While gustatory sensing of the five primary flavors (sweet, salty, sour, bitter, and savory) has been extensively studied, pathways that detect non-canonical taste stimuli remain relatively ...unexplored. In particular, while reactive oxygen species cause generalized damage to biological systems, no gustatory mechanism to prevent ingestion of such material has been identified in any organism. We observed that light inhibits C. elegans feeding and used light as a tool to uncover molecular and neural mechanisms for gustation. Light can generate hydrogen peroxide, and we discovered that hydrogen peroxide similarly inhibits feeding. The gustatory receptor family members LITE-1 and GUR-3 are required for the inhibition of feeding by light and hydrogen peroxide. The I2 pharyngeal neurons increase calcium in response to light and hydrogen peroxide, and these responses require GUR-3 and a conserved antioxidant enzyme peroxiredoxin PRDX-2. Our results demonstrate a gustatory mechanism that mediates the detection and blocks ingestion of a non-canonical taste stimulus, hydrogen peroxide.
•Light and hydrogen peroxide (H2O2) cause C. elegans to inhibit feeding and escape•Light and H2O2 are sensed via the gustatory receptor orthologs GUR-3 and LITE-1•The I2 pharyngeal neurons detect light and H2O2 via GUR-3 and peroxiredoxin PRDX-2•C. elegans light sensing likely occurs via generation of reactive oxygen species
Is there more to taste than the five primary flavors? Bhatla et al. describe how C. elegans tastes and behaviorally responds to hydrogen peroxide. This sensing mechanism is also used to detect light, suggesting that light sensing in the worm relies on the tasting of reactive oxygen species.
The life span of Caenorhabditis elegans is controlled by signaling between the germline and the soma. Germ cell removal extends life span by triggering the activation of the DAF-16/FOXO transcription ...factor in the intestine. Here we analyze microRNA function in C. elegans aging and show that the microRNA mir-71 functions to mediate the effects of germ cell loss on life span. mir-71 is required for the life span extension caused by germline removal, and overexpression of mir-71 further extends the life span of animals lacking germ cells. mir-71 functions in the nervous system to facilitate the localization and transcriptional activity of DAF-16 in the intestine. Our findings reveal a microRNA-dependent mechanism of life span regulation by the germline and indicate that signaling among the gonad, the nervous system, and the intestine coordinates the life span of the entire organism.
► C. elegans life span extension caused by germ cell loss depends on the microRNA mir-71 ► mir-71 functions in neurons to promote germline-mediated longevity ► mir-71-mediated life span extension depends on intestinal daf-16 function ► mir-71 facilitates the localization and activity of DAF-16 in the intestine
A non-coding hexanucleotide repeat expansion in the C9ORF72 gene is the most common mutation associated with familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). To ...investigate the pathological role of C9ORF72 in these diseases, we generated a line of mice carrying a bacterial artificial chromosome containing exons 1 to 6 of the human C9ORF72 gene with approximately 500 repeats of the GGGGCC motif. The mice showed no overt behavioral phenotype but recapitulated distinctive histopathological features of C9ORF72 ALS/FTD, including sense and antisense intranuclear RNA foci and poly(glycine-proline) dipeptide repeat proteins. Finally, using an artificial microRNA that targets human C9ORF72 in cultures of primary cortical neurons from the C9BAC mice, we have attenuated expression of the C9BAC transgene and the poly(GP) dipeptides. The C9ORF72 BAC transgenic mice will be a valuable tool in the study of ALS/FTD pathobiology and therapy.
•Mouse model expressing ALS/FTD associated C9ORF72 hexanucleotide repeat expansion•Formation of sense and antisense C9ORF72 RNA transcript foci•Dipeptide repeat proteins produced by repeat-associated non-ATG translation•Formation of cytoplasmic inclusions containing dipeptide repeat proteins
Peters et al. report that transgenic mice expressing ALS/FTD-associated C9ORF72 hexanucleotide expansions develop histopathological features of c9ALS/FTD (RNA foci and aggregates of non-ATG translated dipeptides) but not motor neuron disease. These features are attenuated in vitro by anti-C9ORF72 microRNA.
The most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is the expansion of a hexanucleotide repeat in a non-coding region of the gene C9orf72. We ...report that loss-of-function mutations in alfa-1, the Caenorhabditis elegans ortholog of C9orf72, cause a novel phenotypic defect: endocytosed yolk is abnormally released into the extra-embryonic space, resulting in refractile “blobs.” The alfa-1 blob phenotype is partially rescued by the expression of the human C9orf72 protein, demonstrating that C9orf72 and alfa-1 function similarly. We show that alfa-1 and R144.5, which we identified from a genetic screen for mutants with the blob phenotype and renamed smcr-8, act in the degradation of endolysosomal content and subsequent lysosome reformation. The alfa-1 abnormality in lysosomal reformation results in a general dysregulation in lysosomal homeostasis, leading to defective degradation of phagosomal and autophagosomal contents. We suggest that, like alfa-1, C9orf72 functions in the degradation of endocytosed material and in the maintenance of lysosomal homeostasis. This previously undescribed function of C9orf72 explains a variety of disparate observations concerning the effects of mutations in C9orf72 and its homologs, including the abnormal accumulation of lysosomes and defective fusion of lysosomes to phagosomes. We suggest that aspects of the pathogenic and clinical features of ALS/FTD caused by C9orf72 mutations, such as altered immune responses, aggregation of autophagy targets, and excessive neuronal excitation, result from a reduction in C9orf72 gene function and consequent abnormalities in lysosomal degradation.
•C. elegans alfa-1 mutations cause yolk release into the extra-embryonic space•alfa-1 functions in the degradation of endocytosed material•Lysosomal reformation and lysosomal homeostasis are altered in alfa-1 mutants•alfa-1 and the human ALS gene C9orf72 act in similar molecular genetic pathways
Corrionero and Horvitz show that the C. elegans gene alfa-1 functions in the degradation of endocytosed material and hence has effects on subsequent lysosomal reformation and lysosomal homeostasis maintenance. Human C9orf72 functions similarly. Aspects of ALS/FTD might result from decreased C9orf72 function and defective lysosomal degradation.
A classic feature of apoptotic cells is the cell-surface exposure of phosphatidylserine (PtdSer) as an "eat me" signal for engulfment. We show that the Xk-family protein Xkr8 mediates PtdSer exposure ...in response to apoptotic stimuli. Mouse Xkr8 -/- cells or human cancer cells in which Xkr8 expression was repressed by hypermethylation failed to expose PtdSer during apoptosis and were inefficiently engulfed by phagocytes. Xkr8 was activated directly by caspases and required a caspase-3 cleavage site for its function. CED-8, the only Caenorhabditis elegans Xk-family homolog, also promoted apoptotic PtdSer exposure and cell-corpse engulfment. Thus, Xk-family proteins have evolutionarily conserved roles in promoting the phagocytosis of dying cells by altering the phospholipid distribution in the plasma membrane.
Although replication-coupled chromatin assembly is known to be important for the maintenance of patterns of gene expression through sequential cell divisions, the role of replication-coupled ...chromatin assembly in controlling cell differentiation during animal development remains largely unexplored. Here we report that the CAF-1 protein complex, an evolutionarily conserved histone chaperone that deposits histone H3-H4 proteins onto replicating DNA, is required to generate a bilateral asymmetry in the
C. elegans nervous system. A mutation in 1 of 24
C. elegans histone H3 genes specifically eliminates this aspect of neuronal asymmetry by causing a defect in the formation of a histone H3-H4 tetramer and the consequent inhibition of CAF-1-mediated nucleosome formation. Our results reveal that replication-coupled nucleosome assembly is necessary to generate a bilateral asymmetry in
C. elegans neuroanatomy and suggest that left-right asymmetric epigenetic regulation can establish bilateral asymmetry in the nervous system.
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► CAF-1 is required for a neuronal bilateral asymmetry in
C. elegans ► A mutation in 1 of 24 histone H3 genes specifically eliminates this asymmetry ► Mutant histone H3 proteins inhibit CAF-1-mediated nucleosome formation ► A defect in the formation of H3-H4 tetramers causes loss of bilateral asymmetry
Mutation of a histone H3 gene in
C. elegans disrupts the left-right asymmetry of a pair of neurons, revealing a role for asymmetric nucleosome assembly in development.
MicroRNAs (miRNAs) are approximately 23 nt regulatory RNAs that posttranscriptionally inhibit the functions of protein-coding mRNAs. We previously found that most C. elegans miRNAs are individually ...not essential for development or viability and proposed that paralogous miRNAs might often function redundantly 1. To test this hypothesis, we generated mutant C. elegans strains that each lack multiple or all members of one of 15 miRNA families. Mutants for 12 of these families did not display strong synthetic abnormalities, suggesting that these miRNA families have subtle roles during development. By contrast, mutants deleted for all members of the mir-35 or mir-51 families died as embryos or early larvae, and mutants deleted for four members of the mir-58 family showed defects in locomotion, body size, and egg laying and an inability to form dauer larvae. Our findings indicate that the regulatory functions of most individual miRNAs and most individual families of miRNAs related in sequence are not critical for development or viability. Conversely, because in some cases miRNA family members act redundantly, our findings emphasize the importance of determining miRNA function in the absence of miRNAs related in sequence.
► Many miRNA families are not critical for C. elegans development or viability ► The mir-35 and mir-51 families are required for normal embryonic development ► The mir-58 family is required for normal development and behavior
MicroRNA Expression in Zebrafish Embryonic Development Wienholds, Erno; Kloosterman, Wigard P; Miska, Eric ...
Science (American Association for the Advancement of Science),
07/2005, Volume:
309, Issue:
5732
Journal Article
Peer reviewed
MicroRNAs (miRNAs) are small noncoding RNAs, about 21 nucleotides in length, that can regulate gene expression by base-pairing to partially complementary mRNAs. Regulation by miRNAs can play ...essential roles in embryonic development. We determined the temporal and spatial expression patterns of 115 conserved vertebrate miRNAs in zebrafish embryos by microarrays and by in situ hybridizations, using locked-nucleic acid-modified oligonucleotide probes. Most miRNAs were expressed in a highly tissue-specific manner during segmentation and later stages, but not early in development, which suggests that their role is not in tissue fate establishment but in differentiation or maintenance of tissue identity.
The proper regulation of apoptosis requires precise spatial and temporal control of gene expression. While the transcriptional and translational activation of pro-apoptotic genes is known to be ...crucial to triggering apoptosis, how different mechanisms cooperate to drive apoptosis is largely unexplored. Here we report that pro-apoptotic transcriptional and translational regulators act in distinct pathways to promote programmed cell death. We show that the evolutionarily conserved C. elegans translational regulators GCN-1 and ABCF-3 contribute to promoting the deaths of most somatic cells during development. GCN-1 and ABCF-3 are not obviously involved in the physiological germ-cell deaths that occur during oocyte maturation. By striking contrast, these proteins play an essential role in the deaths of germ cells in response to ionizing irradiation. GCN-1 and ABCF-3 are similarly co-expressed in many somatic and germ cells and physically interact in vivo, suggesting that GCN-1 and ABCF-3 function as members of a protein complex. GCN-1 and ABCF-3 are required for the basal level of phosphorylation of eukaryotic initiation factor 2α (eIF2α), an evolutionarily conserved regulator of mRNA translation. The S. cerevisiae homologs of GCN-1 and ABCF-3, which are known to control eIF2α phosphorylation, can substitute for the worm proteins in promoting somatic cell deaths in C. elegans. We conclude that GCN-1 and ABCF-3 likely control translational initiation in C. elegans. GCN-1 and ABCF-3 act independently of the anti-apoptotic BCL-2 homolog CED-9 and of transcriptional regulators that upregulate the pro-apoptotic BH3-only gene egl-1. Our results suggest that GCN-1 and ABCF-3 function in a pathway distinct from the canonical CED-9-regulated cell-death execution pathway. We propose that the translational regulators GCN-1 and ABCF-3 maternally contribute to general apoptosis in C. elegans via a novel pathway and that the function of GCN-1 and ABCF-3 in apoptosis might be evolutionarily conserved.
The elimination of unnecessary or defective cells from metazoans occurs during normal development and tissue homeostasis, as well as in response to infection or cellular damage. Although many cells ...are removed through caspase-mediated apoptosis followed by phagocytosis by engulfing cells, other mechanisms of cell elimination occur, including the extrusion of cells from epithelia through a poorly understood, possibly caspase-independent, process. Here we identify a mechanism of cell extrusion that is caspase independent and that can eliminate a subset of the Caenorhabditis elegans cells programmed to die during embryonic development. In wild-type animals, these cells die soon after their generation through caspase-mediated apoptosis. However, in mutants lacking all four C. elegans caspase genes, these cells are eliminated by being extruded from the developing embryo into the extra-embryonic space of the egg. The shed cells show apoptosis-like cytological and morphological characteristics, indicating that apoptosis can occur in the absence of caspases in C. elegans. We describe a kinase pathway required for cell extrusion involving PAR-4, STRD-1 and MOP-25.1/-25.2, the C. elegans homologues of the mammalian tumour-suppressor kinase LKB1 and its binding partners STRADα and MO25α. The AMPK-related kinase PIG-1, a possible target of the PAR-4–STRD-1–MOP-25 kinase complex, is also required for cell shedding. PIG-1 promotes shed-cell detachment by preventing the cell-surface expression of cell-adhesion molecules. Our findings reveal a mechanism for apoptotic cell elimination that is fundamentally distinct from that of canonical programmed cell death.
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