Biomedical subjects

S E Mango

Publications and source records attributed to S E Mango.

13 recordsLinked to original sources

PubMed2002

Regulation of organogenesis by the Caenorhabditis elegans FoxA protein PHA-4.

The pha-4 locus encodes a forkhead box A (FoxA/HNF3) transcription factor homolog that specifies organ identity for Caenorhabditis elegans pharyngeal cells. We used microarrays to identify pharyngeal genes and analyzed those genes to determine which were direct PHA-4 targets. Our data suggest that PHA-4 directly activates most or all pharyngeal genes. Furthermore, the relative affinity of PHA-4 for different TRTTKRY (R = A/G, K = T/G, Y = T/C) elements modulates the onset of gene expression, providing a mechanism to activate pharyngeal genes at different developmental stages. We suggest that direct transcriptional regulation of entire gene networks may be a common feature of organ identity genes.

Animals↗

PubMed2001

Early morphogenesis of the Caenorhabditis elegans pharynx.

We investigated the cellular behaviors that accompany the early stages of pharyngeal morphogenesis in Caenorhabditis elegans. The embryonic pharynx develops from a ball of cells into a linear tube connected anteriorly to the buccal cavity and posteriorly to the midgut. By using GFP reporters localized to discrete subcellular regions, we show that pharyngeal morphogenesis can be divided into three stages: (1) lengthening of the nascent pharyngeal lumen by reorientation of apicobasal polarity of anterior pharyngeal cells ("Reorientation"), (2) formation of an epithelium by the buccal cavity cells, which mechanically couples the buccal cavity to the pharynx and anterior epidermis ("Epithelialization"), and (3) a concomitant movement of the pharynx anteriorly and the epidermis of the mouth posteriorly to bring the pharynx, buccal cavity, and mouth into close apposition ("Contraction"). Several models can account for these cellular behaviors, and we distinguish between them by physically or genetically ablating cells within the digestive tract. These studies provide the first description of how the pharynx primordium develops into an epithelial tube, and reveal that pharyngeal morphogenesis resembles aspects of mammalian kidney tubulogenesis.

Animals↗

PubMed2001

Stop making nonSense: the C. elegans smg genes.

Cells monitor the quality of their mRNAs and degrade any transcripts that are poorly or incompletely translated. In the nematode Caenorhabditis elegans, degradation by the mRNA surveillance pathway depends on seven smg genes. Three of these genes also have a role in a second mRNA degradation pathway called RNA interference (RNAi), which is triggered by double-stranded RNA (dsRNA). Here I describe what is known about the smg genes and their potential functions in these two mRNA degradation pathways.

Animals↗

PubMed2000

A link between RNA interference and nonsense-mediated decay in Caenorhabditis elegans.

Double-stranded RNA (dsRNA) inhibits expression of homologous genes by a process involving messenger RNA degradation. To gain insight into the mechanism of degradation, we examined how RNA interference is affected by mutations in the smg genes, which are required for nonsense-mediated decay. For three of six smg genes tested, mutations resulted in animals that were initially silenced by dsRNA but then recovered; wild-type animals remained silenced. The levels of target messenger RNAs were restored during recovery, and RNA editing and degradation of the dsRNA were identical to those of the wild type. We suggest that persistence of RNA interference relies on a subset of smg genes.

Adenosine Deaminase↗

PubMed2000

The TBP-like factor CeTLF is required to activate RNA polymerase II transcription during C. elegans embryogenesis.

Metazoans possess two TATA-binding protein homologs, the general transcription factor TBP and a related factor called TLF. Four models have been proposed for the role of TLF in RNA polymerase II (Pol II) transcription: (1) TLF and TBP function redundantly, (2) TLF antagonizes TBP, (3) TLF is a tissue-specific TBP, or (4) TLF and TBP have distinct activities. Here we report that CeTLF is required to express a subset of Pol II genes and associates with at least one of these genes in vivo. CeTLF is also necessary to establish bulk transcription during early embryogenesis. Since CeTLF and CeTBP are expressed at comparable levels in the same cells, these findings suggest CeTLF performs a unique function in activating Pol II transcription distinct from that of CeTBP.

Amino Acid Sequence↗

PubMed1999

Patterning the C. elegans embryo: moving beyond the cell lineage.

The Caenorhabditis elegans embryo undergoes a series of stereotyped cell cleavages that generates the organs and tissues necessary for an animal to survive. Here we review two models of embryonic patterning, one that is lineage-based, and one that focuses on domains of organ and tissue precursors. Our evolving view of C. elegans embryogenesis suggests that this animal develops by mechanisms that are qualitatively similar to those used by other animals.

Animals↗

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↗

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↗

PubMed1994

Two maternal genes, apx-1 and pie-1, are required to distinguish the fates of equivalent blastomeres in the early Caenorhabditis elegans embryo.

In a 4-cell Caenorhabditis elegans embryo, two sister blastomeres called ABa and ABp are born with equivalent developmental potential, but eventually produce distinct patterns of cell fate. The different fates of ABa and ABp are specified at least in part by inductive interactions with neighboring blastomeres. Previous studies indicate that, at the 4-cell stage, a signal from the posterior-most blastomere, P2, is required for ABp to produce at least one of its unique cell types. This P2/ABp interaction depends on glp-1, a putative receptor for intercellular interactions. To investigate this early induction further, we isolated mutants in which ABp developed abnormally. We describe the effects of recessive mutations in apx-1, a maternal gene that appears to be required for P2 to signal ABp. In embryos from mothers homozygous for mutations in apx-1 (apx-1 embryos), ABp fails to produce its characteristic cell types. Instead, ABp from apx-1 embryos develops more like its sister ABa: it produces ABa-like pharyngeal cells and it recapitulates ABa-like cell lineages. Because mutations in apx-1 affect the development of only the ABp blastomere, we suggest that the wild-type gene encodes a component of the P2/ABp signalling pathway. To explain the observation that ABp in apx-1 embryos adopts an ABa-like fate, we propose a model in which the P2 signal is required to break the initial equivalence of ABa and ABp. We performed two independent tests of this model. First, we examined ABp development in pie-1 mutant embryos, in which P2 adopts the identity of another blastomere. We find that, in pie-1 embryos, APp fails to produce its characteristic cell types and instead adopts a fate similar to that of ABa. We conclude that the changed identity of P2 in pie-1 embryos prevents the P2/ABp interaction. As a second test, we examined ABp development in wild-type embryos after physically removing P2. These operated embryos produce extra pharyngeal cells, consistent with out proposal that a signal from P2 breaks the initially equivalent developmental state of ABa and ABp. We discuss the possibility that apx-1 acts as a ligand in this glp-1-dependent signalling pathway.

Animals↗

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↗

PubMed1990

cis-acting determinants of c-myc mRNA stability.

Rapid turnover of the c-myc message mediates both the low basal level of mRNA and the rapid response to changes in transcription. The primary RNA instability determinant (RID sequence) resides in the 3' untranslated region (UTR), within an 80 base region that is rich in A and U residues. In contrast to granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA in which the RID sequence has been mapped to a repeating AUUUA sequence, mutation of the only copy of this sequence in the c-myc 3' UTR has no effect on RNA turnover. Thus the c-myc RID sequence appears to be quite different from that of GM-CSF, which may account for the differential regulation of half-life exhibited by these mRNAs. c-myc mRNA turnover is also tightly coupled to translation since translational inhibitors stabilize this mRNA. Mutation of the initiating AUG to a termination codon stabilizes c-myc RNA, arguing that loading with polysomes (perhaps accompanied by localization on the cytoskeleton) is also required for proper message turnover.

Animals↗

PubMed1989

A nuclease-hypersensitive element of the human c-myc promoter interacts with a transcription initiation factor.

Transcription of the human c-myc oncogene is elaborately regulated, but the relevant molecular mechanisms are not yet understood. To begin to define elements and enzyme systems responsible for c-myc transcription in vitro, we partially purified a transcription factor essential for efficient and accurate in vitro initiation from the principal myc promoter, P2. DNA mobility shift assays located the factor binding domain at -142 to -115 with respect to the P1 promoter. This region contains pur/pyr sequences (predominantly purines in one strand), nuclease-hypersensitive sites (U. Siebenlist, L. Henninghausen, J. Battey, and P. Leder, Cell 37:381-391, 1984; C. Boles and M. Hogan, Biochemistry 26:367-376, 1987), and a triple-helix-forming element (M. Cooney, G. Czernuszewicz, E. Postel, S. Flint, and M. Hogan, Science 241:456-459, 1988). Methylation interference mapping established that the factor, termed PuF, directly contacts the repeated palindromic sequence GGGTGGG of the -142/-115 element. The interaction of PuF with this cis-acting element is necessary for P2 transcription in vitro, for (i) deletion of this 5' region from the myc promoter greatly reduced transcription efficiency and (ii) a synthetic duplex oligonucleotide corresponding to the -142/-115 sequence completely repressed c-myc transcription in the presence of the partially purified factor. These observations lend support to the hypothesis that pur/pyr sequences perform important biological roles in the regulation of c-myc gene expression, most likely by serving as transcription factor binding sites.

Base Composition↗

PubMed1989

Germ line c-myc is not down-regulated by loss or exclusion of activating factors in myc-induced macrophage tumors.

As in tumors with c-myc chromosomal translocations, c-myc retrovirus-induced monocyte tumors constitutively express an activated form of c-myc (the proviral gene), whereas the normal endogenous c-myc genes are transcriptionally silent. Treatment of these retrovirus-induced tumor cells with a number of bioactive chemicals and growth factors that are known to induce c-myc expression in cells of the monocyte lineage failed to induce the endogenous c-myc gene. In contrast, the same treatments induced the c-fos gene in both tumors and a control macrophage line. To investigate c-myc suppression further, a normal copy of the human c-myc gene was introduced into tumor and control cell lines by using a retrovirus with self-inactivating long terminal repeats. This transduced normal gene was expressed at equivalent levels in all cells, regardless of the state of endogenous c-myc gene expression, and was strongly induced by agents that induce the normal gene in the control cells. These results indicate that the signal transduction pathways that normally activate the c-myc gene are functional in myc-induced tumor cells and suggest that endogenous c-myc is actively suppressed. An examination of the c-myc locus itself showed that the lack of transcriptional activity correlated with the absence of several prominent DNase I-hypersensitive sites in the 5'-flanking region of the gene but without loss of general DNase sensitivity. Furthermore, analysis of 22 methylation-sensitive restriction enzyme sites in the 5'-flanking region, first exon, and first intron indicated that the silent c-myc genes remained in the same unmethylated state as did actively expressed genes. Thus, c-myc suppression does not appear to result from the most frequently described mechanisms of gene inactivation.

Animals↗