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1.
Previous studies have shown that a synthetic multivulva phenotype results from mutations in genes that antagonize the ras-mediated intercellular signaling system responsible for vulval induction in Caenorhabditis elegans. Synthetic multivulva mutations define two classes of genes, A and B, and a mutation in a gene of each class is required to produce the multivulva phenotype. The ectopic vulval tissue in multivulva animals is generated by vulval precursor cells that in the wild type do not generate vulval tissue. One of the class B synthetic multivulva genes, lin-35, encodes a protein similar to the retinoblastoma (Rb) protein. In this article, we describe the isolation and characterization of 50 synthetic multivulva mutations, the identification of new components of both the class A and class B lin-35 Rb pathways, and the cloning of lin-52, a class B gene that may have a conserved role in Rb-mediated signaling. 相似文献
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The Let-60 Locus Controls the Switch between Vulval and Nonvulval Cell Fates in Caenorhabditis Elegans 总被引:11,自引:4,他引:7
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During induction of the Caenorhabditis elegans hermaphrodite vulva by the anchor cell of the gonad, six multipotent vulval precursor cells (VPCs) have two distinct fates: three VPCs generate the vulva and the other three VPCs generate nonspecialized hypodermis. Genes that control the fates of the VPCs in response to the anchor cell signal are defined by mutations that cause all six VPCs to generate vulval tissue (Multivulva or Muv) or that cause all six VPCs to generate hypodermis (Vulvaless or Vul). Seven dominant Vul mutations were isolated as dominant suppressors of a lin-15 Muv mutation. These mutations are dominant alleles of the gene let-60, previously identified only by recessive lethal mutations. Our genetic studies of these dominant Vul recessive lethal mutations, recessive lethal mutations, intragenic revertants of the dominant Vul mutations, and the closely mapping semi-dominant multivulva lin-34 mutations suggest that: (1) loss-of-function mutations of let-60 are recessive lethal at a larval stage, but they also cause a Vul phenotype if the lethality is rescued maternally by a lin-34 gain-of-function mutation. (2) The dominant Vul alleles of let-60 are dominant negative mutations whose gene products compete with wild-type activity. (3) lin-34 semidominant Muv alleles are either gain-of-function mutations of let-60 or gain-of-function mutations of an intimately related gene that elevates let-60 activity. We propose that let-60 activity controls VPC fates. In a wild-type animal, reception by a VPC of inductive signal activates let-60, and it generates into a vulval cell type; in absence of inductive signal, let-60 activity is low and the VPC generates hypodermal cells. Our genetic interaction studies suggest that let-60 acts downstream of let-23 and lin-15 and upstream of lin-1 and lin-12 in the genetic pathway specifying the switch between vulval and nonvulval cell types. 相似文献
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Genetic and Phenotypic Studies of Hypomorphic Lin-12 Mutants in Caenorhabditis Elegans 总被引:1,自引:1,他引:0
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The lin-12 gene of Caenorhabditis elegans is thought to encode a receptor for intercellular signals that specify certain cell fates during development. We describe several alleles of lin-12 that reduce but do not eliminate lin-12 activity (hypomorphic alleles). These alleles cause a novel egg-laying defective (Egl) phenotype in hermaphrodites as well as incompletely penetrant cell fate transformations seen with high penetrance in lin-12 null mutants. Characterization of the Egl phenotype revealed additional roles of lin-12 in the development of the egg-laying system that were not apparent from studying lin-12 null mutants: lin-12 activity is required for proper early vulval morphogenesis as well as for some unknown later aspect of egg-laying system development. Reversion of the Egl phenotype caused by one lin-12 hypomorphic allele was used to identify potential interacting genes as described in the accompanying paper. 相似文献
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By screening for suppressors of hypomorphic mutations of let-23, a receptor tyrosine kinase necessary for vulval induction in Caenorhabditis elegans, we recovered >/=12 mutations defining the sli-1 (suppressor of lineage defect) locus. sli-1 mutations suppress four of five phenotypes associated with hypomorphic alleles of let-23 but do not suppress let-23 null alleles. Thus, a sli-1 mutation does not bypass the requirement for functional let-23 but rather allows more potent LET-23-dependent signaling. Mutations at the sli-1 locus are otherwise silent with respect to vulval differentiation and cause only a low-penetrance abnormal head phenotype. Mutations at sli-1 also suppress the vulval defects but not other defects associated with mutations of sem-5, whose product likely interacts with LET-23 protein during vulval induction. Mutations at sli-1 suppress lin-2, lin-7 and lin-10 mutations but only partially suppress lin-3 and let-60 mutations and do not suppress a lin-45 mutation. The sli-1 locus displays dosage sensitivity: severe reduction of function alleles of sli-1 are semidominant suppressors; a duplication of the sli-1 (+) region enhances the vulvaless phenotype of hypomorphic mutations of let-23. We propose that sli-1 is a negative regulator that acts at or near the LET-23-mediated step of the vulval induction pathway. Our analysis suggests that let-23 can activate distinct signaling pathways in different tissues: one pathway is required for vulval induction; another pathway is involved in hermaphrodite fertilty and is not regulated by sli-1. 相似文献
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The Caenorhabditis elegans vulva develops from the progeny of three vulval precursor cells (VPCs) induced to divide and differentiate by a signal from the somatic gonad. Evolutionarily conserved Ras and Notch extracellular signaling pathways are known to function during this process. To identify novel loci acting in vulval development, we carried out a genetic screen for mutants having a protruding-vulva (Pvl) mutant phenotype. Here we report the initial genetic characterization of several novel loci: bar-1, pvl-4, pvl-5, and pvl-6. In addition, on the basis of their Pvl phenotypes, we show that the previously identified genes lin-26, mom-3/mig-14, egl-18, and sem-4 also function during vulval development. Our characterization indicates that (1) pvl-4 and pvl-5 are required for generation/survival of the VPCs; (2) bar-1, mom-3/mig-14, egl-18, and sem-4 play a role in VPC fate specification; (3) lin-26 is required for proper VPC fate execution; and (4) pvl-6 acts during vulval morphogenesis. In addition, two of these genes, bar-1 and mom-3/mig-14, are known to function in processes regulated by Wnt signaling, suggesting that a Wnt signaling pathway is acting during vulval development. 相似文献
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The protein kinase Raf is an important signaling protein. Raf activation is initiated by an interaction with GTP-bound Ras, and Raf functions in signal transmission by phosphorylating and activating a mitogen-activated protein (MAP) kinase kinase named MEK. We identified 13 mutations in the Caenorhabditis elegans lin-45 raf gene by screening for hermaphrodites with abnormal vulval formation or germline function. Weak, intermediate, and strong loss-of-function or null mutations were isolated. The phenotype caused by the most severe mutations demonstrates that lin-45 is essential for larval viability, fertility, and the induction of vulval cell fates. The lin-45(null) phenotype is similar to the mek-2(null) and mpk-1(null) phenotypes, indicating that LIN-45, MEK-2, and MPK-1 ERK MAP kinase function in a predominantly linear signaling pathway. The lin-45 alleles include three missense mutations that affect the Ras-binding domain, three missense mutations that affect the protein kinase domain, two missense mutations that affect the C-terminal 14-3-3 binding domain, three nonsense mutations, and one small deletion. The analysis of the missense mutations indicates that Ras binding, 14-3-3-binding, and protein kinase activity are necessary for full Raf function and suggests that a 14-3-3 protein positively regulates Raf-mediated signaling during C. elegans development. 相似文献
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gon-14 functions with class B and class C synthetic multivulva genes to control larval growth in Caenorhabditis elegans 总被引:3,自引:0,他引:3
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Previous work showed that C. elegans gon-14 is required for gonadogenesis. Here we report that gon-14 encodes a protein with similarity to LIN-15B, a class B synMuv protein. An extensive region of GON-14 contains blocks of sequence similarity to transposases of the hAT superfamily, but key residues are not conserved, suggesting a distant relationship. GON-14 also contains a putative THAP DNA-binding domain. A rescuing gon-14::GON-14::VENUS reporter is broadly expressed during development and localizes to the nucleus. Strong loss-of-function and predicted null gon-14 alleles have pleiotropic defects, including multivulval (Muv) defects and temperature-sensitive larval arrest. Although the gon-14 Muv defect is not enhanced by synMuv mutations, gon-14 interacts genetically with class B and class C synMuv genes, including lin-35/Rb, let-418/Mi-2beta, and trr-1/TRRAP. The gon-14; synMuv double mutants arrest as larvae when grown under conditions supporting development to adulthood for the respective single mutants. The gon-14 larval arrest is suppressed by loss of mes-2/E(Z), mes-6/ESC, or mes-4, which encodes a SET domain protein. Additionally, gon-14 affects expression of pgl-1 and lag-2, two genes regulated by the synMuv genes. We suggest that gon-14 functions with class B and class C synMuv genes to promote larval growth, in part by antagonizing MES-2,3,6/ESC-E(z) and MES-4. 相似文献
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The Caenorhabditis elegans class A and B synthetic multivulva (synMuv) genes redundantly antagonize an EGF/Ras pathway to prevent ectopic vulval induction. We identify a class A synMuv mutation in the promoter of the lin-3 EGF gene, establishing that lin-3 is the key biological target of the class A synMuv genes in vulval development and that the repressive activities of the class A and B synMuv pathways are integrated at the level of lin-3 expression. Using FISH with single mRNA molecule resolution, we find that lin-3 EGF expression is tightly restricted to only a few tissues in wild-type animals, including the germline. In synMuv double mutants, lin-3 EGF is ectopically expressed at low levels throughout the animal. Our findings reveal that the widespread ectopic expression of a growth factor mRNA at concentrations much lower than that in the normal domain of expression can abnormally activate the Ras pathway and alter cell fates. These results suggest hypotheses for the mechanistic basis of the functional redundancy between the tumor-suppressor-like class A and B synMuv genes: the class A synMuv genes either directly or indirectly specifically repress ectopic lin-3 expression; while the class B synMuv genes might function similarly, but alternatively might act to repress lin-3 as a consequence of their role in preventing cells from adopting a germline-like fate. Analogous genes in mammals might function as tumor suppressors by preventing broad ectopic expression of EGF-like ligands. 相似文献
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The combined action of two intercellular signaling pathways specifies three cell fates during vulval induction in C. elegans 总被引:11,自引:0,他引:11
Each of the six C. elegans vulval precursor cells (VPCs) has three potential fates (1 degree, 2 degrees, or 3 degrees). The fate of each VPC depends on two types of signals: a graded inductive signal that acts at a distance and a short-range lateral signal among the VPCs. We describe interactions among mutations that cause different misspecifications of VPC fates. Particular combinations of mutations cause all six VPCs to have a single fate independent of their positions. Our results suggest that specification of the three VPC fates is accomplished by two binary decisions, each effected by one of the two signaling pathways. The gene lin-12 acts in the lateral signaling pathway and specifies 2 degrees. The "vulvaless" and "multivulva" genes act in the inductive signaling pathway and specify 1 degree independently of lin-12 and 2 degrees via lin-12. We describe a model for the regulatory circuitry underlying VPC determination that includes a role for lin-12 in both autocrine and paracrine VPC signaling. 相似文献
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Loss of LIN-35, the Caenorhabditis elegans ortholog of the tumor suppressor p105Rb, results in enhanced RNA interference 总被引:2,自引:0,他引:2
Lehner B Calixto A Crombie C Tischler J Fortunato A Chalfie M Fraser AG 《Genome biology》2006,7(1):R4-10
Background
Genome-wide RNA interference (RNAi) screening is a very powerful tool for analyzing gene function in vivo in Caenorhabditis elegans. The effectiveness of RNAi varies from gene to gene, however, and neuronally expressed genes are largely refractive to RNAi in wild-type worms.Results
We found that C. elegans strains carrying mutations in lin-35, the worm ortholog of the tumor suppressor gene p105Rb, or a subset of the genetically related synMuv B family of chromatin-modifying genes, show increased strength and penetrance for many germline, embryonic, and post-embryonic RNAi phenotypes, including neuronal RNAi phenotypes. Mutations in these same genes also enhance somatic transgene silencing via an RNAi-dependent mechanism. Two genes, mes-4 and zfp-1, are required both for the vulval lineage defects resulting from mutations in synMuv B genes and for RNAi, suggesting a common mechanism for the function of synMuv B genes in vulval development and in regulating RNAi. Enhanced RNAi in the germline of lin-35 worms suggests that misexpression of germline genes in somatic cells cannot alone account for the enhanced RNAi observed in this strain.Conclusion
A worm strain with a null mutation in lin-35 is more sensitive to RNAi than any other previously described single mutant strain, and so will prove very useful for future genome-wide RNAi screens, particularly for identifying genes with neuronal functions. As lin-35 is the worm ortholog of the mammalian tumor suppressor gene p105Rb, misregulation of RNAi may be important during human oncogenesis. 相似文献16.
The Caenorhabditis elegans gene lin-36 acts to antagonize Ras-mediated vulval induction in a pathway that includes genes with products similar to the mammalian retinoblastoma (Rb) protein and the Rb-binding protein p48. We report that lin-36 encodes a novel protein of 962 amino acids. We demonstrate that lin-36 functions in and is expressed in the vulval precursor cells, establishing that the lin-36 pathway is involved in intercellular signaling. We also report that the lin-36 pathway and/or another pathway that is functionally redundant with the lin-36 pathway antagonize a ligand-independent activity of the receptor tyrosine kinase/Ras vulval induction pathway. 相似文献
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Null mutations in lin-35, the Caenorhabditis elegans ortholog of the mammalian Rb protein, cause no obvious morphological defects. Using a genetic approach to identify genes that may function redundantly with lin-35, we have isolated a mutation in the C. elegans psa-1 gene. lin-35; psa-1 double mutants display severe developmental defects leading to early larval arrest and adult sterility. The psa-1 gene has previously been shown to encode a C. elegans homolog of yeast SWI3, a critical component of the SWI/SNF complex, and has been shown to regulate asymmetric cell divisions during C. elegans development. We observed strong genetic interactions between psa-1 and lin-35 as well as a subset of the class B synMuv genes that include lin-37 and lin-9. Loss-of-function mutations in lin-35, lin-37, and lin-9 strongly enhanced the defects of asymmetric T cell division associated with a psa-1 mutation. Our results suggest that LIN-35/Rb and a certain class B synMuv proteins collaborate with the SWI/SNF protein complex to regulate the T cell division as well as other events essential for larval growth. 相似文献
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Egg-laying defective mutants of the nematode Caenorhabditis elegans 总被引:11,自引:0,他引:11
We have isolated 145 fertile mutants of C. elegans that are defective in egg laying and have characterized 59 of them genetically, behaviorally and pharmacologically. These 59 mutants define 40 new genes called egl. for egg-laying abnormal. Most of the other mutants are defective in previously identified genes. The egl mutants differ with respect to the severity of their egg-laying defects and the presence of behavioral or morphological pleiotropies. We have defined four distinct categories of mutants based on their responses to the pharmacological agents serotonin and imipramine, which stimulate egg laying by wild-type hermaphrodites. These drugs test the functioning of the vulva, the vulval and uterine muscles and the hermaphrodite-specific neurons (HSNs), which innervate the vulval muscles. Mutants representing 14 egl genes fail to respond to serotonin and to imipramine and are likely to be defective in the functioning of the vulva or the vulval and uterine muscles. Four mutants (representing four different genes) lay eggs in response to serotonin but not to imipramine and appear to be egg-laying defective because of defects in the HSNs; three of these four were selected specifically for these drug responses. Mutants representing seven egl genes lay eggs in response to serotonin and to imipramine. One egl mutant responds to imipramine but not to serotonin. The remaining egl mutants show variable or intermediate responses to the drugs. Two of the HSN-defective mutants, egl-1 and her-1(n695), lack HSN cell bodies and are likely to be expressing the normally male-specific program of HSN cell death. Whereas egl-1 animals appear to be defective specifically in HSN development, her-1(n695) animals exhibit multiple morphological pleiotropies, displaying partial transformation of the sexual phenotype of many cells and tissues. At least two of the egl mutants appear to be defective in the processing of environmental signals that modulate egg laying and may define new components of the neural circuitry that control egg laying. 相似文献
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Basolateral Localization of the Caenorhabditis elegans Epidermal Growth Factor Receptor in Epithelial Cells by the PDZ Protein LIN-10
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Charles W. Whitfield Claire Bnard Tom Barnes S. Hekimi Stuart K. Kim 《Molecular biology of the cell》1999,10(6):2087-2100
In Caenorhabditis elegans, the EGF receptor (encoded by let-23) is localized to the basolateral membrane domain of the epithelial vulval precursor cells, where it acts through a conserved Ras/MAP kinase signaling pathway to induce vulval differentiation. lin-10 acts in LET-23 receptor tyrosine kinase basolateral localization, because lin-10 mutations result in mislocalization of LET-23 to the apical membrane domain and cause a signaling defective (vulvaless) phenotype. We demonstrate that the previous molecular identification of lin-10 was incorrect, and we identify a new gene corresponding to the lin-10 genetic locus. lin-10 encodes a protein with regions of similarity to mammalian X11/mint proteins, containing a phosphotyrosine-binding and two PDZ domains. A nonsense lin-10 allele that truncates both PDZ domains only partially reduces lin-10 gene activity, suggesting that these protein interaction domains are not essential for LIN-10 function in vulval induction. Immunocytochemical experiments show that LIN-10 is expressed in vulval epithelial cells and in neurons. LIN-10 is present at low levels in the cytoplasm and at the plasma membrane and at high levels at or near the Golgi. LIN-10 may function in secretion of LET-23 to the basolateral membrane domain, or it may be involved in tethering LET-23 at the basolateral plasma membrane once it is secreted. 相似文献