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J Kimble

Publications and source records attributed to J Kimble.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1991

Control of the sperm-oocyte switch in Caenorhabditis elegans hermaphrodites by the fem-3 3' untranslated region.

In the Caenorhabditis elegans hermaphrodite germ line, sperm and then oocytes are made from a common pool of germ-cell precursors. The decision to differentiate as a sperm or an oocyte is regulated by the sex-determining gene, fem-3. Expression of fem-3 in the hermaphrodite germ line directs spermatogenesis and must be negatively regulated to allow the switch to oogenesis. In adult hermaphrodites (which are producing oocytes), most fem-3 RNA is found in the germ line, consistent with both the requirement for fem-3 in hermaphrodite spermatogenesis and the maternal effects of fem-3 on embryonic sex determination. Whereas loss-of-function mutants in fem-3 produce only oocytes, hermaphrodites carrying any of nine fem-3 gain-of-function (gf) mutations make none; instead sperm are produced continuously and in vast excess over wild-type amounts. Genetic analyses suggest that fem-3(gf) mutations have escaped a negative control required for the switch to oogenesis. Here we report that all nine fem-3(gf) mutants carry sequence alterations in the fem-3 3' untranslated region (3' UTR). There is no increase in the steady-state level of fem-3(gf) RNA over wild-type, but there is an increase in the polyadenylation of fem-3(gf) RNA that is coincident with the unregulated fem-3 activity. Results of a titration experiment support the hypothesis that a regulatory factor may bind the fem-3 3' UTR. We speculate that fem-3 RNA is regulated through its 3' UTR by binding a factor that inhibits translation, and discuss the idea that this control may be part of a more general regulation of maternal RNAs.

Animals↗
PubMed1991

Molecular analysis of tra-2, a sex determining gene in C.elegans.

We have cloned the Caenorhabditis elegans sex determining gene, tra-2, by transposon tagging. The tra-2 region is delineated by mapping Southern blot differences associated with 11 tra-2 mutations, mutant rescue, and analysis of tra-2 RNAs. The tra-2 gene encodes three transcripts. One transcript, a 1.8 kb RNA, is not detected in animals lacking a germ line, and therefore may be germline specific. Comparison of the two sexes shows that adult hermaphrodites have approximately 15-fold more tra-2 RNA than adult males. In addition, adult hermaphrodites contain 5 kb and 1.8 kb tra-2 RNAs whereas adult males possess 5 kb and 1.9 kb RNAs. A 1.9 kb tra-2 RNA is also found during hermaphrodite larval development, prior to sexual differentiation of the XX germ line. Surprisingly, analysis of tra-2 expression in selected sex determination mutants reveals that the sex specificity of tra-2 RNAs is not dictated by the pathway of sex determination that has been established by genetic experiments. This result can be interpreted in two ways. Either the sex specificity of the tra-2 RNAs is irrelevant to regulation of the sexual phenotype, which seems unlikely, or there is additional complexity within the hierarchy of sex determining genes, such as feedback regulation, which ensures that the tra-2 product corresponds to phenotypic sex.

Animals↗
PubMed1991

Two homologous regulatory genes, lin-12 and glp-1, have overlapping functions.

Two homologous genes, lin-12 and glp-1, encode transmembrane proteins required for regulatory cell interactions during C. elegans development. Based on their single mutant phenotypes, each gene has been thought to govern a distinct set of cell fates. We show here that lin-12 and glp-1 are functionally redundant during embryogenesis: Unlike either single mutant, the lin-12 glp-1 double mutant dies soon after hatching. Numerous cellular defects can be observed in these Lag (for lin-12 and glp-1) double mutants. Furthermore, we have identified two genes, lag-1 and lag-2, that appear to be required for both lin-12 and glp-1-mediated cell interactions. Strong loss-of-function lag mutants are phenotypically indistinguishable from the lin-12 glp-1 double; weak lag mutants have phenotypes typical of lin-12 and glp-1 single mutants. We speculate that the lin-12 and glp-1 proteins are biochemically interchangeable and that their divergent roles in development may rely largely on differences in gene expression.

Animals↗
PubMed1990

Genetic control of cell communication in C. elegans development.

Cell communication is crucial for many aspects of growth and differentiation during the development of the nematode Caenorhabditis elegans. Two genes, glp-1 and lin-12, mediate a number of known cell-cell interactions. Genetic and molecular analyses of these two genes lead to the conclusion that they are structurally and functionally related. We summarize these studies as well as those involving the identification of other genes that interact with glp-1 and/or lin-12.

Animals↗
PubMed1990

fog-1, a regulatory gene required for specification of spermatogenesis in the germ line of Caenorhabditis elegans.

In wild-type Caenorhabditis elegans, the XO male germ line makes only sperm and the XX hermaphrodite germ line makes sperm and then oocytes. In contrast, the germ line of either a male or a hermaphrodite carrying a mutation of the fog-1 (feminization of the germ line) locus is sexually transformed: cells that would normally make sperm differentiate as oocytes. However, the somatic tissues of fog-1 mutants remain unaffected. All fog-1 alleles identified confer the same phenotype. The fog-1 mutations appear to reduce fog-1 function, indicating that the wild-type fog-1 product is required for specification of a germ cell as a spermatocyte. Two lines of evidence indicate that a germ cell is determined for sex at about the same time that it enters meiosis. These include the fog-1 temperature sensitive period, which coincides in each sex with first entry into meiosis, and the phenotype of a fog-1; glp-1 double mutant. Experiments with double mutants show that fog-1 is epistatic to mutations in all other sex-determining genes tested. These results lead to the conclusion that fog-1 acts at the same level as the fem genes at the end of the sex determination pathway to specify germ cells as sperm.

Alleles↗
PubMed1989

Transcript analysis of glp-1 and lin-12, homologous genes required for cell interactions during development of C. elegans.

The glp-1 and lin-12 genes mediate several cell interactions during C. elegans development. We have identified the glp-1 gene in a region about 20 kb from lin-12. In collaboration with Yochem and Greenwald (1989; see accompanying paper), we show that a sequence identified by its similarity to lin-12 is in fact glp-1. We find a single 4.4 kb glp-1 transcript and a distinct 4.6 kb lin-12 transcript. Expression of the glp-1 transcript during development differs from that of lin-12. As expected from genetic analyses, glp-1 RNA is primarily in the germline while lin-12 RNA is primarily in the soma. Unexpectedly, we find that glp-1 RNA is also expressed in larval somatic tissues and that lin-12 RNA is abundant in early embryos. We suggest that glp-1 and lin-12 may play broader roles in development than previously thought.

Animals↗
PubMed1989

Genetic control of cellular interactions in Caenorhabditis elegans development.

During development of the nematode, Caenorhabditis elegans, cell interactions play a significant role in controlling cell fate. Regulatory cells in the somatic gonad control proliferation in the germline and induce formation of the vulva in the hypodermis. In the early embryo, mesodermal cells are induced in a process similar to embryonic induction. In addition, interactions between precursor cells of equivalent developmental potential direct one cell to adopt one fate and the other to adopt a second fate. Two genes have been identified in C. elegans that appear to mediate cell interactions. The glp-1 gene is required for embryonic induction and continued germline proliferation; lin-12 is required for cells of equal developmental potential to adopt different fates. Genetic mosaics indicate that glp-1 may be part of the receiving mechanism in controlling germline proliferation.

Animals↗
PubMed1989

Analysis of the role of tra-1 in germline sex determination in the nematode Caenorhabditis elegans.

In wild-type Caenorhabditis elegans there are two sexes, self-fertilizing hermaphrodites (XX) and males (XO). To investigate the role of tra-1 in controlling sex determination in germline tissue, we have examined germline phenotypes of nine tra-1 loss-of-function (lf) mutations. Previous work has shown that tra-1 is needed for female somatic development as the nongonadal soma of tra-1(lf) XX mutants is masculinized. In contrast, the germline of tra-1(lf) XX and XO animals is often feminized; a brief period of spermatogenesis is followed by oogenesis, rather than the continuous spermatogenesis observed in wild-type males. In addition, abnormal gonadal (germ line and somatic gonad) phenotypes are observed which may reflect defects in development or function of somatic gonad regulatory cells. Analysis of germline feminization and abnormal gonadal phenotypes of the various mutations alone or in trans to a deficiency reveals that they cannot be ordered in an allelic series and they do not converge to a single phenotypic endpoint. These observations lead to the suggestion that tra-1 may produce multiple products and/or is autoregulated. One interpretation of the germline feminization is that tra-1(+) is necessary for continued specification of spermatogenesis in males. We also report the isolation and characterization of tra-1 gain-of-function (gf) mutations with novel phenotypes. These include temperature sensitive, recessive germline feminization, and partial somatic loss-of-function phenotypes.

Alleles↗
PubMed1989

Identification of genes that interact with glp-1, a gene required for inductive cell interactions in Caenorhabditis elegans.

The glp-1 gene functions in two inductive cellular interactions and in development of the embryonic hypodermis of C. elegans. We have isolated six mutations as recessive suppressors of temperature-sensitive (ts) mutations of glp-1. By mapping and complementation tests, we found that these suppressors are mutations of known dumpy (dpy) genes; dpy genes are required for development of normal body shape. Based on this result, we asked whether mutations previously isolated in screens for mutants defective in body shape could also suppress glp-1(ts). From these tests, we learned that unselected mutations of eight genes required for normal C. elegans morphogenesis, including the four already identified, suppress glp-1(ts). All of these suppressors rescue all three mutant phenotypes of glp-1(ts) (defects in embryonic induction of pharyngeal tissue, in embryonic hypodermis development, and in induction of germline proliferation). However, they do not rescue putative glp-1 null mutants and therefore do not bypass the requirement for glp-1 in development. In the light of current ideas about the molecular nature of the glp-1 and suppressor gene products, we propose an interaction between the glp-1 protein and components of the extracellular matrix and speculate that this interaction may impose spatial constraints on the decision between mitosis and meiosis in the germline.

Alleles↗
PubMed1989

Genetics of intercellular signalling in C. elegans.

Cell-cell interactions play a significant role in controlling cell fate during development of the nematode Caenorhabditis elegans. It has been found that two genes, glp-1 and lin-12, are required for many of these decisions. glp-1 is required for induction of mitotic proliferation in the germline by the somatic distal tip cell and for induction of the anterior pharynx early in embryogenesis. lin-12 is required for the interactions between cells of equivalent developmental potential, which allow them to take on different fates. Comparison of these two genes on a molecular level indicates that they are similar in sequence and organization, suggesting that the mechanisms of these two different sets of cell-cell interactions are similar.

Animals↗
PubMed1988

Genetic control of sex determination in the germ line of Caenorhabditis elegans.

The nematode Caenorhabditis elegans normally exists as one of two sexes: self-fertilizing hermaphrodite or male. Development as hermaphrodite or male requires the differentiation of each tissue in a sex-specific way. In this review, I discuss the genetic control of sex determination in a single tissue of C. elegans: the germ line. Sex determination in the germ line depends on the action of two types of genes:--those that act globally in all tissues to direct male or female development and those that act only in the germ line to specify either spermatogenesis or oogenesis. First, I consider a tissue-specific sex-determining gene, fog-1, which promotes spermatogenesis in the germ line. Second, I consider the regulation of the hermaphrodite pattern of germ-line gametogenesis where first sperm and then oocytes are produced.

Animals↗