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Biomedical subjects

J Kimble

Publications and source records attributed to J Kimble.

At least 19 recordsLinked to original sources
PubMed1999

The Caenorhabditis elegans sex determination gene mog-1 encodes a member of the DEAH-Box protein family.

In the Caenorhabditis elegans hermaphrodite germ line, the sex-determining gene fem-3 is repressed posttranscriptionally to arrest spermatogenesis and permit oogenesis. This repression requires a cis-acting regulatory element in the fem-3 3' untranslated region; the FBF protein, which binds to this element; and at least six mog genes. In this paper, we report the molecular characterization of mog-1 as well as additional phenotypic characterization of this gene. The mog-1 gene encodes a member of the DEAH-box family. Three mog-1 alleles possess premature stop codons and are likely to be null alleles, and one is a missense mutation and is likely to retain residual activity. mog-1 mRNA is expressed in both germ line and somatic tissues and appears to be ubiquitous. The MOG-1 DEAH-box protein is most closely related to proteins essential for splicing in the yeast Saccharomyces cerevisiae, but splicing appears to occur normally in a mog-1-null mutant. In addition to its involvement in the sperm-oocyte switch and control of fem-3, zygotic mog-1 is required for robust germ line proliferation and for normal growth during development. We suggest that mog-1 plays a broader role in RNA regulation than previously considered.

Amino Acid Sequence↗
PubMed1998

Germ-line regulation of the Caenorhabditis elegans sex-determining gene tra-2.

The Caenorhabditis elegans sex-determining gene tra-2 promotes female development of the XX hermaphrodite soma and germ line. We previously showed that a 4.7-kb tra-2 mRNA, which encodes the membrane protein TRA-2A, provides the primary feminizing activity of the tra-2 locus. This paper focuses on the germ-line activity and regulation of tra-2. First, we characterize a 1.8-kb tra-2 mRNA, which is hermaphrodite-specific and germ-line-dependent. This mRNA encodes TRA-2B, a protein identical to a predicted intracellular domain of TRA-2A. We show that the 1.8-kb mRNA is oocyte-specific, suggesting that it is involved in germ-line or embryonic sex determination. Second, we identify a tra-2 maternal effect on brood size that may be associated with the 1.8-kb mRNA. Third, we investigate seven dominant tra-2(mx) (for mixed character) mutations that sexually transform hermaphrodites to females by eliminating hermaphrodite spermatogenesis. Each of the tra-2(mx) mutants possesses a nonconserved missense change in a 22-amino-acid region common to both TRA-2A and TRA-2B, called the MX region. We propose that the MX region mediates a posttranslational regulation of tra-2 essential for the onset of hermaphrodite spermatogenesis. Finally, we discuss aspects of tra-2 function and regulation that are specific to the unusual control of cell fate in the hermaphrodite germ line.

Amino Acid Sequence↗
PubMed1998

Repression by the 3' UTR of fem-3, a sex-determining gene, relies on a ubiquitous mog-dependent control in Caenorhabditis elegans.

The fem-3 sex-determining gene is repressed post-transcriptionally via a regulatory element in its 3' untranslated region (UTR) to achieve the switch from spermatogenesis to oogenesis in the Caenorhabditis elegans hermaphrodite germ line. In this paper, we investigate the fem-3 3' UTR control in somatic tissues using transgenic reporter assays, and we also identify six genes essential for this control. First, we find that a reporter transgene bearing a wild-type fem-3 3' UTR is repressed in somatic tissues, whereas one bearing a mutant fem-3 3' UTR is derepressed. Moreover, control by mutant 3' UTRs is temperature sensitive as predicted from the temperature sensitivity of the fem-3 gain-of-function (gf) mutations. Secondly, we find a fem-3 3' UTR RNA-binding activity in somatic tissues, in addition to the previously reported germ-line-specific binding by FBF. Thirdly, we find that each of six genes, mog-1-mog-6, is required for repression by the fem-3 3' UTR. Therefore, the mog genes not only affect the sperm/oocyte switch in the germ line, but also function in somatic tissues. We suggest that the mog genes may encode components of a ubiquitous machinery that is used for fem-3 3' UTR-mediated repression and the sperm/oocyte switch.

3' Untranslated Regions↗
PubMed1998

pha-4, an HNF-3 homolog, specifies pharyngeal organ identity in Caenorhabditis elegans.

To build complex organs, embryos have evolved mechanisms that integrate the development of cells unrelated to one another by cell type or ancestry. Here we show that the pha-4 locus establishes organ identity for the Caenorhabditis elegans pharynx. In pha-4 mutants, pharyngeal cells are transformed into ectoderm. Conversely, ectopic pha-4 expression produces excess pharyngeal cells. pha-4 encodes an HNF-3 homolog selectively expressed in the nascent digestive tract, including all pharynx precursors at the time they are restricted to a pharyngeal fate. We suggest that pha-4 is a key component of a transcription-based mechanism to endow cells with pharyngeal organ identity.

Animals↗
PubMed1998

Notch/LIN-12 signaling: transduction by regulated protein slicing.

Intercellular signaling through the Notch/LIN-12 transmembrane receptors regulates growth and differentiation during animal development. Moreover, defects in the conserved Notch/LIN-12 pathway are linked to human diseases. Here, we review models for two key steps in Notch/LIN-12 signaling: ligand-mediated activation of the receptor and receptor-mediated activation of transcription. Ligand binding appears to permit proteolysis of the receptor; as a result, the receptor's intracellular domain can enter the nucleus and function as a transcriptional co-activator.

Animals↗
PubMed1998

Patient-controlled sedation and analgesia, using propofol and alfentanil, during colonoscopy: a prospective randomized controlled trial.

BACKGROUND AND STUDY AIMS: Patient-controlled sedation (PCS) enables titration of dosage to an individual's requirements and is potentially useful in colonoscopy. The aim was to compare the value of patient-controlled sedation, using propofol and alfentanil, with that of intravenous diazemuls and pethidine during colonoscopy. PATIENTS AND METHODS: Following randomization, 66 patients undergoing colonoscopy received either an intravenous bolus of pethidine (50 mg) and diazemuls (10-20 mg) prior to colonoscopy or were connected to an infusion pump containing propofol (10 mg/ml) and alfentanil (25 microg/ml). Patients self-administered 0.5 ml boluses as often as they required. Pain and sedation score were recorded by a nurse specialist and on a patient questionnaire. An anaesthetist was present throughout the procedure. RESULTS: PCS provided lighter sedation (median sedation score, 3 versus 4; P=0.0001), less analgesia (median pain score, 1 versus 0; P=0.004), a smaller maximum fall in systolic blood pressure (23 mmHg versus 33 mmHg; P=0.02) and a faster recovery time (median 10 min versus 40 min; P=0.0001), irrespective of the dose administered, compared with a diazemuls-pethidine combination. The duration of the procedure was unaffected. All patients were satisfied with their level of sedation. CONCLUSIONS: Patient-controlled sedation is an effective alternative to premedication with narcotic/benzodiazepine combinations during colonoscopy.

Adult↗
PubMed1998

Genetic regulation of entry into meiosis in Caenorhabditis elegans.

The Caenorhabditis elegans germline is composed of mitotically dividing cells at the distal end that give rise to meiotic cells more proximally. Specification of the distal region as mitotic relies on induction by the somatic distal tip cell and the glp-1 signal transduction pathway. However, the genetic control over the transition from mitosis to meiosis is not understood. In this paper, we report the identification of a gene, gld-2, that has at least two functions in germline development. First, gld-2 is required for normal progression through meiotic prophase. Second, gld-2 promotes entry into meiosis from the mitotic cell cycle. With respect to this second function, gld-2 appears to be functionally redundant with a previously described gene, gld-1 (Francis, R., Barton, M. K., Kimble, J. and Schedl, T. (1995) Genetics 139, 579-606). Germ cells in gld-1(o) and gld-2 single mutants enter meiosis at the normal time, but germ cells in gld-2 gld-1(o) double mutants do not enter meiosis. Instead, the double mutant germline is mitotic throughout and forms a large tumor. We suggest that gld-1 and gld-2 define two independent regulatory pathways, each of which can be sufficient for entry into meiosis. Epistasis analyses show that gld-1 and gld-2 work downstream of the glp-1 signal transduction pathway. Therefore, we hypothesize that glp-1 promotes proliferation by inhibiting the meiosis-promoting functions of gld-1 and gld-2.

Animals↗
PubMed1998

Metal stents improve dysphagia, nutrition and survival in malignant oesophageal stenosis: a randomized controlled trial comparing modified Gianturco Z-stents with plastic Atkinson tubes.

OBJECTIVE: To compare modified Gianturco metal stents with plastic Atkinson tubes in the palliation of malignant dysphagia. DESIGN: Patient single-blind, multi-centre prospective, randomized trial. SETTING: Three district general hospitals in the Wessex region. PARTICIPANTS: Thirty one consecutive patients with inoperable malignant oesophageal stenosis causing dysphagia and suitable for treatment with an endoprosthesis. INTERVENTIONS: Patients were randomized to receive either a modified Gianturco metal stent or a plastic Atkinson tube. Sedation was similar and patients were given identical dietary advice. Data were collected after insertion until the patients' death. MAIN OUTCOME MEASURES: Procedural mortality/morbidity; hospital stay; weight loss; quality of life (Nottingham Health Profile, Spitzer QL index and specific questions about dysphagia and enjoyment of food); duration of survival after insertion; cost effectiveness of each intervention. RESULTS: Overall complication rates were similar in the two groups. Compared with Atkinson tubes, patients with Gianturco stents had better palliation of dysphagia (median dysphagia score 1 vs 2, P = 0.04), maintained their weight longer (median percent weight loss 0.66 vs 6.51, P = 0.007), enjoyed food more (enjoyment score 2 vs 1, P = 0.03) and survived longer (log rank P < 0.025). Patients with metal stents were discharged from hospital earlier (Gianturco 4 days, Atkinson 10 days, P = 0.001), and initial treatment cost was lower if the cost of hospital stay exceeded pound sterling 120 per day. CONCLUSION: Gianturco stents are superior to Atkinson tubes in the palliation of malignant oesophageal stenosis.

Deglutition Disorders↗
PubMed1997

A conserved RNA-binding protein that regulates sexual fates in the C. elegans hermaphrodite germ line.

The nematode Caenorhabditis elegans has two sexes, males and hermaphrodites. Hermaphrodites Initially produce sperm but switch to producing oocytes. This switch appears to be controlled by the 3' untranslated region of fem-3 messenger RNA. We have now identified a binding factor (FBF) which is a cytoplasmic protein that binds specifically to the regulatory region of fem-3 3'UTR and mediates the sperm/oocyte switch. The RNA-binding domain of FBF consists of a stretch of eight tandem repeats and two short flanking regions. This structural element is conserved in several proteins including Drosophila Pumilio, a regulatory protein that controls pattern formation in the fly by binding to a 3'UTR. We propose that FBF and Pumilio are members of a widespread family of sequence-specific RNA-binding proteins.

Amino Acid Sequence↗
PubMed1997

The origin and evolution of animal appendages.

Animals have evolved diverse appendages adapted for locomotion, feeding and other functions. The genetics underlying appendage formation are best understood in insects and vertebrates. The expression of the Distal-less (Dll) homeoprotein during arthropod limb outgrowth and of Dll orthologs (Dlx) in fish fin and tetrapod limb buds led us to examine whether expression of this regulatory gene may be a general feature of appendage formation in protostomes and deuterostomes. We find that Dll is expressed along the proximodistal axis of developing polychaete annelid parapodia, onychophoran lobopodia, ascidian ampullae, and even echinoderm tube feet. Dll/Dlx expression in such diverse appendages in these six coelomate phyla could be convergent, but this would have required the independent co-option of Dll/Dlx several times in evolution. It appears more likely that ectodermal Dll/Dlx expression along proximodistal axes originated once in a common ancestor and has been used subsequently to pattern body wall outgrowths in a variety of organisms. We suggest that this pre-Cambrian ancestor of most protostomes and the deuterostomes possessed elements of the genetic machinery for and may have even borne appendages.

Amino Acid Sequence↗
PubMed1997

Genes required for GLP-1 asymmetry in the early Caenorhabditis elegans embryo.

The translation of maternal glp-1 mRNA is regulated both temporally and spatially in the early Caenorhabditis elegans embryo (T. C. Evans, S. L. Crittenden, V. Kodoyianni, and J. Kimble, Cell 77, 183-194, 1994). To investigate the control of embryonic glp-1 expression, we have examined the distribution of GLP-1 protein in selected maternal effect mutants that affect pattern or fate in the early embryo. We find that mutants that disrupt anterior-posterior asymmetry in the early embryo (par-1-par-6, emb-8, Par(q537)) disrupt the spatial but not temporal control of GLP-1 expression: GLP-1 is observed at the normal stage of embryogenesis in par-like mutants; however, it is uniformly distributed. In contrast, mutants that alter blastomere identity (skn-1, pie-1, mex-1, apx-1) do not affect the normal GLP-1 pattern. We conclude that genes controlling the asymmetry of cellular components, including P granules, also control GLP-1 asymmetry in the early embryo. The finding that mutants that disrupt anterior-posterior asymmetry translate GLP-1 in all blastomeres suggests that loss of embryonic asymmetry causes translational activation of GLP-1 in the posterior.

Animals↗
PubMed1997

Functional domains of LAG-2, a putative signaling ligand for LIN-12 and GLP-1 receptors in Caenorhabditis elegans.

The LAG-2 membrane protein is a putative signaling ligand for the LIN-12 and GLP-1 receptors of Caenorhabditis elegans. LAG-2, like its Drosophila homologues Delta and Serrate, acts in a conserved signal transduction pathway to regulate cell fates during development. In this article, we investigate the functional domains of LAG-2. For the most part, mutants were constructed in vitro and assayed for activity in transgenic animals. We find a functional role for all major regions except one. Within the extracellular domain, the N-terminal region, which bears no known motif, and the DSL domain are both required. By contrast, the region bearing epidermal growth factor-like repeats can be deleted with no apparent reduction in rescuing activity. The intracellular region is not required for activity but instead plays a role in down-regulating LAG-2 function. Finally, membrane association is critical for mutant rescue.

Animals↗
PubMed1997

glp-3 is required for mitosis and meiosis in the Caenorhabditis elegans germ line.

The germ line is the only tissue in Caenorhabditis elegans in which a stem cell population continues to divide mitotically throughout life; hence the cell cycles of the germ line and the soma are regulated differently. Here we report the genetic and phenotypic characterization of the glp-3 gene. In animals homozygous for each of five recessive loss-of-function alleles, germ cells in both hermaphrodites and males fail to progress through mitosis and meiosis, but somatic cells appear to divide normally. Germ cells in animals grown at 15 degrees appear by DAP1 staining to be uniformly arrested at the G2/M transition with < 20 germ cells per gonad on average, suggesting a checkpoint-mediated arrest. In contrast, germ cells in mutant animals grown at 25 degrees frequently proliferate slowly during adulthood, eventually forming small germ lines with several hundred germ cells. Nevertheless, cells in these small germ lines never undergo meiosis. Double mutant analysis with mutations in other genes affecting germ cell proliferation supports the idea that glp-3 may encode a gene product that is required for the mitotic and meiotic cell cycles in the C. elegans germ line.

Animals↗
PubMed1997

The LIN-12/Notch signaling pathway and its regulation.

Notch, LIN-12, and GLP-1 are receptors that mediate a broad range of cell interactions during Drosophila and nematode development. Signaling by these receptors relies on a conserved pathway with three core components: DSL ligand, LNG receptor, and a CSL effector that links the receptor to its transcriptional response. Although key functional regions have been identified in each class of proteins, the mechanism for signal transduction is not yet understood. Diverse regulatory mechanisms influence signaling by the LIN-12/Notch pathway. Inductive signaling relies on the synthesis of ligand and receptor in distinct but neighboring cells. By contrast, lateral signaling leads to the transformation of equivalent cells that express both ligand and receptor into nonequivalent cells that express either ligand or receptor. This transformation appears to rely on regulatory feedback loops within the LIN-12/Notch pathway. In addition, the pathway can be regulated by intrinsic factors that are asymmetrically segregated during cell division or by extrinsic cues via other signaling pathways. Specificity in the pathway does not appear to reside in the particular ligand or receptor used for a given cell-cell interaction. The existence of multiple ligands and receptors may have evolved from the stringent demands placed upon the regulation of genes encoding them.

Animals↗
PubMed1997

A genetic pathway for regulation of tra-2 translation.

In Caenorhabditis elegans, the tra-2 sex-determining gene is regulated at the translational level by two 28 nt direct repeat elements (DREs) located in its 3' untranslated region (3'UTR). DRF is a factor that binds the DREs and may be a trans-acting translational regulator of tra-2. Here we identify two genes that are required for the normal pattern of translational control. A newly identified gene, called laf-1, is required for translational repression by the tra-2 3'UTR. In addition, the sex-determining gene, tra-3, appears to promote female development by freeing tra-2 from laf-1 repression. Finally, we show that DRF activity correlates with translational repression of tra-2 during development and that tra-3 regulates DRF activity. We suggest that tra-3 may promote female development by releasing tra-2 from translation repression by laf-1 and that translational control is important for proper sex determination--both in the early embryo and during postembryonic development.

Animals↗
PubMed1996

Roles of the RAM and ANK domains in signaling by the C. elegans GLP-1 receptor.

In Caenorhabditis elegans, the GLP-1 receptor acts with a downstream transcriptional regulator, LAG-1, to mediate intercellular signaling. GLP-1 and LAG-1 are homologs of Drosophila Notch and Su(H) respectively. Here, we investigate the functions of two regions of the GLP-1 intracellular domain: the ANK repeat domain, which includes six cdc10/ankyrin repeats plus flanking amino acids, and the RAM domain, which spans approximately 60 amino acids just inside the transmembrane domain. First, we demonstrate that both ANK and RAM domains interact with the LAG-1 transcription factor. The interaction between the ANK domain and LAG-1 is only observed in nematodes by a co-localization assay and, therefore, may be either direct or indirect. By contrast, the interaction between the RAM domain and LAG-1 is likely to be direct, since it is observed by co-precipitation of the proteins in vitro as well as by yeast two-hybrid experiments. Second, we demonstrate that the RAM domain, when expressed in nematodes without a functional ANK repeat domain, does not mimic the unregulated receptor in directing cell fates or interfere with signaling by endogenous components. Finally, we show in yeast that the ANK repeats are strong transcriptional activators. Furthermore, missense mutations that eliminate receptor activity also abolish transcriptional activation by the GLP-1 ANK repeats in yeast. We speculate that one possible function for the ANK repeat domain is to act as a transcriptional co-activator with LAG-1.

Amino Acid Sequence↗