- RNA processing
After transcription in the nucleus and before translation into a protein in the cytoplasm, newly transcribed RNA undergoes post-transcriptional modifications to become the mature mRNA. These modifications include the addition of a 5'cap and 3'poly A tail, and splicing out of noncoding introns. These modifications are needed for the RNA molecule to be protected against RNase activity as well as for it to be recognized by molecules that mediate translation into proteins. Splicing of the RNA is required to remove the portions of the message that are not supposed to be translated into the final protein product. In addition to intron and exon splicing of the pre-mRNA, ~70% of pre-mRNAs in C. elegans are trans-spliced to one of two different splice leader sequences, SL1 or SL2.
- Glucose metabolism
Glucose metabolism refers to the biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates, which include glucose and its various forms such as the aldohexose glucohexose and D-glucose (dextrose), in living organisms. Glucose species molecules are an important source of energy for living organisms and is found free as well as combined in oligosaccharides and polysaccharides.Processes involving glucose metabolism is conserved in metazoans.
- Cell migration
Cell movement is an essential cell behavior for metazoan development. When this process is improperly orchestrated it can result in developmental disorders or pathologies such as tumor metastasis. In C. elegans, many cell types including canal associated neurons (CANs), hermaphrodite-specific neurons (HSNs), and Q neuroblasts migrate long distances during embryonic or larval development. Studies in C. elegans have elucidated many of the molecules required for stimulating and guiding the cell. These studies have shown that some directed movement rely on graded chemotactic signaling that is perceived by the cell and transduced to the cell's cytoskeleton. Chemotactic signaling molecules such as UNC-6, an extracellular matrix protein, can act as both an attractant, for cells expressing UNC-5, or as a repellant, for cells expressing UNC-40. Cell migration ultimately requires the regulation of cytoskeletal rearrangements. Studies have demonstrated UNC-73/Trio to be a main activator of Rac signaling in at least some of these migrating cells, which is proposed to drive such intracellular changes.
- RNA interference
RNA interference (RNAi) refers to the silencing of gene expression by the overexpression of RNA molecules. This process is associated with a cellular and nuclear defense mechanism used to combat molecular parasites such as transposons and viruses. In addition, RNA interference has been shown to play a regulatory role in development. Work in C. elegans and other organisms have identified many key regulators and pathways necessary for this process. Specifically, RNAi has been adapted into a tool for the study of gene function; through the use of RNAi, the expression of a target gene can be inhibited by the reverse engineering of a corresponding dsRNA.
- Feeding
Identification of and response to a potential food source is a life-critical process. C. elegans has proved to be a model organism for studying the molecular and cellular mechanisms involved in seeking a food source and discriminating its value. These studies have shown that C. elegans is capable of forming a memory of particular foods and is capable of modifying its eating behavior upon subsequent exposure to the familiar food. In addition, research has shown that this modification in behavior is mediated by extrinsic, such as C. elegans pheromone and bacterial molecules, and intrinsic chemical cues, such as serotonin levels. In C. elegans feeding can be observed by watching pharyngeal pumping, which is composed of a posterior-directed contraction of the grinder followed by an anterior-directed relaxation.
- Cuticle biogenesis
The C. elegans cuticle is a protective exoskeleton of specialized extracellular matrix (ECM) consisting primarily of collagen, lipids, and glycoproteins and is required for viability. (Chisholm and Hardin 2005; Page and Johnstone 2007). The cuticle determines the shape of the body and, through connection from the epidermis to muscle, provides anchoring points for muscle contraction. The cuticle also serves as a model for ECM formation and function with molecules and pathways involved in cuticle biogenesis conserved in vertebrates (Page and Johnstone 2007). The outer epithelial layer, the epidermis, of the embryo undergoes a series of cell fusions to make large multinucleate, or syncytial, epidermal cells, which secrete the materials needed to make up the cuticle. This protective layer is produced five times during C. elegans development, with each molt ending with an entirely new cuticle.
- Gene silencing
Inactivation of gene expression can occur at both the level of transcription and post-transcription. All silencing mechanisms are identical in that they require a small RNA species to provide the necessary gene sequence specificity and effector molecules that bind to the RNAs to process the RNA and to direct its inhibitory activity. Studies of these mechanisms in C. elegans has elucidated a number of different RNA-mediated post-transcriptional mechanisms. These mechanisms differ in the species of small RNAs involved. The different classes of small RNAs in C. elegans includes, microRNAs (miRNA), small interfering RNAs (siRNAs or rasi's), X-chromosome cluster RNAs (X-cluster), tiny noncoding RNAs (tncRNAs), and Piwi-associated RNAs (piRNAs). Gene silencing is accepted as a defense mechanism that evolved to protect the host from exogenous (foreign) sequence such as viral and transposon sequence. It has also been shown that gene silencing plays a critical role in endogenous gene expression to control the developmental timing of genes require for cell specificity, as well as playing a role in aging.
- Olfaction
Volatile organic molecules are sensed through olfaction. C. elegans can distinguish and respond to many volatile odorants through attractive or repulsive chemotactic behaviors. In some instances volatile compounds can induce both behaviors depending on its concentration. Olfaction studies in C. elegans has revealed a complex sensory system where only three types of neurons (AWC, AWA, and AWB) have been found to be responsible for processing over seven classes of volatile odorants, including alcohols, ketones, organic acids, sulfhydrals, and heterocyclic compounds. Detailed study of the molecular machinery behind odor reception has shown that each neuron controls a particular attractive or repulsive behavioral response, for example, AWC controls attractive chemotaxis responses and AWB controls repulsive chemotaxis responses. One distinguishing feature of C. elegans sensory system is that the sensory neurons are polymodal in their stimulus detecting ablility; that is, individual neurons in C. elegans express multiple odorant receptors allowing multiple sensory functions, whereas vertebrate neurons express a single receptor limiting their function to detecting a single odorant.
- Wnt signaling pathway
Wnt glycoproteins are signaling molecules that control a wide range of developmental processes and is a conserved feature of metazoan development. In C. elegans Wnt signaling has been shown to play a role in cell fate specification and determination of cell polarity, cell migration, and axis determination during axon outgrowth. A 'canonical' Wnt signaling pathway has been elucidated in vertebrate and invertebrate model systems where Wnt binding leads to the stabilization of the transcription factor beta-catenin, which then enters the nucleus to regulate Wnt pathway target genes. Like other species, the C. elegans genome encodes multiple genes for Wnt ligands, EGL-20, LIN-44, MOM-2, CWN-1, CWN-2) and Wnt receptors (LIN-17, MOM-5, MIG-1, CFZ-2, LIN-18). Canonical Wnt signaling in C. elegans, utilizes the beta-catenin BAR-1 to convert POP-1 into an activator and controls the expression of several homeobox genes. However, unlike vertebrates or Drosophila, the C. elegans genome encodes multiple beta-catenin genes (HMP-2, BAR-1, SYS-1, WRM-1), which give rise to noncanonical Wnt signalling pathways: for example, the endoderm induction pathway requires the beta-catenin WRM-1 and parallel input from a mitogen-activated kinase (MAPK) pathway to downregulate POP-1.