- 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).
- 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.
- Cuticle biogenesis
The C. elegans cuticle is a protective exoskeleton of specialized extracellular matrix (ECM) consisting primarily of collagen, lipids, and glycoproteins and is required for viability. (Chisholm and Hardin 2005; Page and Johnstone 2007). The cuticle determines the shape of the body and, through connection from the epidermis to muscle, provides anchoring points for muscle contraction. The cuticle also serves as a model for ECM formation and function with molecules and pathways involved in cuticle biogenesis conserved in vertebrates (Page and Johnstone 2007). The outer epithelial layer, the epidermis, of the embryo undergoes a series of cell fusions to make large multinucleate, or syncytial, epidermal cells, which secrete the materials needed to make up the cuticle. This protective layer is produced five times during C. elegans development, with each molt ending with an entirely new cuticle.
- 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.
- Sarcomere assembly
The sarcomere is the basic unit of a muscle cell and is comprised of thick and thin filaments made up of myosin and actin, respectively. Muscle sarcomere assembly involves many proteins and occurs in many steps, one of which is the attachment of sarcomeres to the sarcolemma (the membrane of the muscle cell). The steps involved in initiating the correct placement of sarcomere-sarcolemma attachments and other sarcomere substructures are poorly understood and are being addressed through studies of C. elegans mutants. These attachment sites are very similar to vertebrate adhesion complexes.
- Development
Development is the process of temporal and spatial control of gene expression that gives rise to a fully functional adult form of the organism. Studies of development in C. elegans have traced every cell from birth to final differentiated state in the developing nematode. These studies have elucidated cellular, genetic, and molecular mechanisms that control the division, growth, differentiation and morphogenesis of cells giving rise to tissues and organs in the nematode body. While most terminally differentiated cells can be traced by lineage back to a founder cell, there still remains a few cells types in the nematode with stochastic identity, relying on signals from the environment for their final identity.
- 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.
- Locomotion
The movement of the animal in relation to its environment requires coordinating an awareness of environmental cues with the firing of neuronal circuitry affecting the simultaneous contraction and relaxation of opposing muscle groups. C. elegans exhibits many types of movement, the two major types are crawling and swimming. Each of these movements have been further characterized by dominant body shapes, trajectories, angles, speeds, etc., peculiar to the movement. Fundamental to survival of the worm is the ability to sense and move towards or away from different stimuli. Forward and backwards movements can be induced in the lab through the stimulation of the mechanosensory neural network.
- Germline immortality
In contrast to somatic cells, which exist for only one generation, germ cells proliferate through successive generations. These cells are maintained through a microenvironment, referred to as a stem cell niche, which maintains mitotic-arrested cells. The proliferative fate of these stem cells are controlled in these niches through cellular architecture and secreted factors. In C. elegans, the equivalent of the stem cell niche for the immortal germline cells is provided by the distal tip cell (DTC) and its gonad arm processes. Germ line DNA-damage checkpoints are key monitors of processes involved in germ cell immortality.
- Germline development
During germline development germ cells, or reproductive cells, are specified, proliferated, and maintained for the establishment of a germline in the next generation. In C. elegans, germ cells are specified from somatic cells during early embryogenesis. During larval stages, cells of the germline proliferate, undergo meiotic entry, and the germline undergoes sex determination. Gametogenesis, specifically spermatogenesis, begins in late L4 in the hermaphrodite, and switches to oogenesis after the adult molt. Germline proliferation, meiotic development, and gametogenesis continue throughout adulthood.