Search PubMed⌕ Search

Biomedical subjects

H Robert Horvitz

Publications and source records attributed to H Robert Horvitz.

At least 19 recordsLinked to original sources
PubMed2006

C. elegans SIR-2.1 interacts with 14-3-3 proteins to activate DAF-16 and extend life span.

The longevity of Caenorhabditis elegans is promoted by extra copies of the sir-2.1 gene in a manner dependent on the forkhead transcription factor DAF-16. We identify two C. elegans 14-3-3 proteins as SIR-2.1 binding partners and show that 14-3-3 genes are required for the life-span extension conferred by extra copies of sir-2.1. 14-3-3 proteins are also required for SIR-2.1-induced transcriptional activation of DAF-16 and stress resistance. Following heat stress, SIR-2.1 can bind DAF-16 in a 14-3-3-dependent manner. By contrast, low insulin-like signaling does not promote SIR-2.1/DAF-16 interaction, and sir-2.1 and the 14-3-3 genes are not required for the regulation of life span by the insulin-like signaling pathway. We propose the existence of a stress-dependent pathway in which SIR-2.1 and 14-3-3 act in parallel to the insulin-like pathway to activate DAF-16 and extend life span.

14-3-3 Proteins↗
PubMed2006

C. elegans ISWI and NURF301 antagonize an Rb-like pathway in the determination of multiple cell fates.

The class A, B and C synthetic multivulva (synMuv) genes act redundantly to negatively regulate the expression of vulval cell fates in Caenorhabditis elegans. The class B and C synMuv proteins include homologs of proteins that modulate chromatin and influence transcription in other organisms similar to members of the Myb-MuvB/dREAM, NuRD and Tip60/NuA4 complexes. To determine how these chromatin-remodeling activities negatively regulate the vulval cell-fate decision, we isolated a suppressor of the synMuv phenotype and found that the suppressor gene encodes the C. elegans homolog of Drosophila melanogaster ISWI. The C. elegans ISW-1 protein likely acts as part of a Nucleosome Remodeling Factor (NURF) complex with NURF-1, a nematode ortholog of NURF301, to promote the synMuv phenotype. isw-1 and nurf-1 mutations suppress both the synMuv phenotype and the multivulva phenotype caused by overactivation of the Ras pathway. Our data suggest that a NURF-like complex promotes the expression of vulval cell fates by antagonizing the transcriptional and chromatin-remodeling activities of complexes similar to Myb-MuvB/dREAM, NuRD and Tip60/NuA4. Because the phenotypes caused by a null mutation in the tumor-suppressor and class B synMuv gene lin-35 Rb and a gain-of-function mutation in let-60 Ras are suppressed by reduction of isw-1 function, NURF complex proteins might be effective targets for cancer therapy.

Adenosine Triphosphatases↗
PubMed2006

The short coiled-coil domain-containing protein UNC-69 cooperates with UNC-76 to regulate axonal outgrowth and normal presynaptic organization in Caenorhabditis elegans.

BACKGROUND: The nematode Caenorhabditis elegans has been used extensively to identify the genetic requirements for proper nervous system development and function. Key to this process is the direction of vesicles to the growing axons and dendrites, which is required for growth-cone extension and synapse formation in the developing neurons. The contribution and mechanism of membrane traffic in neuronal development are not fully understood, however. RESULTS: We show that the C. elegans gene unc-69 is required for axon outgrowth, guidance, fasciculation and normal presynaptic organization. We identify UNC-69 as an evolutionarily conserved 108-amino-acid protein with a short coiled-coil domain. UNC-69 interacts physically with UNC-76, mutations in which produce similar defects to loss of unc-69 function. In addition, a weak reduction-of-function allele, unc-69(ju69), preferentially causes mislocalization of the synaptic vesicle marker synaptobrevin. UNC-69 and UNC-76 colocalize as puncta in neuronal processes and cooperate to regulate axon extension and synapse formation. The chicken UNC-69 homolog is highly expressed in the developing central nervous system, and its inactivation by RNA interference leads to axon guidance defects. CONCLUSION: We have identified a novel protein complex, composed of UNC-69 and UNC-76, which promotes axonal growth and normal presynaptic organization in C. elegans. As both proteins are conserved through evolution, we suggest that the mammalian homologs of UNC-69 and UNC-76 (SCOCO and FEZ, respectively) may function similarly.

Animals↗
PubMed2006

Identification and classification of genes that act antagonistically to let-60 Ras signaling in Caenorhabditis elegans vulval development.

The synthetic multivulva (synMuv) genes negatively regulate Ras-mediated vulval induction in the nematode Caenorhabditis elegans. The synMuv genes define three classes, A, B, and C, such that double mutants carrying mutations in genes of any two classes are multivulva. The class B synMuv genes include lin-35, a homolog of the retinoblastoma (Rb) tumor suppressor gene, as well as homologs of genes that function with Rb in transcriptional regulation. We screened for additional synMuv mutations using a strategy different from that of previous synMuv genetic screens. Some of the mutations we recovered affect new synMuv genes. We present criteria for assigning synMuv mutations into different genetic classes. We also describe the molecular characterization of the class B synMuv gene lin-65.

Alleles↗
PubMed2006

No association of DYNC1H1 with sporadic ALS in a case-control study of a northern European derived population: a tagging SNP approach.

The cytoplasmic dynein-dynactin complex has been implicated in the aetiology of motor neuron degeneration in both mouse models and human forms of motor neuron disease. We have previously shown that mutations in the cytoplasmic dynein 1 heavy chain 1 gene (Dync1h1) are causal in a mouse model of late-onset motor neuron degeneration but have found no association of the homologous sites in human DYNC1H1 with human motor neuron disease. Here we extend these analyses to investigate the DYNC1H1 genomic locus to determine if it is associated with sporadic amyotrophic lateral sclerosis (ALS) in a northern European-derived population. Among the 16 single nucleotide polymorphisms (SNPs) we examined, just two SNPs (rs2251644 and rs941793) were sufficient to tag the majority of haplotypic variation (r2 > or = 0.85) and these were tested in a case-control association study with 266 North American sporadic ALS patients and 225 matched controls. We found no association between genetic variation at DYNC1H1 and sporadic ALS (rs2251644; p = 0.538, rs941793; p = 0.204, haplotype; p = 0.956). In addition we investigated patterns of diversity at DYNC1H1 in Japanese and Cameroonian populations to establish the evolutionary history for this gene and observed reduced genetic diversity in the northern Europeans suggestive of selection at this locus.

Amyotrophic Lateral Sclerosis↗
PubMed2005

C. elegans HAM-1 positions the cleavage plane and regulates apoptosis in asymmetric neuroblast divisions.

Asymmetric cell division occurs when a mother cell divides to generate two distinct daughter cells, a process that promotes the generation of cellular diversity in metazoans. During Caenorhabditis elegans development, the asymmetric divisions of neural progenitors generate neurons, neural support cells and apoptotic cells. C. elegans HAM-1 is an asymmetrically distributed cortical protein that regulates several of these asymmetric neuroblast divisions. Here, we show that HAM-1 is a novel protein and define residues important for HAM-1 function and distribution to the cell cortex. Our phenotypic analysis of ham-1 mutant embryos suggests that HAM-1 controls only neuroblast divisions that produce apoptotic cells. Moreover, ham-1 mutant embryos contain many unusually large cell-death corpses. An investigation of this corpse phenotype revealed that it results from a reversal of neuroblast polarity. A misplacement of the neuroblast cleavage plane generates daughter cells of abnormal size, with the apoptotic daughters larger than normal. Thus, HAM-1 regulates the position of the cleavage plane, apoptosis and mitotic potential in C. elegans asymmetric cell divisions.

Alleles↗
PubMed2005

lin-8, which antagonizes Caenorhabditis elegans Ras-mediated vulval induction, encodes a novel nuclear protein that interacts with the LIN-35 Rb protein.

Ras-mediated vulval development in C. elegans is inhibited by the functionally redundant sets of class A, B, and C synthetic Multivulva (synMuv) genes. Three of the class B synMuv genes encode an Rb/DP/E2F complex that, by analogy with its mammalian and Drosophila counterparts, has been proposed to silence genes required for vulval specification through chromatin modification and remodeling. Two class A synMuv genes, lin-15A and lin-56, encode novel nuclear proteins that appear to function as a complex. We show that a third class A synMuv gene, lin-8, is the defining member of a novel C. elegans gene family. The LIN-8 protein is nuclear and can interact physically with the product of the class B synMuv gene lin-35, the C. elegans homolog of mammalian Rb. LIN-8 likely acts with the synMuv A proteins LIN-15A and LIN-56 in the nucleus, possibly in a protein complex with the synMuv B protein LIN-35 Rb. Other LIN-8 family members may function in similar complexes in different cells or at different stages. The nuclear localization of LIN-15A, LIN-56, and LIN-8, as well as our observation of a direct physical interaction between class A and class B synMuv proteins, supports the hypothesis that the class A synMuv genes control vulval induction through the transcriptional regulation of gene expression.

Amino Acid Sequence↗
PubMed2005

MicroRNA expression profiles classify human cancers.

Recent work has revealed the existence of a class of small non-coding RNA species, known as microRNAs (miRNAs), which have critical functions across various biological processes. Here we use a new, bead-based flow cytometric miRNA expression profiling method to present a systematic expression analysis of 217 mammalian miRNAs from 334 samples, including multiple human cancers. The miRNA profiles are surprisingly informative, reflecting the developmental lineage and differentiation state of the tumours. We observe a general downregulation of miRNAs in tumours compared with normal tissues. Furthermore, we were able to successfully classify poorly differentiated tumours using miRNA expression profiles, whereas messenger RNA profiles were highly inaccurate when applied to the same samples. These findings highlight the potential of miRNA profiling in cancer diagnosis.

Animals↗
PubMed2005

MicroRNA expression in zebrafish embryonic development.

MicroRNAs (miRNAs) are small noncoding RNAs, about 21 nucleotides in length, that can regulate gene expression by base-pairing to partially complementary mRNAs. Regulation by miRNAs can play essential roles in embryonic development. We determined the temporal and spatial expression patterns of 115 conserved vertebrate miRNAs in zebrafish embryos by microarrays and by in situ hybridizations, using locked-nucleic acid-modified oligonucleotide probes. Most miRNAs were expressed in a highly tissue-specific manner during segmentation and later stages, but not early in development, which suggests that their role is not in tissue fate establishment but in differentiation or maintenance of tissue identity.

Animals↗
PubMed2005

Chimeric mutations in the M2 segment of the 5-hydroxytryptamine-gated chloride channel MOD-1 define a minimal determinant of anion/cation permeability.

The ionic selectivity of ligand-gated ion channels (LGICs) determines whether receptor activation produces an excitatory or inhibitory response. The determinants of anion/cation selectivity were investigated for a new member of the LGIC superfamily, MOD-1, a serotonin-gated chloride channel cloned from the nematode Caenorhabditis elegans. In common with other anionic LGICs (glycine receptors and GABA(A) receptors), the selectivity triple mutant in the pore-forming M2 segment (proline insertion, Ala --> Glu substitution at the central ring, and Thr --> Val at the hydrophobic ring) converted the selectivity of MOD-1 from anionic to cationic. Unlike other LGICs, however, this mutant in MOD-1 was highly selective for K+ over other cations. Subsets of this selectivity triple mutant were studied to define the minimal change required for conversion from anion-permeable to cation-permeable. The double mutant at the central ring of charge (deltaPro-269/A270E) produced a non-selective cation channel. Charge reversal at the central ring alone (A270E) was sufficient to convert MOD-1 to cation-permeable. These results refine the determinants of ion-charge selectivity in LGICs and demonstrate the critical role of the central ring of charge formed by the M2 segments.

Alanine↗
PubMed2005

Tyramine Functions independently of octopamine in the Caenorhabditis elegans nervous system.

Octopamine biosynthesis requires tyrosine decarboxylase to convert tyrosine into tyramine and tyramine beta-hydroxylase to convert tyramine into octopamine. We identified and characterized a Caenorhabditis elegans tyrosine decarboxylase gene, tdc-1, and a tyramine beta-hydroxylase gene, tbh-1. The TBH-1 protein is expressed in a subset of TDC-1-expressing cells, indicating that C. elegans has tyraminergic cells that are distinct from its octopaminergic cells. tdc-1 mutants have behavioral defects not shared by tbh-1 mutants. We show that tyramine plays a specific role in the inhibition of egg laying, the modulation of reversal behavior, and the suppression of head oscillations in response to anterior touch. We propose a model for the neural circuit that coordinates locomotion and head oscillations in response to anterior touch. Our findings establish tyramine as a neurotransmitter in C. elegans, and we suggest that tyramine is a genuine neurotransmitter in other invertebrates and possibly in vertebrates as well.

Amino Acid Sequence↗
PubMed2005

The let-7 MicroRNA family members mir-48, mir-84, and mir-241 function together to regulate developmental timing in Caenorhabditis elegans.

The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the hbl-1 3' UTR and downregulating hbl-1 activity. Genetic analysis indicates that mir-48, mir-84, and mir-241 specify the timing of the L2-to-L3 transition in parallel to the heterochronic genes lin-28 and lin-46. These results indicate that let-7 family microRNAs function in combination to affect both early and late developmental timing decisions.

Animals↗
PubMed2004

Microarray analysis of microRNA expression in the developing mammalian brain.

BACKGROUND: MicroRNAs are a large new class of tiny regulatory RNAs found in nematodes, plants, insects and mammals. MicroRNAs are thought to act as post-transcriptional modulators of gene expression. In invertebrates microRNAs have been implicated as regulators of developmental timing, neuronal differentiation, cell proliferation, programmed cell death and fat metabolism. Little is known about the roles of microRNAs in mammals. RESULTS: We isolated 18-26 nucleotide RNAs from developing rat and monkey brains. From the sequences of these RNAs and the sequences of the rat and human genomes we determined which of these small RNAs are likely to have derived from stem-loop precursors typical of microRNAs. Next, we developed a microarray technology suitable for detecting microRNAs and printed a microRNA microarray representing 138 mammalian microRNAs corresponding to the sequences of the microRNAs we cloned as well as to other known microRNAs. We used this microarray to determine the profile of microRNAs expressed in the developing mouse brain. We observed a temporal wave of expression of microRNAs, suggesting that microRNAs play important roles in the development of the mammalian brain. CONCLUSION: We describe a microarray technology that can be used to analyze the expression of microRNAs and of other small RNAs. MicroRNA microarrays offer a new tool that should facilitate studies of the biological roles of microRNAs. We used this method to determine the microRNA expression profile during mouse brain development and observed a temporal wave of gene expression of sequential classes of microRNAs.

Animals↗
PubMed2004

The Caenorhabditis elegans F-box protein SEL-10 promotes female development and may target FEM-1 and FEM-3 for degradation by the proteasome.

The Caenorhabditis elegans F-box protein SEL-10 and its human homolog have been proposed to regulate LIN-12 Notch signaling by targeting for ubiquitin-mediated proteasomal degradation LIN-12 Notch proteins and SEL-12 PS1 presenilins, the latter of which have been implicated in Alzheimer's disease. We found that sel-10 is the same gene as egl-41, which previously had been defined by gain-of-function mutations that semidominantly cause masculinization of the hermaphrodite soma. Our results demonstrate that mutations causing loss-of-function of sel-10 also have masculinizing activity, indicating that sel-10 functions to promote female development. Genetically, sel-10 acts upstream of the genes fem-1, fem-2, and fem-3 and downstream of her-1 and probably tra-2. When expressed in mammalian cells, SEL-10 protein coimmunoprecipitates with FEM-1, FEM-2, and FEM-3, which are required for masculinization, and FEM-1 and FEM-3 are targeted by SEL-10 for proteasomal degradation. We propose that SEL-10-mediated proteolysis of FEM-1 and FEM-3 is required for normal hermaphrodite development.

Animals↗
PubMed2004

The engulfment process of programmed cell death in caenorhabditis elegans.

Programmed cell death involves the removal of cell corpses by other cells in a process termed engulfment. Genetic studies of the nematode Caenorhabditis elegans have led to a framework not only for the killing step of programmed cell death but also for the process of cell-corpse engulfment. This work has defined two signal transduction pathways that act redundantly to control engulfment. Signals expressed by dying cells probably regulate these C. elegans pathways. Components of the cell-corpse recognition system of one of the C. elegans pathways include the CED-7 ABC transporter, which likely presents a death ligand on the surface of the dying cell; the CED-1 transmembrane receptor, which recognizes this signal; and the CED-6 adaptor protein, which may transduce a signal from CED-1. The second C. elegans pathway acts in parallel and involves a novel Rac GTPase signaling pathway, with the components CED-2 CrkII, CED-5 DOCK180, CED-12 ELMO, and CED-10 Rac. The cell-corpse recognition system that activates this pathway remains to be characterized. In C. elegans, and possibly in mammals, the process of cell-corpse engulfment promotes the death process itself. The known mechanisms for cell-corpse engulfment leave much to be discovered concerning this fundamental aspect of metazoan biology.

Animals↗
PubMed2003

sup-9, sup-10, and unc-93 may encode components of a two-pore K+ channel that coordinates muscle contraction in Caenorhabditis elegans.

Genetic studies of sup-9, unc-93, and sup-10 strongly suggest that these genes encode components of a multi-subunit protein complex that coordinates muscle contraction in Caenorhabditis elegans. We cloned sup-9 and sup-10 and found that they encode a two-pore K+ channel and a novel transmembrane protein, respectively. We also found that UNC-93 and SUP-10 colocalize with SUP-9 within muscle cells, and that UNC-93 is a member of a novel multigene family that is conserved among C. elegans, Drosophila, and humans. Our results indicate that SUP-9 and perhaps other two-pore K+ channels function as multiprotein complexes, and that UNC-93 and SUP-10 likely define new classes of ion channel regulatory proteins.

Amino Acid Sequence↗