The Caenorhabditis elegans defecation motor program (DMP) is a highly coordinated rhythmic behavior that requires two GABAergic neurons that synapse onto the enteric muscles. One class of DMP mutants, called anterior body wall muscle contraction and expulsion defective (aex) mutants, exhibits similar defects to those caused by the loss of these two neurons. Here, we demonstrate that aex-2 encodes a G-protein-coupled receptor (GPCR) and aex-4 encodes an exocytic SNAP25 homologue. We found that aex-2 functions in the nervous system and activates a Gs␣ signaling pathway to regulate defecation. aex-4, on the other hand, functions in the intestinal epithelial cells. Furthermore, we show that aex-5, which encodes a pro-protein convertase, functions in the intestine to regulate the DMP and that its secretion from the intestine is impaired in aex-4 mutants. Activation of the Gs␣ GPCR pathway in GABAergic neurons can suppress the defecation defect of the intestinal mutants aex-4 and aex-5. Lastly, we demonstrate that activation of GABAergic neurons using the light-gated cation channel channelrhodopsin-2 is sufficient to suppress the behavioral defects of aex-2, aex-4, and aex-5. These results genetically place intestinal genes aex-4 and aex-5 upstream of GABAergic GPCR signaling. We propose a model whereby the intestinal genes aex-4 and aex-5 control the DMP by regulating the secretion of a signal, which activates the neuronal receptor aex-2. T he Caenorhabditis elegans defecation motor program (DMP)is a highly coordinated series of three muscle contractions that are executed every 45 sec [ Fig. 1A and supporting information (SI) Movie S1]. The cycle is initiated by a posterior body wall muscle contraction (pBoc), followed 2-3 sec later by an anterior body wall muscle contraction (aBoc). About 1 sec after the aBoc, enteric muscles contract, thus causing the expulsion (Exp) of intestinal contents. The process repeats itself Ϸ45 sec later with little variability in the timing of contractions (1). A genetic screen for mutants that displayed defects in the DMP isolated mutants defective in each of the three muscle contractions, known as pbo, abo, and exp (1). The screen also recovered mutants defective in the last two muscle contractions (aBoc and Exp [aex]) and mutants defective in the cycle periodicity (i.e., longer or shorter than normal DMP cycling times) (1). Molecular studies of these mutants have suggested that the behavior is orchestrated through the communication between the intestine, GABAergic neurons, and muscle.The periodicity of the DMP is regulated by the C. elegans intestine, a single-cell layer tube of polarized epithelial cells joined by gap junctions (2, 3). Intestinal Ca 2ϩ oscillations with Ϸ45-sec periodicity appear to play a central role in this timing. They consist of a posterior-to-anterior Ca 2ϩ wave whose levels peak in the posterior and anterior intestinal cells just before the pBoc and aBoc contractions, respectively (3-5). Mutations in genes involved in the maintenance of Ca 2ϩ oscillations or i...

The genetic positions of the five Arabidopsis thaliana centromere regions have been identified by mapping size polymorphisms in the centromeric 180-bp repeat arrays. Structural and genetic analysis indicates that 180-bp repeat arrays of up to 1000 kb are found in the centromere region of each chromosome. The genetic behavior of the centromeric arrays suggests that recombination within the arrays is suppressed. These results indicate that the centromere regions of A. thaliana resemble human centromeres in size and genomic organization.Genetic mapping of centromeres is essential for the integration of cytological and genetic maps, and marks an important step toward the molecular characterization of centromeric DNA. Although the centromere is one of the most conspicuous markers on the cytological map, determination of the location of centromeres on genetic maps is frequently difficult to achieve. This is especially true in higher animals and plants where the genetic tools for centromere mapping are limited.We have been pursuing the characterization of centromere regions of the model angiosperm Arabidopsis thaliana. This plant's small genome (∼100 Mb/haploid) (Meyerowitz 1994) and relatively low abundance of repetitive DNA [∼10% of total (Leutwiler et al. 1984)] make it well suited for molecular chromosome studies. Aiding in this analysis is the availability of dense genetic maps that exist for each of A. thaliana's five chromosomes (e.g., Hauge et al. 1993;Lister and Dean 1993). In addition, physical maps are being developed for all A. thaliana chromosomes in the form of overlapping cloned genomic fragments (Schmidt et al. 1995;Zachgo et al. 1996).Considering the generally advanced molecular characterization of the A. thaliana genome, the genomic organization and genetic location of centromeres in this species remain poorly characterized. The A. thaliana centromere regions are heterochromatic (Schweizer et al. 1987) and contain tandem arrays of related repeats (exhibiting ജ80% similarity) that are ∼180 bp in length (Martinez-Zapater et al. 1986;Simoens et al. 1988;Maluszynska and Heslop-Harrison 1991), a genomic organization that resembles the ∼170-bp alphoid repeat arrays at primate centromeres (Willard 1990;Pluta et al. 1995). It is not clear whether the 180-bp repeat arrays flank or span A. thaliana centromeres, but data from mammalian systems suggest that the alphoid repeats are intimately associated with the centromere and are likely to play a role in centromere function (Heartlein et al. 1988;Haaf et al. 1992;Tyler-Smith et al. 1993;Brown et al. 1994;Larin et al. 1994;Harrington et al. 1997). A number of other middlerepetitive sequence elements have been found to be associated with the 180-bp repeats in genomic clones (Richards et al. 1991;Schmidt et al. 1995;Pelissier et al. 1996; Thompson et al. 1996a,b), suggesting that islands of more complex sequence arrangement are located in the A. thaliana centromeric regions.An approximate genetic location of three of the five A. thaliana centromeres (on chromosomes ...

This is the first study to report changes in nicotine delivery and biomarkers of tobacco exposure following a short-term product switch from CCs to either an EC or NG in a controlled environment. The study shows that nicotine exposure decreased in both groups but was maintained closer to CC smoking with the EC groups. Biomarkers of tobacco combustion decreased to similar levels in both EC and gum groups.

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Biomarkers of exposure (BoE) can help evaluate exposure to combustion-related, tobacco-specific toxicants after smokers switch from cigarettes to potentially less-harmful products like electronic nicotine delivery systems (ENDS). This paper reports data for one (Vuse Solo Original) of three products evaluated in a randomized, controlled, confinement study of BoE in smokers switched to ENDS. Subjects smoked their usual brand cigarette ad libitum for two days, then were randomized to one of three ENDS for a 7-day ad libitum use period, or to smoking abstinence. Thirteen BoE were assessed at baseline and Day 5, and percent change in mean values for each BoE was calculated. Biomarkers of potential harm (BoPH) linked to oxidative stress, platelet activation, and inflammation were also assessed. Levels decreased among subjects randomized to Vuse Solo versus Abstinence, respectively, for the following BoE: 42–96% versus 52–97% (non-nicotine constituents); 51% versus 55% (blood carboxyhemoglobin); and 29% versus 96% (nicotine exposure). Significant decreases were observed in three BoPH: leukotriene E4, 11-dehydro-thromboxane B2, and 2,3-dinor thromboxane B2 on Day 7 in the Vuse Solo and Abstinence groups. These findings show that ENDS use results in substantially reduced exposure to toxicants compared to smoking, which may lead to reduced biological effects.