Reproduction
A fundamental biological process resulting in the production of offspring. In C. elegans, reproduction can result from self-fertilization within a hermaphrodite or by fertilization by mating of a male and hermaphrodite. In C. elegans, during the fourth larval stage of hermaphrodite development, the germline undergoes spermatogenesis to make functional sperm that are stored in the the gonad. In the adult stage, the germline ceases spermatogenesis and switches to oogenesis to produce oocytes that are fertilized by the previously generated spermatozoa or by spermatozoa deposited into the spermatheca during mating with a male. The embryos produced by self-fertilization are encased in an eggshell and initiate development within the uterus of the hermaphrodite. When they reach about the 30-cell stage, the egg-embryos are laid by the hermaphrodite through a vulva.
Mechanosensation
Mechanosensation converts mechanical energy into electrical signals allowing an organism to use physical cues from the environment or from internal sensors to affect its behavior. Mechanical stimuli are received through mechanosensory receptor neurons (MRNs). In C. elegans, there are 30 putative MRNs in hermaphrodites while an additional 52 MRNs are found in males. More than 40 of these male-specific MRNs are found in the male tail, hook, post-cloacal sensilla and spicule and are required for male mating. MRNs transmit electrical signals to other neurons through electrical or chemical synapses. MRNs may or may not have ciliated dendrite endings, which is some cases are exposed to the outside. Mechanical stimuli initiate as well as modulate many behaviors of the worm. MRNs allow the worm to respond to light touch, such as stroking with an eyelash as well as harsh touch, such as prodding with a pick.
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.