- 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.
- Mitochondrial DNA maintenance and expression
The mitochondrial genome is a vital component of animal metabolism, physiology, and development. C. elegans mitochondrial DNA (mtDNA) is typical of animal mitochondrial genomes in its size, 13,794 nucleotides in length, and gene content of 32 genes: 2 ribosomal RNAs, 22 transfer RNAs, and 12 protein subunits of the mitochondrial respiratory chain (MRC). Unlike nuclear DNA, mtDNA is maternally inherited and can be present at tens to tens of thousands of copies per cell. Its copy number is developmentally regulated, with mtDNA increasing about 30-fold between the L1 and the adult stages. Blocking mtDNA increase leads to larval arrest. Underlying its essential role in the biology of C. elegans, over 200 nuclear genes are needed to replicate, transcribe, and maintain the mitochondrial genome and to assemble the translation machinery required for expressing mitochondrial proteins. Disruptions in these processes have shown that the mitochondrion plays a critical role in aging, life span determination, reactive oxygen species response, the unfolded protein response, and apoptosis. Oddly, despite the essential role of mtDNA encoded genes in the cellular and organismal biology of C. elegans, mutations in mtDNA have not been reported. By contrast, over 300 lesions in human mtDNA have been described, many associated with neurological, endocrinological or muscle diseases.
- P granule biogenesis and organization
Germ granule proteins are found among a wide variety of species. In C. elegans, these granules are known as P granules. They are initially seen in the cytoplasm of oocytes and early embryos. In early embryogenesis they are asymmetrically segregated into blastomeres that eventually give rise to the germ line. In adults, P granules are peri-nuclear and cluster with nuclear pore complexes. They are associated with RNA metabolism and appear to play a role in nascent mRNA release from the nucleus.
- Intestine development
The C. elegans intestine is attached to the posterior pharynx and extends the length of the worm, ending at the rectum. This major organ of the worm consists of 20 large, polyploid epithelial cells arranged in pairs, forming a tube. The intestine is responsible for food digestion, nutrient absorption, and synthesizing and storing macromomlecules such as fat droplets and birefringent gut granules. The intestine also plays major roles in the rhythmic behavior of the defecation cycle as well as stress responses and lifespan.
- 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.
- Post-transcriptional RNA binding
Post-transcriptional control of RNA metabolism plays a major role in development and involves proteins that bind to RNA (RBPs). RBP binding has been shown to display tissue-specific activity, which when altered can result in tissue-specific mutant phenotypes. Molecular studies have identified many RBPs that bind regulatory sequences in the 3' untranslated regions of mRNAs. Studies of RBPs in C. elegans seek to provide insights into how RBPs exert coordinate control of their RNA targets and affect development.
- Egg laying
C. elegans hermaphrodites exhibit a periodicity in the rate and temporal pattern of egg-laying. Egg laying is modulated by diverse environmental cues. Egg laying behavior has served as an important phenotypic assay for the genetic dissection of neuronal signal transduction mechanisms. Studies in C. elegans have elucidated the roles of specific neurons in the egg-laying motor circuit, which release multiple neurotransmitters affecting distinct parameters of egg-laying muscle activity, and the possible mechanisms for sensory control of egg-laying behavior.
- 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.
- Corpse engulfment
Cell corpses are removed through phagocytosis as a final step of apoptosis. The removal of these corpses protects the organism from harmful contents that may be released from the dying cell. Cell corpse removal requires properly identifying, ingesting and degrading the dying cell. During this process the engulfing cell undergoes cytoskeletal reorganization to send a projection towards the apoptotic cell. Over a dozen genes have been identified in C. elegans that play a role in apoptosis, with many of them, including
ced-12,
ced-10,
ced-5, and
ced-2, being required for this final cell corpse engulfment step.
- Innate immune response
The innate immune system is the first line of cellular defense in all classes of plants and animals against infection by other organisms. A number of signaling pathways in the nematode have been identified that act in this host response to microbial and fungal pathogens. Like other invertebrates, C. elegans does not have an adaptive immune system. However, unlike some invertebrates, C. elegans does not have any specialized cells dedicated to immune function. Triggering of the innate immune cellular response can occur in any tissue of the worm, and utilizes the any number of signaling pathways, which normally play roles in cell signaling events used during development or normal cell homeostasis.