1
|
Roka Pun H, Karp X. An RNAi screen for conserved kinases that enhance microRNA activity after dauer in Caenorhabditis elegans. G3 (Bethesda) 2024; 14:jkae007. [PMID: 38226857 PMCID: PMC10917497 DOI: 10.1093/g3journal/jkae007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 10/17/2023] [Accepted: 01/05/2024] [Indexed: 01/17/2024]
Abstract
Gene regulation in changing environments is critical for maintaining homeostasis. Some animals undergo a stress-resistant diapause stage to withstand harsh environmental conditions encountered during development. MicroRNAs are one mechanism for regulating gene expression during and after diapause. MicroRNAs downregulate target genes posttranscriptionally through the activity of the microRNA-induced silencing complex. Argonaute is the core microRNA-induced silencing complex protein that binds to both the microRNA and to other microRNA-induced silencing complex proteins. The 2 major microRNA Argonautes in the Caenorhabditis elegans soma are ALG-1 and ALG-2, which function partially redundantly. Loss of alg-1 [alg-1(0)] causes penetrant developmental phenotypes including vulval defects and the reiteration of larval cell programs in hypodermal cells. However, these phenotypes are essentially absent if alg-1(0) animals undergo a diapause stage called dauer. Levels of the relevant microRNAs are not higher during or after dauer, suggesting that activity of the microRNA-induced silencing complex may be enhanced in this context. To identify genes that are required for alg-1(0) mutants to develop without vulval defects after dauer, we performed an RNAi screen of genes encoding conserved kinases. We focused on kinases because of their known role in modulating microRNA-induced silencing complex activity. We found RNAi knockdown of 4 kinase-encoding genes, air-2, bub-1, chk-1, and nekl-3, caused vulval defects and reiterative phenotypes in alg-1(0) mutants after dauer, and that these defects were more penetrant in an alg-1(0) background than in wild type. Our results implicate these kinases as potential regulators of microRNA-induced silencing complex activity during postdauer development in C. elegans.
Collapse
Affiliation(s)
- Himal Roka Pun
- Department of Biology, Central Michigan University, Mount Pleasant, MI 48859, USA
- Biochemistry, Cell and Molecular Biology Program, Central Michigan University, Mount Pleasant, MI 48859, USA
| | - Xantha Karp
- Department of Biology, Central Michigan University, Mount Pleasant, MI 48859, USA
- Biochemistry, Cell and Molecular Biology Program, Central Michigan University, Mount Pleasant, MI 48859, USA
| |
Collapse
|
2
|
Cuko L, Cale AR, Rambo L, Knoblock ML, Karp X. Distinct daf-16 isoforms regulate specification of vulval precursor cells in Caenorhabditis elegans. MicroPubl Biol 2022; 2022:10.17912/micropub.biology.000706. [PMID: 36575736 PMCID: PMC9790082 DOI: 10.17912/micropub.biology.000706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 12/05/2022] [Accepted: 12/07/2022] [Indexed: 12/29/2022]
Abstract
FOXO transcription factors regulate development, longevity, and stress-resistance across species. The C. elegans FOXO ortholog, daf-16, has three major isoforms with distinct promoters and N-termini. Different combinations of isoforms regulate different processes. Adverse environments can induce dauer diapause after the second larval molt. During dauer, daf-16 blocks specification of vulval precursor cells, including EGFR/Ras-mediated 1˚ fate specification and LIN-12/Notch-mediated 2˚ fate specification. Using isoform-specific mutants, we find that daf-16a and daf-16f are functionally redundant for the block to the expression of 1˚ fate markers. In contrast, all three isoforms contribute to blocking the expression of 2˚ fate markers.
Collapse
Affiliation(s)
| | - Allison R Cale
- Central Michigan University
,
Current address: University of Michigan, Ann Arbor
| | - Loni Rambo
- Central Michigan University
,
Current address: University of Michigan, Ann Arbor
| | | | - Xantha Karp
- Central Michigan University
,
Correspondence to: Xantha Karp (
)
| |
Collapse
|
3
|
Abstract
Diapause is a state of developmental arrest adopted in response to or in anticipation of environmental conditions that are unfavorable for growth. In many cases, diapause is facultative, such that animals may undergo either a diapause or a non-diapause developmental trajectory, depending on environmental cues. Diapause is characterized by enhanced stress resistance, reduced metabolism, and increased longevity. The ability to postpone reproduction until suitable conditions are found is important to the survival of many animals, and both vertebrate and invertebrate species can undergo diapause. The decision to enter diapause occurs at the level of the whole animal, and thus hormonal signaling pathways are common regulators of the diapause decision. Unlike other types of developmental arrest, diapause is programmed, such that the diapause developmental trajectory includes a pre-diapause preparatory phase, diapause itself, recovery from diapause, and post-diapause development. Therefore, developmental pathways are profoundly affected by diapause. Here, I review two conserved hormonal pathways, insulin/IGF signaling (IIS) and nuclear hormone receptor signaling (NHR), and their role in regulating diapause across three animal phyla. Specifically, the species reviewed are Austrofundulus limnaeus and Nothobranchius furzeri annual killifishes, Caenorhabditis elegans nematodes, and insect species including Drosophila melanogaster, Culex pipiens, and Bombyx mori. In addition, the developmental changes that occur as a result of diapause are discussed, with a focus on how IIS and NHR pathways interact with core developmental pathways in C. elegans larvae that undergo diapause.
Collapse
|
4
|
Affiliation(s)
- Allison R Cale
- Department of Chemistry and Biochemistry, Central Michigan University, Mount Pleasant, MI 48859.,Current address: Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109
| | - Xantha Karp
- Department of Biology, Central Michigan University, Mount Pleasant, MI 48859
| |
Collapse
|
5
|
Abstract
Dauer diapause is a stress-resistant, developmentally quiescent, and long-lived larval stage adopted by Caenorhabditis elegans when conditions are unfavorable for growth and reproduction. This chapter contains methods to induce dauer larva formation, to isolate dauer larvae, and to study pre- and post-dauer stages.
Collapse
Affiliation(s)
- Xantha Karp
- Department of Biology, Central Michigan University, Mount Pleasant, MI 48859 USA
| |
Collapse
|
6
|
Abstract
In C. elegans larvae, the execution of stage-specific developmental events is controlled by heterochronic genes, which include those encoding a set of transcription factors and the microRNAs that regulate the timing of their expression. Under adverse environmental conditions, developing larvae enter a stress-resistant, quiescent stage called 'dauer'. Dauer larvae are characterized by the arrest of all progenitor cell lineages at a stage equivalent to the end of the second larval stage (L2). If dauer larvae encounter conditions favorable for resumption of reproductive growth, they recover and complete development normally, indicating that post-dauer larvae possess mechanisms to accommodate an indefinite period of interrupted development. For cells to progress to L3 cell fate, the transcription factor Hunchback-like-1 (HBL-1) must be downregulated. Here, we describe a quiescence-induced shift in the repertoire of microRNAs that regulate HBL-1. During continuous development, HBL-1 downregulation (and consequent cell fate progression) relies chiefly on three let-7 family microRNAs, whereas after quiescence, HBL-1 is downregulated primarily by the lin-4 microRNA in combination with an altered set of let-7 family microRNAs. We propose that this shift in microRNA regulation of HBL-1 expression involves an enhancement of the activity of lin-4 and let-7 microRNAs by miRISC modulatory proteins, including NHL-2 and LIN-46. These results illustrate how the employment of alternative genetic regulatory pathways can provide for the robust progression of progenitor cell fates in the face of temporary developmental quiescence.
Collapse
Affiliation(s)
- Xantha Karp
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | | |
Collapse
|
7
|
Karp X, Hammell M, Ow MC, Ambros V. Effect of life history on microRNA expression during C. elegans development. RNA 2011; 17:639-651. [PMID: 21343388 PMCID: PMC3062175 DOI: 10.1261/rna.2310111] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Accepted: 01/11/2011] [Indexed: 05/30/2023]
Abstract
Animals have evolved mechanisms to ensure the robustness of developmental outcomes to changing environments. MicroRNA expression may contribute to developmental robustness because microRNAs are key post-transcriptional regulators of developmental gene expression and can affect the expression of multiple target genes. Caenorhabditis elegans provides an excellent model to study developmental responses to environmental conditions. In favorable environments, C. elegans larvae develop rapidly and continuously through four larval stages. In contrast, in unfavorable conditions, larval development may be interrupted at either of two diapause stages: The L1 diapause occurs when embryos hatch in the absence of food, and the dauer diapause occurs after the second larval stage in response to environmental stimuli encountered during the first two larval stages. Dauer larvae are stress resistant and long lived, permitting survival in harsh conditions. When environmental conditions improve, dauer larvae re-enter development, and progress through two post-dauer larval stages to adulthood. Strikingly, all of these life history options (whether continuous or interrupted) involve an identical pattern and sequence of cell division and cell fates. To identify microRNAs with potential functions in buffering development in the context of C. elegans life history options, we used multiplex real-time PCR to assess the expression of 107 microRNAs throughout development in both continuous and interrupted life histories. We identified 17 microRNAs whose developmental profile of expression is affected by dauer life history and/or L1 diapause, compared to continuous development. Hence these microRNAs could function to regulate gene expression programs appropriate for different life history options in the developing worm.
Collapse
Affiliation(s)
- Xantha Karp
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | | | | | | |
Collapse
|
8
|
Affiliation(s)
- Xantha Karp
- Department of Genetics, Dartmouth Medical School, Hanover, NH 03755, USA.
| | | |
Collapse
|
9
|
Karp X, Greenwald I. Multiple roles for the E/Daughterless ortholog HLH-2 during C. elegans gonadogenesis. Dev Biol 2004; 272:460-9. [PMID: 15282161 DOI: 10.1016/j.ydbio.2004.05.015] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2004] [Revised: 05/06/2004] [Accepted: 05/14/2004] [Indexed: 11/26/2022]
Abstract
HLH-2 is the Caenorhabditis elegans ortholog of the Drosophila Daughterless and mammalian E basic helix-loop-helix (bHLH) transcriptional activators that function during diverse events during animal development. HLH-2 has been implicated in cell fate specification in different neural lineages and in the LIN-12/Notch-mediated anchor cell (AC)/ventral uterine precursor cell (VU) decision in the somatic gonad. Here, we show that hlh-2 plays several distinct roles during somatic gonadogenesis. Our analysis suggests that hlh-2 is required to endow specific somatic gonadal cells with the competence to undergo the AC/VU decision, as well as functioning in the AC/VU decision per se; this novel "proAC" role appears to be analogous to the proneural role of Drosophila Daughterless. In addition to its two distinct roles in the specification of the AC, hlh-2 is also required for correct differentiation and function of the AC. hlh-2 also acts at an independent point in the gonadal lineage both to specify distal tip cells (DTCs) and in DTC differentiation and function.
Collapse
Affiliation(s)
- Xantha Karp
- Department of Genetics and Development, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA.
| | | |
Collapse
|
10
|
Karp X, Greenwald I. Post-transcriptional regulation of the E/Daughterless ortholog HLH-2, negative feedback, and birth order bias during the AC/VU decision in C. elegans. Genes Dev 2004; 17:3100-11. [PMID: 14701877 PMCID: PMC305261 DOI: 10.1101/gad.1160803] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The anchor cell/ventral uterine precursor cell (AC/VU) decision in Caenorhabditis elegans is a canonical example of lin-12/Notch-mediated lateral specification. Two initially equivalent cells interact via the receptor LIN-12 and its ligand LAG-2, so that one becomes the AC and the other a VU. During this interaction, feedback loops amplify a small difference in lin-12 activity, limiting lin-12 transcription to the presumptive VU and lag-2 transcription to the presumptive AC. Here, we find that hlh-2 appears to be required for the VU fate and directly activates lag-2 transcription in the presumptive AC. HLH-2 appears to accumulate selectively in the presumptive AC prior to differential transcription of lin-12 or lag-2, and is therefore the earliest detectable difference between the two cells undergoing the AC/VU decision. The restricted accumulation of HLH-2 to the presumptive AC reflects post-transcriptional down-regulation of HLH-2 in the presumptive VU. Our observations suggest that hlh-2 is regulated as part of the negative feedback that down-regulates lag-2 transcription in the presumptive VU. Finally, we show that the AC/VU decision in an individual hermaphrodite is biased by the relative birth order of the two cells, so that the first-born cell is more likely to become the VU. We propose models to suggest how birth order, HLH-2 accumulation, and transcription of lag-2 may be linked during the AC/VU decision.
Collapse
Affiliation(s)
- Xantha Karp
- Department of Genetics and Development, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA
| | | |
Collapse
|
11
|
Abstract
G2A is a heptahelical cell surface protein that has recently been described as a potential tumor suppressor, based on its ability to counteract transformation of pre-B cells and fibroblasts by Bcr-Abl, an oncogenic tyrosine kinase. We have isolated cDNAs encoding G2A in the course of screening libraries for clones that cause oncogenic transformation of NIH3T3 fibroblasts. When expressed at high levels in NIH3T3 cells by retroviral transduction, G2A induced a full range of phenotypes characteristic of oncogenic transformation, including loss of contact inhibition, anchorage-independent survival and proliferation, reduced dependence on serum, and tumorigenicity in mice. When expressed by transfection, G2A greatly enhanced the ability of a weakly oncogenic form of Raf-1 to transform NIH3T3 cells. These results demonstrate that G2A is potently oncogenic both on its own and in cooperation with another oncogene. Expression of G2A in fibroblasts and endothelial cells resulted in changes in cell morphology and cytoskeleton structure that were equivalent to those induced by the G protein subunit Galpha13. Transformation of NIH3T3 cells via G2A expression was completely suppressed by co-expression of LscRGS, a GTPase activating protein that suppresses signaling by Galpha12 and Galpha13. Hyperactivity of Galpha12 or Galpha13 has previously been shown to result in activation of Rho GTPases. G2A expression resulted in activation of Rho, and transformation via G2A was suppressed by a dominant negative form of RhoA. These results indicate that G2A may be directly coupled to Galpha13, and that it is the activation of this Rho-activating Galpha protein which is responsible for the ability of G2A to transform fibroblasts.
Collapse
MESH Headings
- 3T3 Cells/pathology
- Amino Acid Sequence
- Animals
- Cell Cycle Proteins/genetics
- Cell Cycle Proteins/metabolism
- Cell Transformation, Neoplastic
- Cytoskeleton/genetics
- Cytoskeleton/ultrastructure
- DNA, Complementary
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Endothelium, Vascular/pathology
- GTP-Binding Protein alpha Subunit, Gi2
- GTP-Binding Protein alpha Subunits, G12-G13
- GTP-Binding Protein alpha Subunits, Gi-Go
- GTP-Binding Protein alpha Subunits, Gq-G11
- GTP-Binding Proteins/genetics
- GTP-Binding Proteins/metabolism
- Genes, ras
- Hematopoietic Stem Cells/physiology
- Heterotrimeric GTP-Binding Proteins/metabolism
- Hybridomas
- Mice
- Molecular Sequence Data
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- Proto-Oncogene Proteins/metabolism
- Proto-Oncogene Proteins c-raf/genetics
- Proto-Oncogene Proteins c-raf/metabolism
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/metabolism
- Receptors, G-Protein-Coupled
- Serum Response Factor
- Signal Transduction
- Transcription, Genetic
- rac1 GTP-Binding Protein/genetics
- rac1 GTP-Binding Protein/metabolism
- rhoA GTP-Binding Protein/genetics
- rhoA GTP-Binding Protein/metabolism
Collapse
Affiliation(s)
- I E Zohn
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill 27599-7038, USA
| | | | | | | | | | | | | | | |
Collapse
|
12
|
Brown TJ, Shaw PA, Karp X, Huynh MH, Begley H, Ringuette MJ. Activation of SPARC expression in reactive stroma associated with human epithelial ovarian cancer. Gynecol Oncol 1999; 75:25-33. [PMID: 10502421 DOI: 10.1006/gyno.1999.5552] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVE SPARC (secreted protein, acidic, rich in cysteine) is a calcium-binding counteradhesive glycoprotein that has the potential to play an important role in promoting tumor progression and invasiveness. SPARC has been reported to be markedly down-regulated in ovarian carcinomas relative to the normal surface epithelium and has been suggested to act as a tumor suppressor in ovarian cancer. To more precisely define potential changes in SPARC expression associated with malignant transformation of the ovary, we compared the distribution of SPARC mRNA and protein expression in patient specimens of malignant and nonmalignant ovaries. METHOD SPARC mRNA and protein expression was examined in 24 human invasive ovarian cancers, 5 tumors of low malignant potential (LMP), and 8 nonmalignant ovaries by in situ hybridization and immunohistochemistry. RESULTS In nonmalignant ovaries, SPARC mRNA expression was restricted to thecal and granulosa cells of vessiculated follicles. Cytoplasmic SPARC immunoreactivity was observed in these compartments, whereas variable SPARC immunostaining was observed in normal surface epithelial cells. In contrast, high-level expression of SPARC mRNA and protein was detected in stroma of ovaries containing malignant tumor cells, particularly at the tumor-stromal interface of the invading tumors. Lower levels and a more diffuse pattern of SPARC mRNA expression were associated with LMP specimens. SPARC mRNA was not expressed by ovarian adenocarcinoma or by surface epithelial cells. Consistent with the in situ hybridization data, SPARC immunoreactivity was found throughout the reactive stroma of specimens containing ovarian carcinoma. However, despite the lack of detectable SPARC mRNA, SPARC immunoreactivity was consistently observed within the cytoplasm of cancer cells. CONCLUSION The pattern of SPARC expression shown in this study indicates that SPARC is up-regulated in reactive stroma associated with invasive ovarian cancer. Moreover, these results raise the possibility that SPARC secreted from the stroma is internalized by ovarian cancer cells and may exert important intracellular effects upon these cells.
Collapse
Affiliation(s)
- T J Brown
- Department of Obstetrics and Gynecology, University of Toronto, Ontario, Canada
| | | | | | | | | | | |
Collapse
|
13
|
Damjanovski S, Karp X, Funk S, Sage EH, Ringuette MJ. Ectopic expression of SPARC in Xenopus embryos interferes with tissue morphogenesis: identification of a bioactive sequence in the C-terminal EF hand. J Histochem Cytochem 1997; 45:643-55. [PMID: 9154151 DOI: 10.1177/002215549704500502] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
SPARC is a matricellular Ca(2+)-binding glycoprotein that exhibits both counteradhesive and antiproliferative effects on cultured cells. It is secreted by cells of various tissues as a consequence of morphogenesis, response to injury, and cyclic renewal and/or repair. In an earlier study with Xenopus embryos we had shown a highly specific and regulated pattern of SPARC expression. We now show that ectopic expression of SPARC before its normal embryonic activation produces severe anomalies, some of which are consistent with the functions of SPARC proposed from studies in vitro. Microinjection of SPARC RNA, protein, and peptides into Xenopus embryos before endogenous embryonic expression generated different but overlapping phenotypes. (a) Injection of SPARC RNA into one cell of a two-cell embryo resulted in a range of unilateral defects. (b) Precocious exposure of embryos to SPARC by microinjection of protein into the blastocoel cavity was associated with certain axial defects comparable to those obtained with SPARC RNA. (c) SPARC peptides containing follistatin-like and copper-binding sequences were without obvious effect, whereas SPARC peptide 4.2, corresponding to a disulfide-bonded, Ca(2+)-binding domain, was associated with a reduction in axial structures that led eventually to complete ventralization of the embryos. Histological analysis of ventralized embryos indicated that the morphogenetic events associated with gastrulation might have been inhibited. Microinjection of other Ca(2+)-binding glycoproteins, such as osteopontin and bone sialoprotein, resulted in phenotypes that were unique. We probed further the structural correlates of this region of SPARC in the context of tissue development. Co-injection of peptide 4.2 with Ca2+ or EGTA, and injection of peptide 4.2K (containing a mutated consensus Ca(2+)-binding sequence), demonstrated that the developmental defects associated with peptide 4.2 were independent of Ca2+. However, the disulfide bridge in this region of SPARC was found to be critical, as injection of peptide 4.2AA, a mutant lacking the cystine, generated no axial defects. We have therefore shown for the first time in vivo that the temporally inappropriate presence of SPARC is associated with perturbations in tissue morphogenesis. Moreover, we have identified at least one bioactive region of SPARC as the C-terminal disulfide-bonded, Ca(2+)-binding loop that was previously shown to be both counteradhesive and growth-inhibitory.
Collapse
Affiliation(s)
- S Damjanovski
- Department of Zoology, University of Toronto, Ontario, Canada
| | | | | | | | | |
Collapse
|