Six innexins contribute to electrical coupling of C. elegans body-wall muscle.

C. elegans body-wall muscle cells are electrically coupled through gap junctions. Previous studies suggest that UNC-9 is an important, but not the only, innexin mediating the electrical coupling. Here we analyzed junctional current (I j ) for mutants of additional innexins to identify the remaining innexin(s) important to the coupling. The results suggest that a total of six innexins contribute to the coupling, including UNC-9, INX-1, INX-10, INX-11, INX-16, and INX-18. The I j deficiency in each mutant was rescued completely by expressing the corresponding wild-type innexin specifically in muscle, suggesting that the innexins function cell-autonomously. Comparisons of I j between various single, double, and triple mutants suggest that the six innexins probably form two distinct populations of gap junctions with one population consisting of UNC-9 and INX-18 and the other consisting of the remaining four innexins. Consistent with their roles in muscle electrical coupling, five of the six innexins showed punctate localization at muscle intercellular junctions when expressed as GFP- or epitope-tagged proteins, and muscle expression was detected for four of them when assessed by expressing GFP under the control of innexin promoters. The results may serve as a solid foundation for further explorations of structural and functional properties of gap junctions in C. elegans body-wall muscle.

High resolution map of Caenorhabditis elegans gap junction proteins.

The innexin family of gap junction proteins has 25 members in Caenorhabditis elegans. Here, we describe the first high-resolution expression map of all members through analysis of live worms transformed with green fluorescent protein under the control of entire promoter regions. Our analyses show that innexins have dynamic expression patterns throughout development and are found in virtually all cell types and tissues. Complex tissues, such as the pharynx, intestine, gonad, as well as scaffolding tissues and guidepost cells express a variety of innexins in overlapping or complementary patterns, suggesting they may form heteromeric and heterotypic channels. Innexin expression occurs in several types of cells that are not known to form gap junctions as well as in a pair of migrating cells, suggesting they may have hemichannel function. Therefore, innexins likely play roles in almost all body functions, including embryonic development, cell fate determination, oogenesis, egg laying, pharyngeal pumping, excretion, and locomotion.

Neuronal and intestinal protein kinase d isoforms mediate Na+ (salt taste)-induced learning.

Ubiquitously expressed protein kinase D (PKD) isoforms are poised to disseminate signals carried by diacylglycerol (DAG). However, the in vivo regulation and functions of PKDs are poorly understood. We show that the Caenorhabditis elegans gene, dkf-2, encodes not just DKF-2A, but also a second previously unknown isoform, DKF-2B. Whereas DKF-2A is present mainly in intestine, we show that DKF-2B is found in neurons. Characterization of dkf-2 null mutants and transgenic animals expressing DKF-2B, DKF-2A, or both isoforms revealed that PKDs couple DAG signals to regulation of sodium ion (Na+)-induced learning. EGL-8 (a phospholipase Cbeta4 homolog) and TPA-1 (a protein kinase Cdelta homolog) are upstream regulators of DKF-2 isoforms in vivo. Thus, pathways containing EGL-8-TPA-1-DKF-2 enable learning and behavioral plasticity by receiving, transmitting, and cooperatively integrating environmental signals targeted to both neurons and intestine.