Vulval development

The C. elegans vulva connects the hermaphrodite uterus to the outside of the nematode. The development of this organ is an intensively studied biological process making it a useful model for animal organogenesis. C. elegans vulval development involves the temporal and spatial coordination of intercellular signaling, evolutionarily conserved signal transduction pathways, and transcriptional regulation. Among the pathways involved in vulval development are the WNT, epidermal growth factor (EGF), and LIN-12/NOTCH signaling pathways. These pathways work in temporal succession to prime epidermal cells to first be competent to take on vulva cell fates and later to solidify their vulval cell specification. These pathways also work antagonistically to specify the precise pattern of cell fates needed to form the vulva. A key cell in vulval development is the anchor cell. Signals from this cell initiate the transition from epidermal to vulval precursor cell. This cell also influences the specification of surrounding uterine cells, which is required to connect the uterus to the vulva. The development of the final vulval organ requires the anchor cell to invade between terminally differentiated vulval cells in a behavior analogous to that of metastatic tumor cells.

Response to pathogens

C. elegans is susceptible to disease or death brought on by a number of different microbial or fungal pathogens. While some of these pathogens, e.g., Drechmeria conispora and Microbacterium nematophilum are more specific to nematodes, other pathogens, e.g., Pseudomonas aeruginosa, Salmonella enterica, etc., are also pathogenic to humans. Genetic studies of C. elegans response to these pathogens have shown the nematode to employ three main mechanisms to defend against pathogen attack. First, as a behavioral response, C. elegans has been shown to use olfactory cues to distinguish different bacteria and respond with avoidance to those that are deemed harmful. Second, C. elegans has evolved physical barriers to infection that include a cuticle of collagen and chitin that protects the worm from its environment. This cuticle is also replaced at each larval molt, decreasing the worm's exposure to harmful bacteria that may be hitching a ride. In addition, C. elegans has evolved a pharyngeal grinder capable of pulverizing bacteria, keeping live bacteria from entering the gut. Third, C. elegans nematodes have inducible innate immune responses that are analogous to stress response pathways present in other organisms, for example, the PMK-1/P38 MAPK signaling pathway induced in response to Salmonella enterica.

Larval development

During post-embryonic development the temporal and spatial regulation of cellular and molecular mechanisms continue past embryogenesis to give rise to a fully functional adult. Post-embryonic development in C. elegans involves progression of the animal through four larval stages. Post-embryonic development involves further limited somatic cell division and cell death to bring the final total to 959 somatic nuclei in the hermaphrodite and 1031 in the male. Other remarkable processes during this period include cell migrations, neuronal rewiring, and adoption of final cell fates. Under conditions of stress, e.g., starvation, reproductive development ceases and the animal switch to a physiologically distinct developmental program to produce the dauer larva.

Sensory perception

The series of events required for an organism to receive a sensory stimulus, convert it to a molecular signal, and recognize and characterize the signal. This is a neurological process.

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.

DNA damage response

DNA damage can occur during normal recombination events or result from various insults, such as exposure to chemical mutagens or exposure to radiation. Metazoans have evolved mechanisms to detect, assess, and deal with any damage at specific checkpoints during the cell cycle. Studies in yeasts and mammals have identified several genes that are required for proper activation of cell cycle check-points following various types of DNA damage. However, in these metazoans, DNA damage can induce apoptosis as well. The inability to efficiently repair DNA damage or remove cells with severely damaged genomes has been linked to several human cancers.

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.

Recombination

The process in which genetic material is exchanged, either between different chromosomes or different regions between the same chromosome, to result in a combination of genetic material different from the starting genotypes. Defects in recombination processes can lead to alterations in the proper segregation of genetic material to daughter nuclei. In C. elegans the rate of recombination was shown to be inversely affected by hermaphrodite age and temperature. Recombination rates decrease with age of the hermaphrodite and increase with temperature.

Response to stress

A stress response is any physical response to factors that upset the normal balance of a biological event. C. elegans nematodes are susceptible to many different environmental stressors that include changes in temperatures, exposure to high osmolarity, and changes in oxygen levels. Internal stressors include DNA damage, accumulation of unfolded proteins, and accumulation of reactive oxygen species. These stressors have been shown to have a strong impact on the lifespan of C. elegans. The regulation of stress responses in the worm are similar to that in other organisms and include modulations of pathways that control caloric intake, mitochondrial respiration, insulin/IGF-1 (IIS), and JNK (c-Jun N-terminal kinase) signaling.

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.