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J Kimble

Publications and source records attributed to J Kimble.

At least 55 records · Page 3Linked to original sources
PubMed1995

A predicted membrane protein, TRA-2A, directs hermaphrodite development in Caenorhabditis elegans.

The nematode C. elegans naturally develops as either an XO male or XX hermaphrodite. The sex-determining gene, tra-2, promotes hermaphrodite development in XX animals. This gene encodes a predicted membrane protein, named TRA-2A, which has been proposed to provide the primary feminising activity of the tra-2 locus. Here, we show that transgenic TRA-2A driven from a heat shock promoter can fully feminise the somatic tissues of XX tra-2 loss-of-function mutants, which would otherwise develop as male. TRA-2A is thus likely to provide a component of the tra-2 locus that is both necessary and sufficient to promote female somatic development. Transgenic TRA-2A driven by the heat shock promoter can also transform XO animals from male to self-fertile hermaphrodite. This result establishes the role of tra-2 as a developmental switch that controls somatic sexual cell fate. We show that a carboxy-terminal region of TRA-2A, predicted to be intra-cellular, can partially feminise XX tra-2 loss-of-function mutants and XO tra-2(+) males. We suggest that this intra-cellular domain of TRA-2A promotes hermaphrodite development by negatively regulating the FEM proteins.

Animals↗
PubMed1994

Translational control of maternal glp-1 mRNA establishes an asymmetry in the C. elegans embryo.

In C. elegans, the glp-1 gene encodes a membrane receptor that is required for anterior cell fates in the early embryo. We report that GLP-1 protein is localized to anterior blastomeres in 2- to 28-cell embryos. By contrast, glp-1 mRNA is present in all blastomeres until the 8-cell stage. Furthermore, the glp-1 3' untranslated region can restrict translation of a reporter mRNA to anterior blastomeres. Therefore, the translation of maternal glp-1 mRNA is temporally and spatially regulated in the C. elegans embryo. The regulation of maternal glp-1 mRNA has striking parallels to the regulation of maternal hunchback mRNA in the Drosophila embryo. Thus, the establishment of embryonic asymmetry in diverse organisms may involve conserved mechanisms of maternal mRNA regulation.

Animals↗
PubMed1994

Control of germ cell differentiation in Caenorhabditis elegans.

The germline of Caenorhabditis elegans is organized in a linear fashion--the most distal germ cells remain in mitosis, those in the middle enter meiosis and proximal cells differentiate as sperm or oocytes. Two signal transduction pathways control germ cell fates. The glp-1 gene mediates a signal that promotes mitosis and the genes of the sex determination pathway mediate a signal that determines if germ cells will develop as sperm or oocytes. Information from these pathways acts through terminal regulators to specify cell fate. For example, fog-1 and fog-3 are required to initiate spermatogenesis and gld-1 appears to be required to initiate oogenesis. Study of these terminal regulators suggests that the decisions about sexual identity and mitosis are linked in germ cells. We propose a tripartite interaction that forces germ cells to adopt one of only three fates--mitosis, spermatogenesis or oogenesis.

Animals↗
PubMed1994

GLP-1 is localized to the mitotic region of the C. elegans germ line.

In C. elegans, germline mitosis depends on induction by the somatic distal tip cell (DTC) and on activity of the glp-1 gene. Using antibodies to GLP-1 protein, we have examined GLP-1 on western blots and by immunocytochemistry. GLP-1 is tightly associated with membranes of mitotic germline cells, supporting its identification as an integral membrane protein. Furthermore, GLP-1 is localized within the germ line to the mitotic region, consistent with the model that GLP-1 acts as a membrane receptor for the distal tip cell signal. Unexpectedly, GLP-1 and the zone of mitosis extend further than the DTC processes. We present three models by which the DTC may influence GLP-1 activity and thereby determine the zone of mitosis. The spatial restriction of GLP-1 appears to be controlled at the translational level in hermaphrodites. We suggest that down-regulation of GLP-1 may be required to effect the transition from mitosis into meiosis.

Animals↗
PubMed1994

lag-2 may encode a signaling ligand for the GLP-1 and LIN-12 receptors of C. elegans.

The C. elegans lag-2 gene is required for several cell-cell interactions that rely on the receptors GLP-1 and LIN-12. In this paper, we report that lag-2 encodes a putative membrane protein with sequence similarity to Drosophila Delta, a proposed ligand for the Notch receptor. Furthermore, we show that the lag-2 promoter drives expression of a reporter protein in the signaling distal tip cell (DTC) of the DTC/germline interaction. By in situ hybridization, we have found that endogenous lag-2 mRNA is present in the DTC but not the germ line. One fusion protein, called LAG-2::beta-gal(intra), rescues a lag-2 null mutant and can be detected in both DTC and germ line. Taking these results together, we propose that lag-2 may encode a signaling ligand for GLP-1/LIN-12 and that the entire LAG-2 protein may be taken up into the receiving cell during induction by GLP-1 and lateral signaling by LIN-12.

Amino Acid Sequence↗
PubMed1994

The pha-4 gene is required to generate the pharyngeal primordium of Caenorhabditis elegans.

In the 4-cell Caenorhabditis elegans embryo, two blastomeres are destined to generate pharyngeal cells, each by a distinct developmental strategy: one pathway is inductive, while the other is autonomous. Here, we identify the pha-4 locus. In animals lacking pha-4 activity, an early step in pharyngeal organogenesis is blocked: no pharyngeal primordium is formed and differentiated pharyngeal cells are absent. Most other tissues are generated normally in pha-4 mutants, including cells related to pharyngeal cells by cell lineage and position. Thus, pha-4 activity is required to form the pharyngeal primordium. We propose that pha-4 marks a convergence of the inductive and autonomous pathways of pharyngeal development and suggest that establishment of pharyngeal organ identity is a crucial step for pharyngeal organogenesis.

Animals↗
PubMed1993

Translational regulation of tra-2 by its 3' untranslated region controls sexual identity in C. elegans.

C. elegans hermaphrodites make sperm and then oocytes in an otherwise female animal. Gain-of-function mutations in the sex-determining gene tra-2 (tra-2(gf)) transform hermaphrodites into females (spermless hermaphrodites). The tra-2(gf) mutations map to a perfect direct repeat in the 3' untranslated region; each repeat is called a direct repeat element (DRE). Three experiments demonstrate that DREs repress tra-2 at the translational level. First, tra-2(gf) mRNAs are associated with larger polysomes than are their wild-type counterparts. Second, translation of a reporter RNA is inhibited by DREs. Third, disruption of DREs does not increase tra-2 mRNA levels. An RNA binding activity specifically associates with the DREs. We propose that tra-2 translation is inhibited by association of an RNA binding-factor with the DREs and that this translational control is essential for development of C. elegans as a hermaphrodite/male species.

Animals↗
PubMed1993

Control of cell fate in C. elegans by a GLP-1 peptide consisting primarily of ankyrin repeats.

The homologous proteins GLP-1 and LIN-12 are required for cell interactions during nematode development. glp-1 and lin-12 are members of a gene family that includes Drosophila Notch and several vertebrate homologues. The members of this family have a single transmembrane domain and a similar arrangement of repeated amino-acid motifs (see Fig. 1). The mechanism by which proteins in this family function is not understood. One hypothesis is that these proteins are receptors, each with an extracellular domain that binds a ligand and an intracellular domain that influences the activity of downstream cell fate regulators. Here we report that a region of the GLP-1 intracellular domain, consisting primarily of six ankyrin repeats, is sufficient to direct cell fate. The cell fate transformations seen are similar to transformations caused by gain-of-function mutations in either glp-1 or lin-12 and do not rely on endogenous lin-12 or glp-1 activity. We propose that the ankyrin repeat region of GLP-1 is responsible for controlling downstream regulators of cell fate.

Amino Acid Sequence↗
PubMed1993

More mog genes that influence the switch from spermatogenesis to oogenesis in the hermaphrodite germ line of Caenorhabditis elegans.

The Caenorhabditis elegans XX animal possesses a hermaphrodite germ line, producing first sperm, then oocytes. In this paper, we report the genetic identification of five genes, mog-2, mog-3, mog-4, mog-5, and mog-6, that influence the hermaphrodite switch from spermatogenesis to oogenesis. In mog-2-mog-6 mutants, spermatogenesis continues past the time at which hermaphrodites normally switch into oogenesis and no oocytes are observed. Therefore, in these mutants, germ cells are transformed from a female fate (oocyte) to a male fate (sperm). The fem-3 gene is one of five genes that acts at the end of the germline sex determination pathway to direct spermatogenesis. Analyses of mog;fem-3 double mutants suggest that the mog-2-mog-6 genes act before fem-3; thus these genes may be in a position to negatively regulate fem-3 or one of the other terminal regulators of germline sex determination. Double mutants of fem-3 and any one of the mog mutations make oocytes. Using these double mutants, we show that oocytes from any mog;fem-3 double mutant are defective in their ability to support embryogenesis. This maternal effect lethality indicates that each of the mog genes is required for embryogenesis. The two defects in mog-2-mog-6 mutants are similar to those of mog-1: all six mog genes eliminate the sperm/oocyte switch in hermaphrodites and cause maternal effect lethality. We propose that the mog-2-mog-6 mutations identify genes that act with mog-1 to effect the sperm/oocyte switch. We further speculate that the mog-1-mog-6 mutations all interfere with translational controls of fem-3 and other maternal mRNAs.

Alleles↗
PubMed1993

The mog-1 gene is required for the switch from spermatogenesis to oogenesis in Caenorhabditis elegans.

Caenorhabditis elegans hermaphrodites make first sperm, then oocytes. By contrast, animals homozygous for any of six loss-of-function mutations in the gene mog-1 (for masculinization of the germ line) make sperm continuously and do not switch into oogenesis. Therefore, in mog-1 mutants, germ cells that normally would become oocytes are transformed into sperm. By contrast, somatic sexual fates are normal, suggesting that mog-1 plays a germ line-specific role in sex determination. Analyses of double mutants suggest that mog-1 negatively regulates the fem genes and/or fog-1: mog-1; fem and mog-1; fog-1 double mutants all make oocytes rather than sperm. Therefore, we propose that wild-type mog-1 is required in the hermaphrodite germ line for regulation of the switch from spermatogenesis to oogenesis rather than for specification of oogenesis per se. In addition to its role in germline sex determination, maternal mog-1 is required for embryogenesis: most progeny of a mog-1; fem or mog-1; fog-1 mother die as embryos. How might the roles of mog-1 in the sperm/oocyte switch and embryogenesis be linked? Previous work showed that fem-3 is regulated post-transcriptionally to achieve the sperm/oocyte switch. We speculate that mog-1 may function in the post-transcriptional regulation of numerous germ-line RNAs, including fem-3. A loss of mog-1 might inappropriately activate fem-3 and thereby abolish the sperm/oocyte switch; its loss might also lead to misregulation of maternal RNAs and thus embryonic death.

Animals↗
PubMed1993

Suppressors of glp-1, a gene required for cell communication during development in Caenorhabditis elegans, define a set of interacting genes.

The glp-1 gene is essential for two cell interactions that control cell fate in Caenorhabditis elegans: induction of anterior pharynx in the embryo and induction of mitotic proliferation in the germ line. To identify other genes involved in these cell interactions, we have isolated suppressors of two temperature sensitive alleles of glp-1. Each of 14 recessive suppressors rescues both embryonic and germline glp-1(ts) defects. These suppressors are extragenic and define a set of six genes designated sog, for suppressor of glp-1. Suppression of glp-1 is the only obvious phenotype associated with sog mutations. Mutations in different sog genes show allele-specific intergenic noncomplementation, suggesting that the sog gene products may interact. In addition, we have analyzed a semidominant mutation that suppresses only the glp-1 germline phenotype and has a conditional feminized phenotype of its own. None of the suppressors rescues a glp-1 null mutation and therefore they do not bypass a requirement for glp-1. Distal tip cell function remains necessary for germline proliferation in suppressed animals. These suppressor mutations identify genes that may encode other components of the glp-1 mediated cell-signaling pathway or regulate glp-1 expression.

Alleles↗
PubMed1992

The Caenorhabditis elegans sex determining gene fem-3 is regulated post-transcriptionally.

The fem-3 gene of Caenorhabditis elegans is required for male development. Both maternal and zygotic fem-3 activities are required for spermatogenesis in the XX hermaphrodite germline and for male development in somatic and germline tissues XO (male) animals. Here we show that fem-3 RNA is contributed to embryos as a maternal product and that this RNA is degraded early in embryonic development. The poly(A) tail of embryonic fem-3 RNA is substantially longer than that of adult hermaphrodites which indicates that poly(A) tail lengthening probably occurs at or soon after fertilization. During subsequent development, fem-3 poly(A) tails shorten. The amount of fem-3 RNA in XX and XO embryos is equivalent, suggesting sex-specific regulation of maternal fem-3 activity occurs post-transcriptionally. The sequence of fem-3 predicts an open reading frame that could encode a soluble protein; putative fem-3 null mutants truncate this open reading frame. We discuss the implications of these results for the regulation and function of fem-3.

Amino Acid Sequence↗
PubMed1992

Molecular genetics of sex determination in C. elegans.

Sexual fate in the nematode Caenorhabditis elegans is controlled by a group of genetically well-characterized genes. Several of these sex-determining genes have now been analysed at the molecular level. Transcriptional regulation is likely to control both commitment to a single sexual fate and maintenance of that decision; in addition, intercellular signalling appears to coordinate the sexual fates of cells throughout the animal to adopt a single sexual fate.

Animals↗
PubMed1992

Molecular basis of loss-of-function mutations in the glp-1 gene of Caenorhabditis elegans.

The glp-1 gene encodes a membrane protein required for inductive cell interactions during development of the nematode Caenorhabditis elegans. Here we report the molecular characterization of 15 loss-of-function (lf) mutations of glp-1. Two nonsense mutations appear to eliminate glp-1 activity; both truncate the glp-1 protein in its extracellular domain and have a strong loss-of-function phenotype. Twelve missense mutations and one in-frame deletion map to sites within the repeated motifs of the glp-1 protein (10 epidermal growth factor [EGF]-like and 3 LNG repeats extracellularly and 6 cdc10/SWI6, or ankyrin, repeats intracellularly). We find that all three types of repeated motifs are critical to glp-1 function, and two individual EGF-like repeats may have distinct functions. Intriguingly, all four missense mutations in one phenotypic class map to the N-terminal EGF-like repeats and all six missense mutations in a second phenotypic class reside in the intracellular cdc10/SWI6 repeats. These two clusters of mutations may identify functional domains within the glp-1 protein.

Amino Acid Sequence↗
PubMed1992

tra-2 encodes a membrane protein and may mediate cell communication in the Caenorhabditis elegans sex determination pathway.

The Caenorhabditis elegans sex-determining gene, tra-2, promotes female development in XX animals. In this paper we report the cDNA sequence corresponding to a 4.7 kb tra-2 mRNA and show that it is composed of 23 exons, is trans-spliced to SL2, and contains a perfect direct repeat in the 3' untranslated region. This mRNA is predicted to encode a 1475 amino acid protein, named pTra2A, that has a secretory signal and several potential membrane-spanning domains. The molecular analysis of tra-2 loss-of-function mutations supports our open reading frame identification and suggests that the carboxy-terminal domain is important for tra-2 activity. We propose that in XX animals the carboxy-terminal domain of pTra2A negatively regulates the downstream male promoting fem genes. In XO animals, tra-2 is negatively regulated by her-1, which acts cell nonautonomously. Because hydropathy predictions suggest that pTra2A is an integral membrane protein, pTra2A might act as a receptor for the her-1 protein. We propose that in XO animals, the her-1 protein promotes male development by binding and inactivating pTra2A. The role of cell communication in C. elegans sex determination might be to ensure unified sexual development throughout the animal. If so, then regulation of sexual fate by her-1 and tra-2 might provide a general model for the coordination of groups of cells to follow a single cell fate.

Amino Acid Sequence↗
PubMed1991

Carboxy-terminal truncation activates glp-1 protein to specify vulval fates in Caenorhabditis elegans.

The glp-1 and lin-12 genes encode homologous transmembrane proteins that may act as receptors for cell interactions during development. The glp-1 product is required for induction of germ-line proliferation and for embryogenesis. By contrast, lin-12 mediates somatic cell interactions, including those between the precursor cells that form the vulval hypodermis (VPCs). Here we analyse an unusual allele of glp-1, glp-1(q35), which displays a semidominant multivulva phenotype (Muv), as well as the typical recessive, loss-of-function Glp phenotypes (sterility and embryonic lethality). We find that the effects of glp-1(q35) on VPC development mimic those of dominant lin-12 mutations, even in the absence of lin-12 activity. The glp-1(q35) gene bears a nonsense mutation predicted to eliminate the 122 C-terminal amino acids, including a ProGluSerThr (PEST) sequence thought to destabilize proteins. We suggest that the carboxy terminus bears a negative regulatory domain which normally inactivates glp-1 in the VPCs. We propose that inappropriate glp-1(q35) activity can substitute for lin-12 to determine vulval fate, perhaps by driving the VPCs to proliferate.

Amino Acid Sequence↗