Chen, Chen-Shan et al. (2011) International Worm Meeting "The Checkpoint Protein PCH-2 Regulates Oocyte Quality in C. elegans ."

Ellis, Ronald, Chen, Chen-Shan

[International Worm Meeting, 2011]

As women age, they have a higher risk of producing a miscarriage or a child with birth defects. One contributing factor is that oocytes arrest development at the end of prophase of meiosis I and remain quiescent for many years, during which their quality declines. A major cause of this decline is the increasing fraction of oocytes with chromosomal abnormalities. To help minimize these failures, meiotic cells have checkpoint mechanisms that trigger cell cycle arrest in response to some chromosome problems, and cull faulty cells by initiating apoptosis. In C. elegans, the AAA ATPase PCH-2 monitors synapsis between homologous chromosomes, to ensure accurate meiotic segregation. If PCH-2 detects chromosomes that have not synapsed, it induces apoptosis. We are investigating whether the rate of asynapsis increases during aging, and if PCH-2 helps alleviate this increase. To see if the frequency of asynapsed chromosomes increases with age, we determined the fraction of XO male progeny produced by aging hermaphrodites, since problems with chromosome segregation should lead to a higher fraction of males. We observed a 10-fold increase in the fraction of males produced by older hermaphrodites, as well as an increase in the fraction of defective embryos. Furthermore, both effects were aggravated by a mutation in pch-2. Although PCH-2 helped maintain oocyte quality at all ages, its relative importance was greatest in young animals, which raises the possibility that PCH-2 activity does not increase enough with age to cope with mounting problems in chromosome segregation.

Chao-Kung Chen et al. (2003) International Worm Meeting "CGC and WormBase"

Keith Bradnam, Theresa Stiernagle, Richard Durbin, Jonathan Hodgkin, Chao-Kung Chen

[International Worm Meeting, 2003]

Nansheng Chen et al. (2003) International Worm Meeting "Wormbase as a Data Mining Resource"

Lincoln D Stein, Nansheng Chen

[International Worm Meeting, 2003]

Chen, Xiaoyin et al. (2013) International Worm Meeting "Neuromodulation of C. elegans mechanosensation."

Chen, Xiaoyin, Chalfie, Martin

[International Worm Meeting, 2013]

Sensory perception is modified by cues detected by the sensory cells themselves and from signals initiated by other sensory cells. We show that mechanosensation in the touch receptor neurons (TRNs), which receive no synaptic input, is modulated by both mechanical and non-mechanical cues. These signals alter touch sensitivity through two signaling pathways that modulate touch sensitivity by converging on a common mechanism. Sustained mechanical signals, such as continuous vibration, increase TRN sensitivity to force. This long-term sensitization requires the activation of a secondary mechanosensory system involving the integrins and is independent of the MEC-4 mechanotransduction channels. Non-mechanical stress cues, such as dauer formation, hypoxia, and high salt, reduce touch sensitivity by reducing the expression of two insulin-like peptides, INS-10 and INS-22, which act as long-range neuromodulators to activate insulin signaling in the TRNs. Both insulin and integrin signaling compensate for each other and converge by using AKT-1 and DAF-16. Loss of AKT-1 activity increases the transcription of mfb-1, which reduces the amount of MEC-4 mechanotransduction channel available on the plasma membrane, thus changing the TRN sensitivity to force. These alterations in TRN sensitivity adjust the acuity and priority of the touch response to benefit the animal under diverse conditions. During sustained background stimulation, habituation reduces the response to background stimuli, but long-term sensitization counters habituation to maintain TRN response to strong stimuli, thus distinguishing background stimulation from stronger signals. The reduction of touch sensitivity under non-mechanical stress conditions increases the efficiency of the animal's ability to do non-mechanosensory tasks. For example chemotaxis is more efficient in the presence of mechanical distractions. Thus, modulation of touch can alter the balance between senses to prioritize sensory responses that can facilitate an escape from the stress conditions. Our findings demonstrate a non-synaptic neuromodulatory network that integrates multi-modal signals and alters behavior to optimize the animal's response to multiple conditions.

Chen WJ et al. (1997) International C. elegans Meeting "SUPPRESSORS OF ACTIVATED C.ELEGANS GOA"

Hajdu-Cronin YM, Sternberg PW, Chen WJ

[International C. elegans Meeting, 1997]

Goa is involved in several C. elegans behaviors such as egglaying, movement and feeding. 21 independent suppressors of a Goa gain-of-function mutant under the control of a heat shock promoter (syIs17) were isolated from 21,000 EMS-mutagenized gametes. These define 7 complementation groups and can be divided into 3 classes according to the behavior. Class 1 includes sag-1 X and sag-2 I. They are hyperactive, egg-laying constitutive and have empty uteri; as are Goa(lf) mutants. Class 2 includes sag-3 I, sag-5 III and sag-7 X, mimics the phenotype of Goa(gf) in the egglaying deficiency and drug resistance. Class 3 includes sag-4,V and sag-6. They are nearly wild type in appearance and behavior. Double mutants between different classes suppress syIs17 better than when they are alone, indicating that the three classes of genes act in different aspects of Goa regulation. Class 1 may encode components of Goa pathway in the tissues where Goa is usually expressed since they suppress syIs9, a Goa(gf) mutant under its own promoter. Class 2 and 3 may function in other tissues which, when Goa is misexpressed, causes lethality and more severe defect in movement and feeding than syIs9. We are mapping these genes further.

Chen LS et al. (1991) International C. elegans Meeting "TOWARDS A MUTANT IN THE CeMyoD GENE."

Fire A, Krause MW, Weintraub H, Chen LS

[International C. elegans Meeting, 1991]

C. elegans MyoD is a nuclear protein expressed in body wall muscle precursors during early embryogenesis; it does not appear to be expressed in either pharyngeal muscle cells or nonmuscle lineages (1). We are attempting to create mutations in the gene (hlh-1) encoding CeMyoD to determine its role in defining body wall muscle cell fates. It is assumed that mutations affecting hlh-l will interfere in the development of body wall muscle cells, which may cause embryonic lethality. Presently, there are no known MyoD mutations for any organism. hlh-l is located on the left arm of chromosome 11, and is closely linked to dpy-25 (dpy-25 is defined by the dominant allele e817). We have obtained fourteen apparent deficiencies in the region ( by reverting dpy-25) and are mapping these to determine which of them delete hlh-l. In addition, we are beginning a general screen for lethal mutants in this region of chromosome 11. Candidates will be tested by genetic and molecular criteria (eg. map position and transformation rescue) to identify hlh-l alleles.

Chen W et al. (1998) West Coast Worm Meeting "Goa SIGNALING IN C. ELEGANS"

Sternberg PW, Hajdu-Cronin YM, Chen W

[West Coast Worm Meeting, 1998]

Goa is involved in several C. elegans behaviors such as egg-laying, movement and feeding (Mendel et al., 1995 and Ségalat et al., 1995). We isolated 24 independent mutations that revert the phenotype of syIs17 ( a Goa gain-of-function transgenic integrant under the control of a heat shock promoter). These define 8 complementation groups named sags (Suppressors of Activated Goa). Two of the complemetation groups, sag-1 and sag-2, appear to act in Goa signaling based on several experiments. Animals deficient in either gene are hyperactive, egg-laying constitutive and have empty uteri; as do goa-1 loss-of-function mutants. Western blot analysis indicates that heat-shock induced GOA-1 is not affected in sag-1 and sag-2 strains and thus these mutations likely affect Goa signaling rather than its synthesis. sag-1 and sag-2 also suppress syIs9, an integrated strain with activated Goa under its own promoter, indicating that they act in cells that normally express GOA-1. sag-1 is allelic to dgk-1 which encodes a Diacylglycerol Kinase (Nurrish et al., page 44, 1997 international C. elegans meeting). We have positionally cloned sag-2 and find that it encodes a RGS protein (Regulators of G protein Signaling), raising the possibility that RGS proteins act as effectors as well as regulators of G proteins. SAG-2 might also act as an effector of GOA-1 that inhibits signaling by another Ga subunit.

Chen, Ling et al. (2009) International Worm Meeting "Analysis of CED-4-dependent cell size control."

Rothman, Joel H., Chen, Ling

[International Worm Meeting, 2009]

Cells, organs, and organisms reach a reproducible size appropriate for their functions through the interconnected and complementary action of cell size regulation, cell proliferation, and apoptosis. Coordination of these processes is critical for normal development and their dysregulation can lead to pathologies such as tumor formation. Though apoptosis and cell size regulation are controlled by largely distinct molecular regulatory events, we found that these two critical processes are linked by the action of several factors, including TFG-1, the homologue of the human proto-oncogene TFG (TRK-fused gene), and the pro-apoptotic regulator CED-4. We found that while TFG-1 is a suppressor of apoptosis, its removal leads to decreased cell and nuclear volume, resulting in small adults (Sma phenotype). Mutations in ced-4 suppress this defect in cell and nuclear size. However, simultaneous inactivation of the CED-3 and CSP-1 caspases does not suppress the diminutive cell size of adult tfg-1(RNAi) worms, suggesting that CED-4 acts through a caspase-independent mechanism to suppress cell growth. We found that CED-4 acts broadly to antagonize the action of a number of cell size-regulating proteins, including cAMP response element-binding (CREB) protein, translation initiation factor eIF2B, and the nucleolar p53-interacting protein nucleostemin, but not those functioning in the TGF-beta signaling pathway. CED-4-regulated body and cell size control is highly correlated with total protein level, suggesting that CED-4 might regulate cell size through modulation of protein production and accumulation. To better understand the role of CED-4 in cell size regulation, we conducted functional genomics screens for genes required for CED-4-dependent body and cell size regulation. Consistent with our observed correlation between CED-4-dependent cell size and protein content, genes involved in protein synthesis, including ribosomal structure proteins, aminoacyl-tRNA synthetases, and translation initiation factors, are enriched in the screen. Moreover, genes functioning in metabolic processes, including lipid metabolism and glycolysis, also affect body size in a CED-4-dependent manner, suggesting that metabolic changes might also contribute to CED-4-dependent cell size regulation. Thus, in addition to its central role in apoptosis, CED-4 performs a critical role in limiting cellular growth.

Pin-An Chen et al. (2007) International Worm Meeting "Identifying suppressors of an activated Go mutant."

Pin-An Chen, Erik Jorgensen

[International Worm Meeting, 2007]

Neurotransmission is modulated by G protein pathways. In C. elegans, Gq signaling is the major stimulatory pathway regulating neurotransmitter release. Conversely, Go plays an inhibitory role in neurotransmission, possibly by negatively regulating the Gq signaling. However, the downstream effectors of Go<font face=symbol>a</font> remain unclear. To characterize the Go pathway, we screened for suppressors of the activated Go<font face=symbol>a</font> mutant unc-109(n499ox304). unc-109(n499ox304) mutant worms are paralyzed and have a straight body posture. We screened approximately 24,000 haploid genomes for mutants that suppress the paralyzed movement or the straight body posture phenotype of unc-109(n499ox304). 17 candidate mutants were identified including two eat-16 mutants. EAT-16 is the RGS protein specific for Gq<font face=symbol>a</font>, and mutations in eat-16 were previously shown to suppress the paralyzed phenotype of animals overexpressing goa-1 (Hajdu-Cronin et al., 1999). In addition to eat-16, we also identified a dominant suppressor which is a gain-of-function allele of nca-1. nca-1 encodes a novel conserved channel, which we believe may be a target of G protein signaling. I am now in the process of mapping and characterizing the other candidate suppressors.

Chen WI et al. (1997) International C. elegans Meeting "REGULATION OF ceh-22 GENE EXPRESSION"

Okkema PG, Chen WI

[International C. elegans Meeting, 1997]

The NK-2 class homeobox gene ceh-22 is a key component of a cell type-specific pathway activating pharyngeal muscle gene expression. ceh-22 is specifically expressed early in the development of most pharyngeal muscles, shortly after these cells are born, and it is the earliest known marker of pharyngeal muscle differentiation. Previous work has shown that ceh-22 is regulated at the level of transcription and that a lacZ reporter gene containing 4.5kb of ceh-22 5!-flanking DNA is expressed identically to the endogenous gene. To identify upstream mechanisms controlling pharyngeal muscle gene expression, we have begun to characterize the ceh-22 promoter by transformation assay in C. elegans. A series of 5! deletions of the ceh-22::lacZ reporter indicate that 1.4kb of upstream sequences is sufficient for ceh-22 expression; further deletions result in reduced expression. Within the ceh-22 promoter region, we have identified two distinct transcriptional enhancers, referred to as the distal enhancer and the proximal enhancer. The distal enhancer is a more general regulatory element required for high level expression of ceh-22::lacZ. The proximal enhancer is more specific and it is primarily active in the pharyngeal muscles where ceh-22 is expressed. We are currently examining the temporal and spatial patterns of proximal and distal enhancer activities, and identifying the minimal fragment containing the proximal enhancer.