Dosage compensation

A mechanism for regulating chromosome-wide gene expression based on the ratio of autosomes to sex chromosomes. In C. elegans, the hermaphrodite is XX with two X chromosomes while the male is X0 with only one X chromosome. Dosage compensation machinery in these nematodes reduces expression of genes on both X chromosomes in the hermaphrodite.

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.

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.

Male mating

Elaborate motor programs are characteristic of C. elegans male mating behavior. Driven by sensory perception males undergo a number of invariant steps allowing the male to locate, confront, and copulate with the hermaphrodite. Studies of C. elegans male mating have elucidated the cellular role of evolutionary conserved polycystins, which has further shed light on their human homologs in autosomal dominant polycystin kidney disease.

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.

Tail development

Development of the tail in C. elegans follows distinct sex-specific programs. Upon hatching there is very little morphological distinction between the hermaphrodite and the male C. elegans L1. By the adult stage, the hermaphrodite tail is a tapered whip of hypodermis. By contrast the adult male tale is a complex mating structure that stemmed from sex-specific cell lineages as well as reprogrammed cell fates.

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.

Asymmetric cell division

In C. elegans the three principal axes of the body (Anterio/Posterior, Dorsal/Ventral, and Left/Right) are established by a series of asymmetric cell division. It's through these types of division that cell determinants are unequally segregated into daughter cells resulting in the specification of cell fates. The first cell division in C. elegans, in the one-cell embryo, results in the establishment of the A/P axis.

Muscular system development and organization

The coordinated specification and functional assemblage of cells and tissues into the contractile organ system in the animal. C. elegans muscles are of two types: single sarcomere with focal attachment points at the ends (alimentary system and sex muscles) and obliquely striated muscles with many sarcomeres and no one substantial focal attachment point (body-wall muscles). Components of C. elegans muscles are similar to other animals and include heavy and light-chain myosin, actin, tropomyosin, troponin-like proteins, and paramyosin. Unlike other muscle systems, C. elegans muscles send neuron-like processes to neuropils that contain motor neuron axons rather than motor neurons sending axons to innervate the muscle. Contractile tissue is found throughout C. elegans and is required for locomotion (body wall muscle), eating (pharyngeal muscle), egg laying (vulval and uterine muscles, and gonad sheath), male mating (male tail muscles), and defecation (enteric muscles).

Quiescence

A reversible sleep-like state, characterized by inactivity, increased arousal threshold to elicit sensory responses, and homeostasis. In C. elegans these quiescent periods punctuate the start of each larval molt.