In C. elegans dwelling and roaming activities are two examples of distinctive behaviors. During the dwelling phase worms have an intermittent backward and forward movement and present a low/high speed of locomotion. However throughout the roaming phase worms have predominantly high speed forward movement with few changes of direction (Fujiwara et al., 2002; Shtonda and Avery, 2006). These two different behaviors are controlled by the presence or absence of food in the environment (Fujiwara et al., 2002). Both states seem to be regulated in a different way, thus while dwelling is induced by internal metabolic perceptions, roaming is mediated by stimuli detected via the amphid neurons (Ben Arous et al., 2009).

Fig. 1 shows that the roaming behavior of nrx-1–deficient mutants was almost annulled when worms were transferred from OP50 bacteria plates to plate without food. This contrasts with the behavior of N2 wild type strain. Interestingly, transgenic expression in the nrx-1 deficient mutant of cDNAs coding human alpha-NRXN-1 or beta-NRXN-1, all driven by the C. elegans nrx-1 promoter, rescued the mutant phenotype of the nematode (Fig. 1). In these experiments nrx-1(tm1961) transgenic animal expressing beta-NRX-1 from the nematode were used as control. To quantify the exploratory capacity of the worms, twenty L4 larval stage animals of each genotype grown on OP50 E. coli in fresh NGM plates were picked and placed in the middle of a 9 cm plate containing 8 ml of agar medium (2% agar, 0.25% v/v Tween 20, 10 mM HEPES pH 7.2) without bacteria. Plates were incubated from 5 to 7 days at 20 ºC. The fingerprints of the worms were recognized by sight as a consequence of their roaming, and they were quantified by scanning the surface of agar dishes at 600-ppp resolution and analyzing the images in “Image J” software using custom scripts. Images were turned into binary format converting them through a predetermined threshold, and finally a particles analysis was performed. Data was normalized with respect N2 wild-type strain.

A previous report had shown that human and rat neuroligin-1 were functional in C. elegans (Calahorro and Ruiz-Rubio, 2012). Together, these results suggest that the functional mechanism underpinning both neuroligin and neurexin in the nematode are comparable to human. In this sense the nematode might constitute a simple in vivo model for understanding basic mechanisms involved in some neurological diseases.

Caenorhabditis elegans is becoming an important model in pharmacology and toxicology (Leung et al., 2008), but there is little biochemical information regarding its xenobiotic metabolic capacity. The current study investigated the in vivo activity of C. elegans with two human cytochrome P450 (CYP) substrates, phenacetin and testosterone, which are metabolized by human CYP1A2 and CYP3A enzymes, respectively, into acetamidophenol and 6β-hydroxytestosterone via deethylation and hydroxylation reactions.

Each experiment included (a) 50 ml liquid cultures with 30 µM substrate, a mixed-stage N2 (Bristol) population, and OP50 bacteria in S medium; (b) N2 cultures without OP50; (c) OP50 cultures without N2;, and (d) substrate-only controls. All cultures were done in triplicate and incubated on a shaker at 20 °C for 24 hr. OP50 and C. elegans were isolated afterward using centrifugation and sucrose flotation, respectively. The resultant extract was homogenized using sonication and resuspended in 1.5 ml 0.1 N NaCl solution. The culture medium and homogenate were analyzed for substrates and metabolites using HPLC-MS/MS (Micromass Quattro Ultima, Beverly, MA) and published methods (Walsky and Obach, 2004).

C. elegans generated the human CYP3A diagnostic metabolite 6β-hydroxytestosterone in liquid culture with or without OP50 (Table 1). The medium concentration of testosterone in the N2 cultures was nearly eliminated after 24 hr, but was unchanged in both substrate controls and OP50 cultures. This indicated that C. elegans either metabolized or bioconcentrated testosterone. 6β-hydroxytestosterone was detected in the N2 homogenate, demonstrating human CYP3A-like metabolism.

The results of the phenacetin experiment were less clear-cut. The medium concentration of phenacetin in the N2 cultures but not the OP50-only cultures was reduced after 24 hr incubation, but acetamidophenol was never detected at levels exceeding 0.04 µM in any culture medium or homogenate (Table 1). This is likely to result from further metabolism to chemical forms that we did not measure, but testing this hypothesis will require additional experiments.

The current findings suggest that C. elegans possessed human CYP3A-like activities, consistent with previous evidence for a functional role of human CYP3 homologs in C. elegans genome (Leung et al., 2010). However, the finding of modest CYP1A2-like activity was surprising based on previous work (Leung et al., 2010). Clearly further experiments are needed to explore how C. elegans metabolizes pharmaceuticals and toxicants (Kosel et al., 2011; Shäfer et al., 2009).

Diets rich in omega-3 fatty acids are associated with health benefits in humans. C. elegans can synthesize all polyunsaturated fatty acids de novo and thus serves as an excellent genetic system for the determining the fundamental roles of these fatty acids in development and physiology. De novo synthesis of omega-3 fatty acids in C. elegans requires the activities of a delta-12 desaturase (FAT-2) and an omega-3 desaturase FAT-1, both of which are desaturases that are not present in humans or other mammals (Watts and Browse, 2002). The RB969 strain contains the ok873 allele, which was reported to contain a 1224 base pair deletion of DNA within the fat-2 gene. We performed gas chromatography analysis to determine the fatty acid composition of the RB969 strain. Based on previous analysis of the fat-2(wa17) allele, we expected to observe a loss of 20-carbon polyunsaturated fatty acids (PUFAs). However, we were surprised to find that the RB969 strain contained a higher abundance of PUFAs than wild type, with an increased abundance of omega-3 (n-3) PUFAs (Table 1). PCR analysis of the RB969 strain showed amplification of the expected deletion product, but also amplification of larger bands, including one corresponding to the wild type fat-2 gene. After backcrossing the strain 8 times, we were unable to obtain segregants that contained only the wild type or only the fat-2 deletion PCR products. Therefore, we hypothesized that in addition to a deletion of genomic DNA in the fat-2 gene, this genomic region may have undergone a duplication event, such that both copies of chromosome IV in RB969 worms contained a wild type as well as a deleted version of the fat-2 gene.