Biomedical subjects

H R Horvitz

Publications and source records attributed to H R Horvitz.

At least 73 records · Page 4Linked to original sources

PubMed1996

The Caenorhabditis elegans gene lin-17, which is required for certain asymmetric cell divisions, encodes a putative seven-transmembrane protein similar to the Drosophila frizzled protein.

Mutations in the gene lin-17 result in the disruption of a variety of asymmetric cell divisions in Caenorhabditis elegans. We have found that lin-17 encodes a protein with seven putative transmembrane domains. The LIN-17 protein is most similar to the Drosophila Frizzled protein and its vertebrate homologs. Studies using a lin-17-green fluorescent protein translational fusion indicate that lin-17 is expressed in mother cells before asymmetric cell divisions and in both daughter cells after the divisions. Our results suggest that lin-17 encodes a receptor that regulates the polarities of cells undergoing asymmetric cell divisions and raise the possibility that the LIN-17 protein acts as a receptor for the Wnt protein LIN-44, which also controls asymmetric cell divisions.

Amino Acid Sequence↗

PubMed1996

Transcriptional regulator of programmed cell death encoded by Caenorhabditis elegans gene ces-2.

The ces (for cell-death specification) genes of the nematode Caenorhabditis elegans control the cell-death fate of individual cell types and are candidates for being the regulators of an evolutionarily conserved general pathway of programmed cell death. Here we present what we believe is the first molecular characterization of a ces gene. We cloned the gene ces-2, which is required to activate programmed cell death in the sister cells of the serotoninergic neurosecretory motor (NSM) neurons, and found that ces-2 encodes a basic region leucine-zipper (bZIP) transcription factor. The CES-2 protein is most similar to members of the PAR (proline- and acid-rich) subfamily of bZIP proteins and has DNA-binding specificity like that of PAR-family proteins. An oncogenic form of the mammalian PAR-family protein, hepatic leukaemia factor (HLF), is reported to effect programmed cell death in mammalian cells. On the basis of these observations, we suggest that some CES-2/PAR family transcription factors are evolutionary conserved regulators of programmed cell death.

Amino Acid Sequence↗

PubMed1996

The Caenorhabditis elegans gene sem-4 controls neuronal and mesodermal cell development and encodes a zinc finger protein.

Neuronal and mesodermal cell types are generated in separate cell lineages during the larval development of Caenorhabditis elegans. Here we demonstrate that the gene sem-4 is required in both types of lineages for the normal development of neuronal and mesodermal cell types. The sem-4 gene encodes a protein containing seven zinc finger motifs of the C2H2 class, four of which are arranged in two pairs widely separated in the primary sequence of the protein. These pairs of zinc fingers are similar to pairs of zinc fingers in the protein encoded by the Drosophila homeotic gene spalt and in the human transcription factor PRDII-BF1. Analysis of sem-4 alleles suggests that different zinc fingers in the SEM-4 protein may function differentially in neuronal and mesodermal cell types. We propose that sem-4 interacts with different transcription factors in different cell types to control the transcription of genes that function in the processes of neuronal and mesodermal cell development.

Alleles↗

PubMed1996

An alternatively spliced C. elegans ced-4 RNA encodes a novel cell death inhibitor.

The C. elegans gene ced-4 is essential for programmed cell death. We report that ced-4 encodes two transcripts and that whereas the major transcript can cause programmed cell death, the minor transcript can act oppositely and prevent programmed cell death, thus defining a novel class of cell death inhibitors. That ced-4 has both cell-killing and cell-protective functions is consistent with previous genetic studies. Our results suggest that the dual protective and killer functions of the C. elegans bcl-2-like gene ced-9 are mediated by inhibition of the killer and protective ced-4 functions, respectively. We propose that a balance between opposing ced-4 functions influences the decision of a cell to live or to die by programmed cell death and that both ced-9 and ced-4 protective functions are required to prevent programmed cell death.

Alleles↗

PubMed1996

The Caenorhabditis elegans cell-death protein CED-3 is a cysteine protease with substrate specificities similar to those of the human CPP32 protease.

The Caenorhabditis elegans cell-death gene ced-3 encodes a protein similar to mammalian interleukin-1beta-converting enzyme (ICE), a cysteine protease implicated in mammalian apoptosis. We show that the full-length CED-3 protein undergoes proteolytic activation to generate a CED-3 cysteine protease and that CED-3 protease activity is required for killing cells by programmed cell death in C. elegans. We developed an easy and general method for the purification of CED-3/ICE-like proteases and used this method to facilitate a comparison of the substrate specificities of four different purified cysteine proteases. We found that in its substrate preferences CED-3 was more similar to the mammalian CPP32 protease than to mammalian ICE or NEDD2/ICH-1 protease. Our results suggest that different mammalian CED-3/ICE-like proteases may have distinct roles in mammalian apoptosis and that CPP32 is a candidate for being a mammalian functional equivalent of CED-3.

Amino Acid Sequence↗

PubMed1996

Developing Caenorhabditis elegans neurons may contain both cell-death protective and killer activities.

We developed a method for examining the effects of overexpressing cell-death-related genes in specific Caenorhabditis elegans neurons that normally live. Using this method, we demonstrated that the cell-death genes ced-3, ced-4, and ced-9 all can act cell autonomously to control programmed cell death. Our observations indicate further that not only the protective activity of ced-9 but also the killer activities of ced-3 and ced-4 are likely to be present in cells that normally live. We propose that both in C. elegans and in other organisms a competition between antagonistic protective and killer activities determines whether specific cells will live or die. Our results suggest a genetic pathway for programmed cell death in C. elegans in which ced-4 acts upstream of or in parallel to ced-3 and ced-9 negatively regulates the activity of ced-4.

Animals↗

PubMed1996

EGL-10 regulates G protein signaling in the C. elegans nervous system and shares a conserved domain with many mammalian proteins.

The frequencies of certain periodic behaviors of the nematode C. elegans are regulated in a dose-dependent manner by the activity of the gene egl-10. These behaviors are modulated oppositely by the activity of the G protein alpha subunit gene goa-1, suggesting that egl-10 may regulate a G protein signaling pathway in a dose-dependent fashion. egl-10 encodes a protein similar to Sst2p, a negative regulator of G protein signaling in yeast. EGL-10 protein is localized in neural processes, where it may function in neurotransmitter signaling. Two previously known and 13 newly identified mammalian genes have similarity to egl-10 and SST2, and we propose that members of this family regulate many G protein signaling pathways.

Alleles↗

PubMed1996

Three novel mutations and two variants in the gene for Cu/Zn superoxide dismutase in familial amyotrophic lateral sclerosis.

Autosomal dominant inheritance is exhibited by about 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by the death of motor neurons in the brain and spinal cord. A subgroup of these familial cases are linked to mutations in the gene which codes for Cu/Zn superoxide dismutase (SOD1). We report three additional mutations occurring in the SOD1 gene in ALS patients and two single base pair variant changes. The single base pair change in an ALS family causes a glycine 93 to valine substitution, which is the fifth distinct amino acid change reported for the glycine 93 residue. One missense mutation in exon 5 would substitute neutral valine for the negatively-charged aspartate 124 (aspartate 124 to valine). An individual with an apparently sporadic case of ALS carries a three base pair deletion in exon 5 of the SOD1 gene. These three mutations bring to 38 the total number of distinct SOD1 mutations associated with familial ALS.

Amyotrophic Lateral Sclerosis↗

PubMed1996

The Caenorhabditis elegans behavioral gene unc-24 encodes a novel bipartite protein similar to both erythrocyte band 7.2 (stomatin) and nonspecific lipid transfer protein.

We report here the positional cloning and molecular characterization of the unc-24 gene of Caenorhabditis elegans. This gene is required for normal locomotion and interacts with genes that affect the worm's response to volatile anesthetics. The predicted gene product contains a domain similar to part of two ion channel regulators (the erythrocyte integral membrane protein stomatin and the C. elegans neuronal protein MEC-2) juxtaposed to a domain similar to nonspecific lipid transfer protein (nsLTP; also called sterol carrier protein 2). Sequence analysis suggests that the nsLTP-like domain of UNC-24 provides lipid carrier function and is tethered to the plasma membrane by the stomatin-like domain which may be regulatory. We postulate that UNC-24 may be involved in lipid transfer between closely apposed membranes.

ADP-Ribosylation Factors↗

PubMed1996

The Caenorhabditis elegans LIN-26 protein is required to specify and/or maintain all non-neuronal ectodermal cell fates.

The C. elegans gene lin-26, which encodes a presumptive zinc-finger transcription factor, is required for hypodermal cells to acquire their proper fates. Here we show that lin-26 is expressed not only in all hypodermal cells but also in all glial-like cells. During asymmetric cell divisions that generate a neuronal cell and a non-neuronal cell, LIN-26 protein is symmetrically segregated and then lost from the neuronal cell. Expression in glial-like cells (socket and sheath cells) is biologically important, as some of these neuronal support cells die or seem sometimes to be transformed to neuron-like cells in embryos homozygous for strong loss-of-function mutations. In addition, most of these glial-like cells are structurally and functionally defective in animals carrying the weak loss-of-function mutation lin-26(n156). lin-26 mutant phenotypes and expression patterns together suggest that lin-26 is required to specify and/or maintain the fates not only of hypodermal cells but also of all other non-neuronal ectodermal cells in C. elegans. We speculate that lin-26 acts by repressing the expression of neuronal-specific genes in non-neuronal cells.

Animals↗

PubMed1995

The ksr-1 gene encodes a novel protein kinase involved in Ras-mediated signaling in C. elegans.

By screening for mutations that suppress the vulval defects caused by a constitutively active let-60 ras gene, we identified six loss-of-function alleles of ksr-1, a novel C. elegans gene. Our genetic analysis showed ksr-1 positively mediates Ras signaling and functions downstream of or in parallel to let-60. In the absence of ksr-1 function, normal Ras signaling is impaired only slightly, suggesting ksr-1 may act to modulate, or in a branch that diverges from, the main signaling pathway. The predicted KSR-1 protein has a protein kinase domain and is most similar to a recently identified Drosophila protein involved in Ras signaling. We propose that the function of ksr-1 is evolutionarily conserved.

Amino Acid Sequence↗

PubMed1995

The Caenorhabditis elegans gene lin-1 encodes an ETS-domain protein and defines a branch of the vulval induction pathway.

The Caenorhabditis elegans gene lin-1 appears to act after the Ras-Raf-MEK-MAPK signaling cascade that mediates vulval induction. We show that lin-1 is a negative regulator of vulval cell fates and encodes an ETS-domain putative transcription factor containing potential MAPK phosphorylation sites. In lin-1 null mutants, the vulval precursor cells (VPCs) still respond to signaling from the gonadal anchor cell, indicating that lin-1 defines a branch of the inductive signaling pathway. We also provide evidence that the inductive and lateral signaling pathways are integrated to control the 1 degree and 2 degrees vulval cell fates after the point at which lin-1 acts in the inductive pathway and that VPCs can assess the relative rather than absolute levels of inductive and lateral signaling in determining whether to express the 1 degree or 2 degrees vulval cell fates.

Amino Acid Sequence↗

PubMed1995

An FGF receptor signaling pathway is required for the normal cell migrations of the sex myoblasts in C. elegans hermaphrodites.

The sex myoblasts (SMs) in C. elegans hermaphrodites undergo anteriorly directed cell migrations that allow for the proper localization of the egg-laying muscles. These migrations are controlled in part by a signal emanating from gonadal cells that allows the SMs to be attracted to their precise final positions flanking the center of the gonad. Mutations in egl-15 alter the nature of the interaction between the gonad and the SMs, resulting in the posterior displacement of the SMs. Here we show that egl-15 encodes a receptor tyrosine kinase of the fibroblast growth factor receptor (FGFR) subfamily with multiple roles in development. Three genes were identified that behave genetically as activators or mediators of egl-15 activity. One of these genes, sem-5, encodes an adaptor molecule that transduces signals from a variety of receptor tyrosine kinases. Like egl-15 and sem-5, the other two genes may similarly act in FGFR signaling pathways in C. elegans.

Amino Acid Sequence↗

PubMed1995

Defective recycling of synaptic vesicles in synaptotagmin mutants of Caenorhabditis elegans.

Synaptotagmin, an integral membrane protein of the synaptic vesicle, binds calcium and interacts with proteins of the plasma membrane. These observations suggest several possible functions for synaptotagmin in synaptic vesicle dynamics: it could facilitate exocytosis by promoting calcium-dependent fusion, inhibit exocytosis by preventing fusion, or facilitate endocytosis of synaptic vesicles from the plasma membrane by acting as a receptor for the endocytotic proteins of the clathrin AP2 complex. Here we show that synaptic vesicles are depleted at synaptic terminals in synaptotagmin mutants of the nematode Caenorhabditis elegans. This depletion is not caused by a defect in transport or by increased synaptic vesicle release, but rather by a defect in retrieval or synaptic vesicles from the plasma membrane. Thus we propose that, as well as being involved in exocytosis, synaptotagmin functions in vesicular recycling.

Aldicarb↗

PubMed1995

The C. elegans gene lin-44, which controls the polarity of certain asymmetric cell divisions, encodes a Wnt protein and acts cell nonautonomously.

Mutations in the C. elegans gene lin-44 lead to reversals in the polarity of certain asymmetric cell divisions. We have discovered that lin-44 is a member of the Wnt family of genes, which encode secretory glycoproteins implicated in intercellular signaling. Both in situ hybridization experiments using lin-44 transcripts and experiments using reporter constructs designed to mimic patterns of lin-44 expression indicate that lin-44 is expressed in hypodermal cells at the tip of the tail and posterior to the cells with polarities affected by lin-44 mutations. Our mosaic analysis indicates that lin-44 acts cell nonautonomously. We propose that LIN-44 protein is secreted by tail hypodermal cells and affects the polarity of asymmetric cell divisions that occur more anteriorly in the tail.

Amino Acid Sequence↗

PubMed1995

Inhibition of the Caenorhabditis elegans cell-death protease CED-3 by a CED-3 cleavage site in baculovirus p35 protein.

The baculovirus protein p35 inhibits programmed cell death in such diverse animals as insects, nematodes and mammals. Here we show that p35 protein is a substrate for and inhibitor of the Caenorhabditis elegans cell-death protease CED-3 (refs 6, 7) and a substrate for four CED-3-like vertebrate cysteine protease activities implicated in apoptosis in mammals. A p35 mutation that greatly reduced p35 activity in vitro as a CED-3 substrate and inhibitor abolished p35 activity in vivo in protecting against cell death in C. elegans. Introduction of the CED-3 cleavage site in p35 into the cowpox virus protein crmA, which inhibits mammalian apoptosis but not programmed cell death in C. elegans, caused crmA to block CED-3-mediated cell death. These observations suggest that p35 may prevent programmed cell death in C. elegans and other species by acting as a competitive inhibitor of cysteine proteases.

Amino Acid Sequence↗

PubMed1995

Patterning of the Caenorhabditis elegans head region by the Pax-6 family member vab-3.

The Pax-6 genes are important for eye development in both vertebrates and Drosophila. Mutations in the human PAX6 gene are found in patients with a variety of eye disorders, including aniridia and Peters' anomaly, and mutations in the Drosophila Pax-6 homologue cause the eyeless phenotype. In the nematode Caenorhabditis elegans, vab-3 mutants display many defects in head-region development, including aberrant morphogenesis, transformation of hypodermal (epidermal-like) cell fates to those of posterior homologues, and abnormal specification of neurons. Here we show that vab-3 is a member of the paired-domain-containing Pax-6 gene family and is expressed in head-region cells. This C. elegans Pax-6 locus can also encode proteins lacking the paired domain. Our results suggest that a primordial role of the Pax-6 gene family could have been to pattern part of the head region, and that Pax-6 genes subsequently evolved to be more specifically involved in eye development.

Amino Acid Sequence↗

PubMed1995

The Caenorhabditis elegans gene mek-2 is required for vulval induction and encodes a protein similar to the protein kinase MEK.

An evolutionarily conserved signal transduction pathway that utilizes a receptor tyrosine kinase and a Ras protein mediates the induction of vulval cell fates in the nematode Caenorhabditis elegans. We sought new genes that function in this pathway by screening for suppressors of the Multivulva phenotype caused by a mutation that activates the let-60 ras gene. Seven such suppressor mutations defined a new gene involved in vulval induction. We named this gene mek-2, because its predicted protein product is most similar to MEK, a protein-serine/threonine and tyrosine kinase. mek-2 mutations can be arranged in an allelic series. A probable null mutation eliminated vulval induction, and the strongest mutations alter codons conserved in most or all protein kinases. Our genetic analysis showed that mek-2 functions downstream of let-60 ras and is required for ras-mediated signal transduction in vivo. The MEK-2 protein may interact with the products of the lin-45 raf and mpk-1 MAP kinase genes, which also mediate vulval induction.

Amino Acid Sequence↗