scholarly journals The Role of Sevenless in Drosophila R7 Photoreceptor Specification

2019 ◽  
Author(s):  
Andrew Tomlinson ◽  
Yannis Emmanuel Mavromatakis ◽  
Ronald Arias
Keyword(s):  
Receptor Tyrosine Kinase ◽  
Gene Function ◽  
Target Gene ◽  
Egf Receptor ◽  
Transmembrane Domain ◽  
Current Model ◽  
Intracellular Domain ◽  
Hydrophobic Domain ◽  
Pathway Activation

AbstractSevenless (Sev) is a Receptor Tyrosine Kinase (RTK) that is required for the specification of the Drosophila R7 photoreceptor. Other Drosophila photoreceptors are specified by the action of another RTK; the Drosophila EGF Receptor (DER). Why Sev is required specifically in the R7 precursor, and the exact role it plays in the cell’s fate assignment have long remained unclear. Notch (N) signaling plays many roles in R7 specification, one of which is to prevent DER activity from establishing the photoreceptor fate. Our current model of Sev function is that it hyperactivates the RTK pathway in the R7 precursor to overcome in the N-imposed block on photoreceptor specification. From this perspective DER and Sev are viewed as engaging the same transduction machinery, the only difference between them being the level of pathway activation that they induce. To test this model, we generated a Sev/DER chimera in which the intracellular domain of Sev is replaced with that of DER. This chimerical receptor acts indistinguishably from Sev itself; a result that is entirely consistent with the two RTKs sharing identical transduction abilities. A long-standing question in regard to Sev is the function of a hydrophobic domain some 60 amino acids from the initiating Methionine. If this represents a transmembrane domain, it would endow Sev with N-terminal intracellular sequences through which it could engage internal transduction pathways. However, we find that this domain acts as an internal signal peptide, and that there is no Sev N-terminal intracellular domain. phyllopod (phyl) is the target gene of the RTK pathway, and we show that R7 precursors are selectively lost when phyl gene function is mildly compromised, and that other photoreceptors are removed when the gene function is further reduced. This result adds a key piece of evidence for the hyperactivation of the RTK pathway in the R7 precursor. To facilitate the hyperactivation of the RTK pathway, Sev is expressed at high levels. However, when we express DER at the levels at which Sev is expressed, strong gain-of-function effects result, consistent with ligand-independent activation of the receptor. This highlights another key feature of Sev; that it is expressed at high levels yet remains strictly ligand dependent. Finally, we find that activated Sev can rescue R3/4 photoreceptors when their DER function is abrogated. These results are collectively consistent with Sev and DER activating the same transduction machinery, with Sev generating a pathway hyperactivation to overcome the N-imposed block to photoreceptor specification in R7 precursors.

Interaction between Drosophila EGF receptor and vnd determines three dorsoventral domains of the neuroectoderm

Development ◽  
1998 ◽  
Vol 125 (18) ◽  
pp. 3625-3633 ◽  
Author(s):  
Y. Yagi ◽  
T. Suzuki ◽  
S. Hayashi
Keyword(s):  
Map Kinase ◽  
Receptor Tyrosine Kinase ◽  
Egf Receptor ◽  
Regulatory Region ◽  
Homeobox Gene ◽  
Kinase Activation ◽  
Intermediate Column ◽  
Kinase Signaling Pathway ◽  
Map Kinase Signaling Pathway

Neurogenesis in Drosophila melanogaster starts by an ordered appearance of neuroblasts arranged in three columns (medial, intermediate and lateral) in each side of the neuroectoderm. Here we show that, in the intermediate column, the receptor tyrosine kinase DER represses expression of proneural genes, achaete and scute, and is required for the formation of neuroblasts. Most of the early function of DER is likely to be mediated by the Ras-MAP kinase signaling pathway, which is activated in the intermediate column, since a loss of a component of this pathway leads to a phenotype identical to that in DER mutants. MAP-kinase activation was also observed in the medial column where esg and proneural gene expression is unaffected by DER. We found that the homeobox gene vnd is required for the expression of esg and scute in the medial column, and show that vnd acts through the negative regulatory region of the esg enhancer that mediates the DER signal, suggesting the role of vnd is to counteract DER-dependent repression. Thus nested expression of vnd and the DER activator rhomboid is crucial to subdivide the neuroectoderm into the three dorsoventral domains.

scholarly journals Rotational Coupling of the Transmembrane and Kinase Domains of the Neu Receptor Tyrosine Kinase

2000 ◽  
Vol 11 (10) ◽  
pp. 3589-3599 ◽  
Author(s):  
Charlotte A. Bell ◽  
John A. Tynan ◽  
Kristen C. Hart ◽  
April N. Meyer ◽  
Scott C. Robertson ◽  
...  
Keyword(s):  
Receptor Tyrosine Kinase ◽  
Tyrosine Kinases ◽  
Transmembrane Domain ◽  
Growth Factor Receptor ◽  
Kinase Domain ◽  
Receptor Dimerization ◽  
Activating Mutations ◽  
Rotational Coupling ◽  
Specific Orientation

Ligand binding to receptor tyrosine kinases (RTKs) regulates receptor dimerization and activation of the kinase domain. To examine the role of the transmembrane domain in regulation of RTK activation, we have exploited a simplified transmembrane motif, [VVVEVVV]n, previously shown to activate the Neu receptor. Here we demonstrate rotational linkage of the transmembrane domain with the kinase domain, as evidenced by a periodic activation of Neu as the dimerization motif is shifted across the transmembrane domain. These results indicate that activation requires a specific orientation of the kinase domains with respect to each other. Results obtained with platelet-derived growth factor receptor-β suggest that this rotational linkage of the transmembrane domain to the kinase domain may be a general feature of RTKs. These observations suggest that activating mutations in RTK transmembrane and juxtamembrane domains will be limited to those residues that position the kinase domains in an allowed rotational conformation.

scholarly journals MicroRNA-497-5p stimulates osteoblast differentiation through HMGA2-mediated JNK signaling pathway

2020 ◽  
Author(s):  
Huiqing Zhao ◽  
Yexiang Yang ◽  
Yang Wang ◽  
Xiaolei Feng ◽  
Adi Deng ◽  
...  
Keyword(s):  
Osteoblast Differentiation ◽  
Target Gene ◽  
Therapeutic Option ◽  
High Mobility ◽  
Nodule Formation ◽  
Mineral Density ◽  
Jnk Pathway ◽  
Pathway Activation ◽  
Jnk Signaling Pathway

Abstract Background: Osteoporosis (OP) has the characteristics of the decline in bone mineral density and worsening of bone quality, contributing to higher risk of fractures. Some microRNAs (miRNAs) have been validated as possible mediators of osteoblast differentiation. We herein aimed to clarify whether miR-497-5p regulates differentiation of osteoblasts in MC3T3-E1 cells.Methods: The expression of miR-497-5p in OP patients and controls was measured by RT-qPCR, and its expression changes during osteoblast differentiation were determined as well. The effects of miR-497-5p on differentiation of MC3T3-E1 cells were studied using MTT, ALR staining and ARS staining. The target gene of miR-497-5p was predicted by TargetScan, and the effects of its target gene on differentiation and the pathway involved were investigated.Results: miR-497-5p expression expressed poorly in OP patients and its expression was upregulated during MC3T3-E1 cell differentiation. Overexpression of miR-497-5p promoted mineralized nodule formation and the expression of RUNX2 and OCN. miR-497-5p targeted high mobility group AT-Hook 2 (HMGA2), while upregulation of HMGA2 inhibited osteogenesis induced by miR-497-5p mimic. miR-497-5p significantly impaired the c-Jun NH2-terminal kinase (JNK) pathway, whereas HMGA2 activated this pathway. Activation of the JNK pathway inhibited the stimulative role of miR-497-5p mimic in osteogenesis.Conclusions: miR-497-5p inhibits development of OP by hampering osteogenesis via targeting HMGA2. We hence conclude that targeting miR-497-5p might be an attractive therapeutic option for OP.

scholarly journals MicroRNA-497-5p stimulates osteoblast differentiation through HMGA2-mediated JNK signaling pathway

2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Huiqing Zhao ◽  
Yexiang Yang ◽  
Yang Wang ◽  
Xiaolei Feng ◽  
Adi Deng ◽  
...  
Keyword(s):  
Osteoblast Differentiation ◽  
Target Gene ◽  
High Mobility ◽  
Nodule Formation ◽  
Mineral Density ◽  
Jnk Pathway ◽  
Jnk Signaling ◽  
Pathway Activation ◽  
Jnk Signaling Pathway

Abstract Background Osteoporosis (OP) has the characteristics of the decline in bone mineral density and worsening of bone quality, contributing to a higher risk of fractures. Some microRNAs (miRNAs) have been validated as possible mediators of osteoblast differentiation. We herein aimed to clarify whether miR-497-5p regulates the differentiation of osteoblasts in MC3T3-E1 cells. Methods The expression of miR-497-5p in OP patients and controls was measured by RT-qPCR, and its expression changes during osteoblast differentiation were determined as well. The effects of miR-497-5p on the differentiation of MC3T3-E1 cells were studied using MTT, ALR staining, and ARS staining. The target gene of miR-497-5p was predicted by TargetScan, and the effects of its target gene on differentiation and the pathway involved were investigated. Results miR-497-5p expressed poorly in OP patients, and its expression was upregulated during MC3T3-E1 cell differentiation. Overexpression of miR-497-5p promoted mineralized nodule formation and the expression of RUNX2 and OCN. miR-497-5p targeted high mobility group AT-Hook 2 (HMGA2), while the upregulation of HMGA2 inhibited osteogenesis induced by miR-497-5p mimic. miR-497-5p significantly impaired the c-Jun NH2-terminal kinase (JNK) pathway, whereas HMGA2 activated this pathway. Activation of the JNK pathway inhibited the stimulative role of miR-497-5p mimic in osteogenesis. Conclusions miR-497-5p inhibits the development of OP by promoting osteogenesis via targeting HMGA2.

Mechanism of enhancement of slow delayed rectifier current by extracellular sulfhydryl modification

1997 ◽  
Vol 273 (1) ◽  
pp. H208-H219 ◽  
Author(s):  
J. A. Yao ◽  
M. Jiang ◽  
G. N. Tseng
Keyword(s):  
Transmembrane Domain ◽  
Ventricular Myocytes ◽  
Current Model ◽  
The Other ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Sh Group ◽  
Intracellular Ca ◽  
Sulfhydryl Modification

To explore the role of sulfhydryl (SH) groups in the function of cardiac slow delayed rectifier channels, we tested the effects of extracellular thimerosal (TMS, a hydrophilic SH modifier) on slow delayed rectifier current (IKs) induced by human IsK (hIsK) in oocytes and on the native IKs in canine ventricular myocytes. TMS (25 or 50 microM) had similar effects on the two currents: current amplitude increased, and there was an acceleration of activation and a slowing of deactivation. These effects showed little or no reversal after washout of TMS. The effects did not depend on intracellular Ca release or protein kinase activities but could be suppressed by dithiothreitol pretreatment. According to the current model of transmembrane topology, there is no cystein in the extracellular domain of hIsK. A likely candidate for TMS modification is the SH group on another subunit in oocyte cell membrane that interacts with IsK to form a functional channel. To explore the domain of hIsK involved in the interaction, extracellular serines of hIsK were mutated to cysteines at three locations: S37C (close to the transmembrane domain), S4C (close to the NH2-terminus), and S28C (in between). S37C and S28C mutations did not affect channel properties or hIsK response to TMS. On the other hand, S4C mutation reduced current expression even when S4C cRNA was injected at a quantity 50-fold higher than that of the other three proteins. Importantly, the response to TMS was markedly reduced in S4C compared with the other three proteins. Therefore, the NH2-terminus of hIsK may be involved in hIsK interaction with the SH-bearing subunit, and this interaction modulates slow delayed rectifier channel function.

scholarly journals CHOP-Dependent Stress-Inducible Expression of a Novel Form of Carbonic Anhydrase VI

1999 ◽  
Vol 19 (1) ◽  
pp. 495-504 ◽  
Author(s):  
John Sok ◽  
Xiao-Zhong Wang ◽  
Nikoleta Batchvarova ◽  
Masahiko Kuroda ◽  
Heather Harding ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Target Gene ◽  
Target Genes ◽  
Direct Evidence ◽  
Nuclear Protein ◽  
Intracellular Form ◽  
Carbonic Anhydrase Vi ◽  
Responsive Element

ABSTRACT CHOP (also called GADD153) is a stress-inducible nuclear protein that dimerizes with members of the C/EBP family of transcription factors and was initially identified as an inhibitor of C/EBP binding to classic C/EBP target genes. Subsequent experiments suggested a role for CHOP-C/EBP heterodimers in positively regulating gene expression; however, direct evidence that this is the case has so far not been uncovered. Here we describe the identification of a positively regulated direct CHOP-C/EBP target gene, that encoding murine carbonic anhydrase VI (CA-VI). The stress-inducible form of the gene is expressed from an internal promoter and encodes a novel intracellular form of what is normally a secreted protein. Stress-induced expression of CA-VI is both CHOP and C/EBPβ dependent in that it does not occur in cells deficient in either gene. A CHOP-responsive element was mapped to the inducibleCA-VI promoter, and in vitro footprinting revealed binding of CHOP-C/EBP heterodimers to that site. Rescue of CA-VIexpression in c/ebpβ−/− cells by exogenous C/EBPβ and a shorter, normally inhibitory isoform of the protein known as LIP suggests that the role of the C/EBP partner is limited to targeting the CHOP-containing heterodimer to the response element and points to a preeminent role for CHOP in CA-VI induction during stress.

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