Thermotaxis

The directed movement of an organism in response to a temperature gradient. Movement may be towards either a higher or lower temperature.

Gap junction biogenesis and organization

Gap junctions, along with chemical synapses, mediate communication between neurons. Innexins are major components of these junctions. Gap junctions can be identified in electron micrographs as parallel membranes of closely apposed cells.

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.

Synaptogenesis

The formation of the chemical synaptic junction that mediates communication between neurons and other neurons or muscle cells. These junctions can be identified in electron micrographs as darkened specialized areas on the presynaptic side of the junction that contains clusters of synaptic vesicles.

Response to toxicity

Exposure to a toxic substance can activate any number of processes that result in a change in state or activity of the organism. As a soil dwelling organism, C. elegans has evolved defenses against damaging substances in the soil environment and as such has proved to be an ideal organism for studying biological responses to toxins. These responses can occur at an organism level, such as invoking an avoidance behavior, or on a cellular level, such as activation of a cellular stress response. Cellular defenses have been shown to be invoked in response to reactive oxygen species, heavy metals, and toxin-induced unfolded proteins.

Signal transduction

Signal transduction begins with a stimulating event, such as a ligand binding to a receptor on the surface of the cell, and is followed by intracellular signaling steps that eventually trigger a response. In many cases the end response is modification of the regulation of gene transcription, but could also be the regulation of a metabolic process.

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.

Defecation

In C. elegans the expulsion of intestinal contents occurs every 45-50 seconds. This cycle is characterized by a pattern of muscle contractions under both muscle and neuronal control. The steps of the defecation cycle are a posterior body contraction (pBoc), an anterior body contraction (aBoc), and the final expulsion step (Exp) where the enteric muscles contract, opening the anus and allowing the intestinal contents to be released. Each step is independently controlled as mutations exist that affect one step but do not alter the timing or occurrence of the other. Further, Ca++ oscillations in the intestine, rather than neuronal stimulation, have been shown to control the initiating pBoc step. The contractions of the enteric muscles are controlled by GABA motor neurons AVL and DVB through an excitatory GABA-gated cation channel. The periodicity of the cycle is influenced by the presence of food, is temperature compensated, and can be reset by mechanosensory input.

Hormesis

The process whereby a low exposure to a toxin or stressor produces a generally positive response in the animal that is the opposite effect produced in response to a higher exposure. This can be observed in cases where C. elegans is exposed to short doses of temperature stress during development. Under such limited exposures, animals exhibit a longer life span than animals reared at room temperature. However, extended exposure to thermal stress results in severely shortened lifespans.

Mitosis

Mitosis is part of the eukaryotic cell cycle and results in the production of two daughter cells each with a copy of the genome. The cell cycle itself is comprised of an interphase (made up of three stages G1, S, and G2) and the M (mitotic) phase. Cell growth, active transcription and translation, and DNA replication occur during interphase. During M phase duplicated DNA (chromatin) condense into sister chromatids (prophase); the nuclear envelop breaks down, kinetochore microtubles attach to the chromosomes and centrosomes are pushed to the poles of the growing spindle (prometaphase); the chromosomes are lined up on the metaphase plate (metaphase); sister chromatids are pulled to spindle poles at opposite ends of the cell (anaphase); the nuclear envelop is reformed and the chromatids decondense to chromatin (telophase); and the cell is cleaved into two by a contractile ring and the resolution of a cleavage furrow (cytokinesis). In some variant cell cycles nuclear division may not be followed by cell division, or G1 and G2 phases may be absent.