DRE-1: An Evolutionarily Conserved F Box Protein that Regulates C. elegans Developmental Age

Protein arginine methylation in mammals: who, what, and why

The covalent marking of proteins by methyl group addition to arginine residues can promote their recognition by binding partners or can modulate their biological activity. A small family of gene products that catalyze such methylation reactions in eukaryotes (PRMTs) works in conjunction with a changing cast of associated subunits to recognize distinct cellular substrates. These reactions display many of the attributes of reversible covalent modifications such as protein phosphorylation or protein lysine methylation; however, it is unclear to what extent protein arginine demethylation occurs. Physiological roles for protein arginine methylation have been established in signal transduction, mRNA splicing, transcriptional control, DNA repair, and protein translocation.

Kinetic mechanism of protein arginine methyltransferase 1

Protein arginine methyltransferases (PRMTs) are SAM-dependent enzymes that catalyze the mono- and dimethylation of peptidyl arginine residues. Although all PRMTs produce monomethyl arginine (MMA), type 1 PRMTs go on to form asymmetrically dimethylated arginine (ADMA), while type 2 enzymes form symmetrically dimethylated arginine (SDMA). PRMT1 is the major type 1 PRMT in vivo, thus it is the primary producer of the competitive NOS inhibitor, ADMA. Hence, potent inhibitors, which are highly selective for this particular isozyme, could serve as excellent therapeutics for heart disease. However, the design of such inhibitors is impeded by a lack of information regarding this enzyme's kinetic and catalytic mechanisms. Herein we report an analysis of the kinetic mechanism of human PRMT1 using both an unmethylated and a monomethylated substrate peptide based on the N-terminus of histone H4. The results of initial velocity and product and dead-end inhibition experiments indicate that PRMT1 utilizes a rapid equilibrium random mechanism with the formation of dead-end EAP and EBQ complexes. This mechanism is gratifyingly consistent with previous results demonstrating that PRMT1 catalyzes substrate dimethylation in a partially processive manner.

C. elegans dauer formation and the molecular basis of plasticity

Because life is often unpredictable, dynamic, and complex, all animals have evolved remarkable abilities to cope with changes in their external environment and internal physiology. This regulatory plasticity leads to shifts in behavior and metabolism, as well as to changes in development, growth, and reproduction, which is thought to improve the chances of survival and reproductive success. In favorable environments, the nematode Caenorhabditis elegans develops rapidly to reproductive maturity, but in adverse environments, animals arrest at the dauer diapause, a long-lived stress resistant stage. A molecular and genetic analysis of dauer formation has revealed key insights into how sensory and dietary cues are coupled to conserved endocrine pathways, including insulin/IGF, TGF-beta, serotonergic, and steroid hormone signal transduction, which govern the choice between reproduction and survival. These and other pathways reveal a molecular basis for metazoan plasticity in response to extrinsic and intrinsic signals.

Caenorhabditis elegans nuclear receptors: insights into life traits

Nuclear receptors are a class of hormone-gated transcription factors found in metazoans that regulate global changes in gene expression when bound to their cognate ligands. Despite species diversification, nuclear receptors function similarly across taxa, having fundamental roles in detecting intrinsic and environmental signals, and subsequently in coordinating transcriptional cascades that direct reproduction, development, metabolism and homeostasis. These endocrine receptors function in vivo in part as molecular switches and timers that regulate transcriptional cascades. Several Caenorhabditis elegans nuclear receptors integrate intrinsic and extrinsic signals to regulate the dauer diapause and longevity, molting, and heterochronic circuits of development, and are comparable to similar in vivo endocrine regulated processes in other animals.

Cell fusion in Caenorhabditis elegans

In the nematode Caenorhabditis elegans, 300 of the 959 somatic nuclei present in the adult hermaphrodite are located in syncytia. These syncytia are formed by the fusion of mononucleate cells throughout embryonic and postembryonic development. These cell fusions occur in a well-characterized stereotypical pattern, allowing investigators to study many cell fusion events at the molecular and cellular levels. Using tools that allow visualization of cell membranes, cell junctions, and cell cytoplasm during fusion, genetic screens have identified many C. elegans cell fusion genes, including those that regulate the fusion cell fate decision and two genes that encode components of the cell fusion machinery.

C. elegans Aging: Proteolysis Cuts Both Ways

Recent reports from two laboratories working on the nematode Caenorhabditis elegans have identified both positive and negative roles for ubiquitin-mediated proteolysis in the regulation of longevity by the insulin/insulin-like growth factor signaling pathway.