

Notch Activation

fringe encodes a glycosyltransferase that modulates the ability of the Notch receptor to be activated by its ligands. We describe studies of fringe function during early stages of Drosophila oogenesis. Animals mutant for hypomorphic alleles of fringe contain follicles with an incorrect number of germline cells, which are separated by abnormally long and disorganized stalks. Analysis of clones of somatic cells mutant for a null allele of fringe localizes the requirement for fringe in follicle formation to the polar cells, and demonstrates that fringe is required for polar cell fate. Clones of cells mutant for Notch also lack polar cells and the requirement for Notch in follicle formation appears to map to the polar cells. Ectopic expression of fringe or of an activated form of Notch can generate an extra polar cell. Our results indicate that fringe plays a key role in positioning Notch activation during early oogenesis, and establish a function for the polar cells in separating germline cysts into individual follicles.

Download Full-text

A molecular basis for transdetermination in Drosophila imaginal discs: interactions between wingless and decapentaplegic signaling

Development ◽

10.1242/dev.125.1.115 ◽

1998 ◽

Vol 125 (1) ◽

pp. 115-124

Author(s):

L. Maves ◽

G. Schubiger

Keyword(s):

Cell Fate ◽

Molecular Basis ◽

Regulatory Element ◽

Ectopic Expression ◽

Wing Development ◽

Downstream Target ◽

Leg Development ◽

Disc Cells ◽

Targeted Expression ◽

Necessary And Sufficient

We are investigating how Drosophila imaginal disc cells establish and maintain their appendage-specific determined states. We have previously shown that ectopic expression of wingless (wg) induces leg disc cells to activate expression of the wing marker Vestigial (Vg) and transdetermine to wing cells. Here we show that ectopic wg expression non-cell-autonomously induces Vg expression in leg discs and that activated Armadillo, a cytosolic transducer of the Wg signal, cell-autonomously induces Vg expression in leg discs, indicating that this Vg expression is directly activated by Wg signaling. We find that ubiquitous expression of wg in leg discs can induce only dorsal leg disc cells to express Vg and transdetermine to wing. Dorsal leg disc cells normally express high levels of decapentaplegic (dpp) and its downstream target, optomotor-blind (omb). We find that high levels of dpp expression, which are both necessary and sufficient for dorsal leg development, are required for wg-induced transdetermination. We show that dorsalization of ventral leg disc cells, through targeted expression of either dpp or omb, is sufficient to allow wg to induce Vg expression and wing fate. Thus, dpp and omb promote both dorsal leg cell fate as well as transdetermination-competent leg disc cells. Taken together, our results show that the Wg and Dpp signaling pathways cooperate to induce Vg expression and leg-towing transdetermination. We also show that a specific vg regulatory element, the vg boundary enhancer, is required for transdetermination. We propose that an interaction between Wg and Dpp signaling can explain why leg disc cells transdetermine to wing and that our results have implications for normal leg and wing development.

Download Full-text

Ectopic expression of either the Drosophila gooseberry-distal or proximal gene causes alterations of cell fate in the epidermis and central nervous system

Development ◽

10.1242/dev.120.5.1151 ◽

1994 ◽

Vol 120 (5) ◽

pp. 1151-1161 ◽

Cited By ~ 21

Author(s):

Y. Zhang ◽

A. Ungar ◽

C. Fresquez ◽

R. Holmgren

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Cell Fate ◽

Ectopic Expression ◽

Cell Fate Specification ◽

Single Function ◽

Independent Functions ◽

Segment Polarity ◽

The Central Nervous System ◽

The Common

Previous studies have shown that the segment polarity locus gooseberry, which contains two closely related transcripts gooseberry-proximal and gooseberry-distal, is required for proper development in both the epidermis and the central nervous system of Drosophila. In this study, the roles of the gooseberry proteins in the process of cell fate specification have been examined by generating two fly lines in which either gooseberry-distal or gooseberry-proximal expression is under the control of an hsp70 promoter. We have found that ectopic expression of either gooseberry protein causes cell fate transformations that are reciprocal to those of a gooseberry deletion mutant. Our results suggest that the gooseberry-distal protein is required for the specification of naked cuticle in the epidermis and specific neuroblasts in the central nervous system. These roles may reflect independent functions in neuroblasts and epidermal cells or a single function in the common ectodermal precursor cells. The gooseberry-proximal protein is also found in the same neuroblasts as gooseberry-distal and in the descendants of these cells.

Download Full-text

Identifying targets of the rough homeobox gene of Drosophila: evidence that rhomboid functions in eye development

Development ◽

10.1242/dev.116.2.335 ◽

1992 ◽

Vol 116 (2) ◽

pp. 335-346 ◽

Cited By ~ 26

Author(s):

M. Freeman ◽

B.E. Kimmel ◽

G.M. Rubin

Keyword(s):

Cell Fate ◽

Target Genes ◽

Eye Development ◽

Expression Patterns ◽

Ectopic Expression ◽

Homeobox Gene ◽

Homeodomain Protein ◽

Dorsoventral Patterning ◽

Altered Expression ◽

Enhancer Trap Lines

In order to identify potential target genes of the rough homeodomain protein, which is known to specify some aspects of the R2/R5 photoreceptor subtype in the Drosophila eye, we have carried out a search for enhancer trap lines whose expression is rough-dependent. We crossed 101 enhancer traps that are expressed in the developing eye into a rough mutant background, and have identified seven lines that have altered expression patterns. One of these putative rough target genes is rhomboid, a gene known to be required for dorsoventral patterning and development of some of the nervous system in the embryo. We have examined the role of rhomboid in eye development and find that, while mutant clones have only a subtle phenotype, ectopic expression of the gene causes the non-neuronal mystery cells to be transformed into photoreceptors. We propose that rhomboid is a part of a partially redundant network of genes that specify photoreceptor cell fate.

Download Full-text

In vivo analysis using variants of zebrafish BMPR-IA: range of action and involvement of BMP in ectoderm patterning

Development ◽

10.1242/dev.126.1.181 ◽

1999 ◽

Vol 126 (1) ◽

pp. 181-190 ◽

Cited By ~ 8

Author(s):

M. Nikaido ◽

M. Tada ◽

H. Takeda ◽

A. Kuroiwa ◽

N. Ueno

Keyword(s):

Cell Fate ◽

Transforming Growth Factor Beta ◽

Transforming Growth Factor ◽

Active Form ◽

Ectopic Expression ◽

Signal Propagation ◽

Early Embryo ◽

Type I ◽

Cell Fate Conversion

It has been an intriguing problem whether the polypeptide growth factors belonging to the transforming growth factor-beta (TGF-beta) superfamily function as direct and long-range signaling molecules in pattern formation of the early embryo. In this study, we examined the mechanism of signal propagation of bone morphogenetic protein (BMP) in the ectodermal patterning of zebrafish embryos, in which BMP functions as an epidermal inducer and a neural inhibitor. To estimate the effective range of zbmp-2, we first performed whole-mount in situ hybridization analysis. The zbmp-2-expressing domain and the neuroectoderm, marked by otx-2 expression, were complementary, suggesting that BMP has a short-range effect in vivo. Moreover, mosaic experiments using a constitutively active form of a zebrafish BMP type I receptor (CA-BRIA) demonstrated that the cell-fate conversion, revealed by ectopic expression of gata-3 and repression of otx-2, occurred in a cell-autonomous manner, denying the involvement of the relay mechanism. We also found that zbmp-2 was induced cell autonomously within the transplanted cells in the host ectoderm, suggesting that BMP cannot influence even the neighboring cells. This result is consistent with the observation that there is no gap between the expression domains of zbmp-2 and otx-2. Taken together, we propose that, in ectodermal patterning, BMP exerts a direct and cell-autonomous effect to fate uncommitted ectodermal cells to become epidermis.

Download Full-text

Intestinal Neurod1 expression impairs paneth cell differentiation and promotes enteroendocrine lineage specification

Scientific Reports ◽

10.1038/s41598-019-55292-7 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Hui Joyce Li ◽

Subir K. Ray ◽

Ning Pan ◽

Jody Haigh ◽

Bernd Fritzsch ◽

...

Keyword(s):

Cell Differentiation ◽

Epithelial Cells ◽

Cell Fate ◽

Intestinal Epithelial Cells ◽

Paneth Cell ◽

Substantial Reduction ◽

Ectopic Expression ◽

Cell Lineage ◽

Intestinal Epithelial ◽

Conditional Expression

AbstractTranscription factor Neurod1 is required for enteroendocrine progenitor differentiation and maturation. Several earlier studies indicated that ectopic expression of Neurod1 converted non- neuronal cells into neurons. However, the functional consequence of ectopic Neurod1 expression has not been examined in the GI tract, and it is not known whether Neurod1 can similarly switch cell fates in the intestine. We generated a mouse line that would enable us to conditionally express Neurod1 in intestinal epithelial cells at different stages of differentiation. Forced expression of Neurod1 throughout intestinal epithelium increased the number of EECs as well as the expression of EE specific transcription factors and hormones. Furthermore, we observed a substantial reduction of Paneth cell marker expression, although the expressions of enterocyte-, tuft- and goblet-cell specific markers are largely not affected. Our earlier study indicated that Neurog3+ progenitor cells give rise to not only EECs but also Goblet and Paneth cells. Here we show that the conditional expression of Neurod1 restricts Neurog3+ progenitors to adopt Paneth cell fate, and promotes more pronounced EE cell differentiation, while such effects are not seen in more differentiated Neurod1+ cells. Together, our data suggest that forced expression of Neurod1 programs intestinal epithelial cells more towards an EE cell fate at the expense of the Paneth cell lineage and the effect ceases as cells mature to EE cells.

Download Full-text

Suppression of HGF receptor gene expression by oxidative stress is mediated through the interplay between Sp1 and Egr-1

AJP Renal Physiology ◽

10.1152/ajprenal.00426.2002 ◽

2003 ◽

Vol 284 (6) ◽

pp. F1216-F1225 ◽

Cited By ~ 32

Author(s):

Xianghong Zhang ◽

Youhua Liu

Keyword(s):

Oxidative Stress ◽

Epithelial Cells ◽

Collecting Duct ◽

Receptor Gene ◽

Ectopic Expression ◽

Transcriptional Activator ◽

Physical Interaction ◽

Nucleotide Position ◽

Renal Epithelial Cells ◽

Cis Acting

Hepatocyte growth factor (HGF) receptor, the product of the c-metprotooncogene, is transcriptionally regulated by a wide variety of cytokines as well as extracellular environmental cues. In this report, we demonstrate that c-met expression was significantly suppressed by oxidative stress. Treatment of mouse renal inner medullary collecting duct epithelial cells with 0.5 mM H2O2inhibited c-met mRNA and protein expression, which was concomitant with induction of Egr-1 transcription factor. Ectopic expression of Egr-1 in renal epithelial cells markedly inhibited endogenous c-met expression in a dose-dependent fashion, suggesting a causative effect of Egr-1 in mediating c-met suppression. The cis-acting element responsible for H2O2-induced c-met inhibition was localized at nucleotide position −223 to −68 of c-met promoter, in which reside an imperfect Egr-1 and three Sp1-binding sites. Egr-1 markedly suppressed c-met promoter activity but did not directly bind to its cis-acting element in the c-met gene. Induction of Egr-1 by oxidative stress attenuated the binding of Sp1 to its cognate sites, but it did not affect Sp1 abundance in renal epithelial cells. Immunoprecipitation uncovered that Egr-1 physically interacted with Sp1 by forming the Sp1/Egr-1 complex, which presumably resulted in a decreased availability of unbound Sp1 as a transcriptional activator for the c-met gene. Thus it appears that inhibition of c-met expression by oxidative stress is mediated by the interplay between Sp1 and Egr-1 transcription factors. Our findings reveal a novel transcriptional regulatory mechanism by which Egr-1 sequesters Sp1 as a transcriptional activator of c-met via physical interaction.

Download Full-text