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Oliver Hobert

Publications and source records attributed to Oliver Hobert.

At least 19 recordsLinked to original sources
PubMed2026

FLInt in C. briggsae and C. tropicalis : Strains and resources for fast and locus-targeted integration of multi-copy transgenes.

C. briggsae and C. tropicalis are satellite model systems for molecular mechanistic investigations and for comparative studies across Caenorhabditis species. FLInt ( F luorescent L andmark Int erference) was developed in C. elegans for rapid generation of transgenic strains through integration of multi-copy DNA arrays into predetermined genomic loci, without requiring a random mutagenesis step. Here, we present resources and newly generated strains that enable FLInt in C. briggsae and C. tropicalis , yielding integrated transgenic lines within ~10 days of microinjection.

Journal Article↗
PubMed2006

Early embryonic programming of neuronal left/right asymmetry in C. elegans.

BACKGROUND: Nervous systems are largely bilaterally symmetric on a morphological level but often display striking degrees of functional left/right (L/R) asymmetry. How L/R asymmetric functional features are superimposed onto an essentially bilaterally symmetric structure and how nervous-system laterality relates to the L/R asymmetry of internal organs are poorly understood. We address these questions here by using the establishment of L/R asymmetry in the ASE chemosensory neurons of C. elegans as a paradigm. This bilaterally symmetric neuron pair is functionally lateralized in that it senses a distinct class of chemosensory cues and expresses a putative chemoreceptor family in a L/R asymmetric manner. RESULTS: We show that the directionality of the asymmetry of the two postmitotic ASE neurons ASE left (ASEL) and ASE right (ASER) in adults is dependent on a L-/R-symmetry-breaking event at a very early embryonic stage, the six-cell stage, which also establishes the L/R asymmetric placement of internal organs. However, the L/R asymmetry of the ASE neurons per se is dependent on an even earlier anterior-posterior (A/P) Notch signal that specifies embryonic ABa/ABp blastomere identities at the four-cell stage. This Notch signal, which functions through two T box genes, acts genetically upstream of a miRNA-controlled bistable feedback loop that regulates the L/R asymmetric gene-expression program in the postmitotic ASE cells. CONCLUSIONS: Our results link adult neuronal laterality to the generation of the A/P axis at the two-cell stage and raise the possibility that neural asymmetries observed across the animal kingdom are similarly established by very early embryonic interactions.

Animals↗
PubMed2006

A novel Eph receptor-interacting IgSF protein provides C. elegans motoneurons with midline guidepost function.

BACKGROUND: The ventral midline is a prominent structure in vertebrate and invertebrate nervous systems that provides crucial topological information for guiding axons to their appropriate target destinations. Rather than being composed of specialized midline glia cells as in many other species, the embryonic midline of the nematode Caenorhabditis elegans is physically defined by motoneuron cell bodies that separate the left from the right ventral cord fascicles. Their function during development, if any, is not known. RESULTS: We show here that besides being components of the postembryonic locomotory circuit, these embryonic motoneurons (eMNs) actively provide midline guidance information for a specific subset of ventral midline axons. This information is provided in the form of a novel, cell-surface-anchored immunoglobulin superfamily (IgSF) member, WRK-1. WRK-1 acts in eMNs to prevent follower axons from inappropriately crossing the ventral midline. We describe the function of the Eph receptor vab-1 and multiple ephrin ligands at the midline, and we show by double mutant analysis and physical interaction tests that WRK-1 functionally interacts with the Eph receptor system. This interaction appears to occur exclusively in the context of axon guidance at the ventral midline but not in other cellular contexts, thereby suggesting that Eph receptor signaling is mechanistically distinct in different tissue types. CONCLUSIONS: Our studies reveal cellular and molecular components of axon midline patterning and suggest that Ephrin signaling relies on previously unknown accessory components.

Animals↗
PubMed2006

Perfect seed pairing is not a generally reliable predictor for miRNA-target interactions.

We use Caenorhabditis elegans to test proposed general rules for microRNA (miRNA)-target interactions. We show that G.U base pairing is tolerated in the 'seed' region of the lsy-6 miRNA interaction with its in vivo target cog-1, and that 6- to 8-base-pair perfect seed pairing is not a generally reliable predictor for an interaction of lsy-6 with a 3' untranslated region (UTR). Rather, lsy-6 can functionally interact with its target site only in specific 3' UTR contexts. Our findings illustrate the difficulty of establishing generalizable rules of miRNA-target interactions.

3' Untranslated Regions↗
PubMed2006

An unusual Zn-finger/FH2 domain protein controls a left/right asymmetric neuronal fate decision in C. elegans.

Gene regulatory networks that control the terminally differentiated state of a cell are, by and large, only superficially understood. In a mutant screen aimed at identifying regulators of gene batteries that define the differentiated state of two left/right asymmetric C. elegans gustatory neurons, ASEL and ASER, we have isolated a mutant, fozi-1, with a novel mixed-fate phenotype, characterized by de-repression of ASEL fate in ASER. fozi-1 codes for a protein that functions in the nucleus of ASER to inhibit the expression of the LIM homeobox gene lim-6, neuropeptide-encoding genes and putative chemoreceptors of the GCY gene family. The FOZI-1 protein displays a highly unusual domain architecture, that combines two functionally essential C2H2 zinc-finger domains, which are probably involved in transcriptional regulation, with a formin homology 2 (FH2) domain, normally found only in cytosolic regulators of the actin cytoskeleton. We demonstrate that the FH2 domain of FOZI-1 has lost its actin polymerization function but maintains its phylogenetically ancient ability to homodimerize. fozi-1 genetically interacts with several transcription factors and micro RNAs in the context of specific regulatory network motifs. These network motifs endow the system with properties that provide insights into how cells adopt their stable terminally differentiated states.

Alleles↗
PubMed2006

DIG-1, a novel giant protein, non-autonomously mediates maintenance of nervous system architecture.

Dedicated mechanisms exist to maintain the architecture of an animal's nervous system after development is completed. To date, three immunoglobulin superfamily members have been implicated in this process in the nematode Caenorhabditis elegans: the secreted two-Ig domain protein ZIG-4, the FGF receptor EGL-15 and the L1-like SAX-7 protein. These proteins provide crucial information for neuronal structures, such as axons, that allows them to maintain the precise position they acquired during development. Yet, how widespread this mechanism is throughout the nervous system, and what other types of factors underlie such a maintenance mechanism, remains poorly understood. Here, we describe a new maintenance gene, dig-1, that encodes a predicted giant secreted protein containing a large number of protein interaction domains. With 13,100 amino acids, the DIG-1 protein is the largest secreted protein identifiable in any genome database. dig-1 functions post-developmentally to maintain axons and cell bodies in place within axonal fascicles and ganglia. The failure to maintain axon and cell body position is accompanied by defects in basement membrane structure, as evidenced by electron microscopy analysis of dig-1 mutants. Expression pattern and mosaic analysis reveals that dig-1 is produced by muscles to maintain nervous system architecture, demonstrating that dig-1 functions non-autonomously to preserve the proper layout of neural structures. We propose that DIG-1 is a component of the basement membrane that mediates specific contacts between cellular surfaces and their environment through the interaction with a cell-type specific set of other maintenance factors.

Animals↗
PubMed2006

Mapping functional domains of chloride intracellular channel (CLIC) proteins in vivo.

Chloride intracellular channel (CLIC) proteins are small proteins distantly related to the omega family of glutathione S-transferases (GSTs). CLIC proteins are expressed in a wide variety of tissues in multicellular organisms and are targeted to specific cellular membranes. Members of this family are capable in vitro of changing conformation from a globular, soluble state to a membrane-inserted state in which they provide chloride conductance. The structural basis for in vivo CLIC protein function, however, is not well understood. We have mapped the functional domains of CLIC family members using an in vivo assay for membrane localization and function of CLIC proteins in the nematode Caenorhabditis elegans. A<70 amino acid N-terminal domain is a key determinant of membrane localization and function of invertebrate CLIC proteins. This domain, which we term the ''PTM'' domain, named after an amphipathic putative transmembrane helix contained within it, directs distinct C. elegans CLIC homologs to distinct subcellular membranes. We find that within the PTM region, the cysteine residues required for GST-type activity are unnecessary for invertebrate CLIC function, but that specific residues within the proposed transmembrane helix are necessary for correct targeting and protein function. We find that among all tested invertebrate CLIC proteins, function appears to be completely conserved despite striking differences in the charged residues contained within the amphipathic helix. This indicates that these residues do not contribute to anion selectivity as previously suggested. We find that outside the PTM region, the remaining three-quarters of CLIC protein sequence is functionally equivalent not only among vertebrate and invertebrate CLIC proteins, but also among the more distantly related GST-omega and GST-sigma proteins. The PTM region thus provides both targeting information and CLIC functional specificity, possibly adapting GST-type proteins to function as ion channels.

Amino Acid Sequence↗
PubMed2006

Oliver Hobert.

Explore the source record for details and available documents.

Animals↗
PubMed2006

Developmental regulation of whole cell capacitance and membrane current in identified interneurons in C. elegans.

Postembryonic developmental changes in electrophysiological properties of the AIY interneuron class were investigated using whole cell voltage clamp. AIY interneurons displayed an increase in cell capacitance during larval development, whereas steady-state current amplitude did not increase. The time course of the outward membrane current, carried at least in part by K+ ions, matured, from a slowly activating, sustained current to a rapidly activating, decaying current. We also investigated how the development of capacitance and outward current was altered by loss-of-function mutations in genes expressed in AIY. One such gene, the LIM homeobox gene ttx-3, is known to be involved in the specification of the AIY neuronal subtype. In ttx-3 mutants, capacitance and outward current matured precociously. In mutants of the gene wrk-1, an immunoglobulin superfamily (IgSF) member whose expression is regulated by ttx-3, capacitance matured normally, whereas outward current matured precociously. We conclude that AIY interneurons contain distinct pathways for regulating capacitance and membrane current.

Aging↗
PubMed2006

Searching for neuronal left/right asymmetry: genomewide analysis of nematode receptor-type guanylyl cyclases.

Functional left/right asymmetry ("laterality") is a fundamental feature of many nervous systems, but only very few molecular correlates to functional laterality are known. At least two classes of chemosensory neurons in the nematode Caenorhabditis elegans are functionally lateralized. The gustatory neurons ASE left (ASEL) and ASE right (ASER) are two bilaterally symmetric neurons that sense distinct chemosensory cues and express a distinct set of four known chemoreceptors of the guanylyl cyclase (gcy) gene family. To examine the extent of lateralization of gcy gene expression patterns in the ASE neurons, we have undertaken a genomewide analysis of all gcy genes. We report the existence of a total of 27 gcy genes encoding receptor-type guanylyl cyclases and of 7 gcy genes encoding soluble guanylyl cyclases in the complete genome sequence of C. elegans. We describe the expression pattern of all previously uncharacterized receptor-type guanylyl cyclases and find them to be highly biased but not exclusively restricted to the nervous system. We find that >41% (11/27) of all receptor-type guanylyl cyclases are expressed in the ASE gustatory neurons and that one-third of all gcy genes (9/27) are expressed in a lateral, left/right asymmetric manner in the ASE neurons. The expression of all laterally expressed gcy genes is under the control of a gene regulatory network composed of several transcription factors and miRNAs. The complement of gcy genes in the related nematode C. briggsae differs from C. elegans as evidenced by differences in chromosomal localization, number of gcy genes, and expression patterns. Differences in gcy expression patterns in the ASE neurons of C. briggsae arise from a difference in cis-regulatory elements and trans-acting factors that control ASE laterality. In sum, our results indicate the existence of a surprising multitude of putative chemoreceptors in the gustatory ASE neurons and suggest the existence of a substantial degree of laterality in gustatory signaling mechanisms in nematodes.

Alleles↗
PubMed2006

The molecular diversity of glycosaminoglycans shapes animal development.

Proteoglycans (PGs), molecules in which glycosaminoglycans (GAGs) are covalently linked to a protein core, are components of the extracellular matrix of all multicellular organisms. Sugar moieties in GAGs are often extensively modified, which make these molecules enormously complex. We discuss here the role of PGs during animal development, emphasizing the in vivo significance of sugar modifications. We explore a model in which the modification patterns of GAG chains may provide a specific code that contributes to the correct development of a multicellular organism.

Animals↗
PubMed2005

A novel C. elegans zinc finger transcription factor, lsy-2, required for the cell type-specific expression of the lsy-6 microRNA.

The two Caenorhabditis elegans gustatory neurons, ASE left (ASEL) and ASE right (ASER) are morphologically bilaterally symmetric, yet left/right asymmetric in function and in the expression of specific chemosensory signaling molecules. The ASEL versus ASER cell-fate decision is controlled by a complex gene regulatory network composed of microRNAs (miRNAs) and transcription factors. Alterations in the activities of each of these regulatory factors cause a complete lateral cell-fate switch. Here, we describe lsy-2, a novel C2H2 zinc finger transcription factor that is required for the execution of the ASEL stable state. In lsy-2 null mutants, the ASEL neuron adopts the complete ASER gene expression profile, including both upstream regulatory and terminal effector genes. The normally left/right asymmetric ASE neurons are therefore ;symmetrized' in lsy-2 mutants. Cell-specific rescue experiments indicate that lsy-2 is required autonomously in ASEL for the activation of ASEL-specifying factors and the repression of ASER-specifying factors. Genetic epistasis experiments demonstrate that lsy-2 exerts its activity by regulating the transcription of the lsy-6 miRNA in the ASEL neuron, thereby making lsy-2 one of the few factors known to control the cell-type specificity of miRNA gene expression.

Amino Acid Sequence↗
PubMed2005

MicroRNAs acting in a double-negative feedback loop to control a neuronal cell fate decision.

The elucidation of the architecture of gene regulatory networks that control cell-type specific gene expression programs represents a major challenge in developmental biology. We describe here a cell fate decision between two alternative neuronal fates and the architecture of a gene regulatory network that controls this cell fate decision. The two Caenorhabditis elegans taste receptor neurons "ASE left" (ASEL) and "ASE right" (ASER) share many bilaterally symmetric features, but each cell expresses a distinct set of chemoreceptors that endow the gustatory system with the capacity to sense and discriminate specific environmental inputs. We show that these left/right asymmetric fates develop from a precursor state in which both ASE neurons express equivalent features. This hybrid precursor state is unstable and transitions into the stable ASEL or ASER terminal end state. Although this transition is spatially stereotyped in wild-type animals, mutant analysis reveals that each cell has the potential to transition into either the ASEL or ASER stable end state. The stability and irreversibility of the terminal differentiated state is ensured by the interactions of two microRNAs (miRNAs) and their transcription factor targets in a double-negative feedback loop. Simple feedback loops are found as common motifs in many gene regulatory networks, but the loop described here is unusually complex and involves miRNAs. The interaction of miRNAs in double-negative feedback loops may not only be a means for miRNAs to regulate their own expression but may also represent a general paradigm for how terminal cell fates are selected and stabilized.

Animals↗
PubMed2005

An interneuronal chemoreceptor required for olfactory imprinting in C. elegans.

Animals alter their behavioral patterns in an experience-dependent manner. Olfactory imprinting is a process in which the exposure of animals to olfactory cues during specific and restricted time windows leaves a permanent memory ("olfactory imprint") that shapes the animal's behavior upon encountering the olfactory cues at later times. We found that Caenorhabditis elegans displays olfactory imprinting behavior that is mediated by a single pair of interneurons. To function in olfactory imprinting, this interneuron pair must express a G protein-coupled chemoreceptor family member encoded by the sra-11 gene. Our study provides insights into the cellular and molecular basis of olfactory imprinting and reveals a function for a chemosensory receptor family member in interneurons.

Animals↗
PubMed2005

MicroRNAs: all gone and then what?

MicroRNAs are abundant gene regulatory factors whose function in animal development and homeostasis is poorly understood. A new study reports the genetic elimination of miRNA function on a full genomic scale and identifies a subfamily of miRNAs involved in brain morphogenesis.

Animals↗
PubMed2004

MicroRNAs act sequentially and asymmetrically to control chemosensory laterality in the nematode.

Animal microRNAs (miRNAs) are gene regulatory factors that prevent the expression of specific messenger RNA targets by binding to their 3' untranslated region. The Caenorhabditis elegans lsy-6 miRNA (for lateral symmetry defective) is required for the left/right asymmetric expression of guanyl cyclase (gcy) genes in two chemosensory neurons termed ASE left (ASEL) and ASE right (ASER). The asymmetric expression of these putative chemoreceptors in turn correlates with the functional lateralization of the ASE neurons. Here we find that a mutation in the die-1 zinc-finger transcription factor disrupts both the chemosensory laterality and left/right asymmetric expression of chemoreceptor genes in the ASE neurons. die-1 controls chemosensory laterality by activating the expression of lsy-6 specifically in ASEL, but not in ASER, where die-1 expression is downregulated through two sites in its 3' untranslated region. These two sites are complementary to mir-273, a previously uncharacterized miRNA, whose expression is strongly biased towards ASER. Forced bilateral expression of mir-273 in ASEL and ASER causes a loss of asymmetric die-1 expression and ASE laterality. Thus, an inverse distribution of two sequentially acting miRNAs in two bilaterally symmetric neurons controls laterality of the nematode chemosensory system.

Animals↗
PubMed2004

Caenorhabditis elegans ABL-1 antagonizes p53-mediated germline apoptosis after ionizing irradiation.

c-Abl, a conserved nonreceptor tyrosine kinase, integrates genotoxic stress responses, acting as a transducer of both pro- and antiapoptotic effector pathways. Nuclear c-Abl seems to interact with the p53 homolog p73 to elicit apoptosis. Although several observations suggest that cytoplasmic localization of c-Abl is required for antiapoptotic function, the signals that mediate its antiapoptotic effect are largely unknown. Here we show that worms carrying an abl-1 deletion allele, abl-1(ok171), are specifically hypersensitive to radiation-induced apoptosis in the Caenorhabditis elegans germ line. Our findings delineate an apoptotic pathway antagonized by ABL-1, which requires sequentially the cell cycle checkpoint genes clk-2, hus-1 and mrt-2; the C. elegans p53 homolog, cep-1; and the genes encoding the components of the conserved apoptotic machinery, ced-3, ced-9 and egl-1. ABL-1 does not antagonize germline apoptosis induced by the DNA-alkylating agent ethylnitrosourea. Furthermore, worms treated with the c-Abl inhibitor STI-571 (Gleevec; used in human cancer therapy), two newly synthesized STI-571 variants or PD166326 had a phenotype similar to that generated by abl-1(ok171). These studies indicate that ABL-1 distinguishes proapoptotic signals triggered by two different DNA-damaging agents and suggest that C. elegans might provide tissue models for development of anticancer drugs.

Amino Acid Sequence↗