By contrast, tagging NLF-1 with HDEL, a known ER-retention signal ( Basham and Rose, 2001; Denecke et al., 1992; Semenza et al., 1990) did not alter its ER localization (
Figure 2A, HDEL) or affect its rescuing ability ( Figure S2F). Therefore, NLF-1’s ER localization is critical for its function. Collectively, these data indicate that NLF-1 is a novel ER resident protein that functions in the same biological process as the NCA channel. To determine the physiological deficit that underlies the fainting phenotype shared by nlf-1 and nca mutants, we first identified the minimal neural network that contributes most critically to this movement deficit. While NLF-1 is expressed in sensory neurons, interneurons ( Figure 2E) and excitatory motor neurons ( Figure S2G), the restored expression of NLF-1 in the premotor interneurons, see more a subset of interneurons that input directly onto the motor neurons, was necessary to restore the initiation and continuity of rhythmic locomotion in nlf-1 mutants ( Figures 3A, 3B, and S3B; Pnmr-1+Psra-11), and to prevent frequent halting ( Figure S3A; Pnmr-1+Psra-11). By contrast, restoring the NLF-1 expression in motor neurons did not rescue fainting ( Figures 3A, 3B, S3A, and S3B; Pacr-5+Punc-4). Similarly, the locomotion defect of unc-79 fainters was only rescued by restoring their expression in premotor interneurons, not in motor neurons
(data not shown). These results point to dysfunctional premotor interneurons, rather than a lack of motor activity, being the primary cause of the failure in the initiation and maintenance of rhythmic Adriamycin datasheet locomotion exhibited by fainters. Among all premotor interneurons, restoring NLF-1 expression in a subgroup, Oxalosuccinic acid including AVA and AVE, led to the most significant, partial rescue of fainting (Figures 3A, 3B, and S3B; Pnmr-1). Through real-time calcium imaging, we recently demonstrated that the AVA and AVE premotor interneurons exhibit similar activity profiles during spontaneous movements ( Kawano et al., 2011). In wild-type animals, coimaged AVA and AVE exhibited large and periodic rise in intracellular
Ca2+ that temporally correlated with the initiation and duration of backing ( Kawano et al., 2011; Figures 3C and 3D). In both nca(lf) and nlf-1 mutants, pulses of Ca2+ transients in AVA and AVE exhibited a significantly reduced amplitude ( Figures 3C and 3D), which corresponded with shorter backing, and indicates a reduced premotor interneuron activity. Restoring NLF-1 expression only in these neurons fully restored the Ca2+ transient profile ( Figures 3C and 3D). These transgenic animals exhibited Ca2+ transients that were slightly higher than wild-type animals ( Figure 3D), which may be caused by NLF-1 overexpression. These results imply that NLF-1 and the NCA channel potentiate premotor interneurons, whose activity is most critical to maintain the continuity of locomotion.