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).
RTK/Ras/MAPK signaling pathway
Receptor Tyrosine Kinase (RTK)/Ras GTPase/MAP kinase (MAPK) activated signaling pathways are used repeatedly during metazoan development to control many different biological processes. C. elegans contains two different RTKs (LET-23/EGFR and EGL-15 /FGFR) that are known to stimulate LET-60/Ras and a MAPK cascade consisting of the kinases LIN-45/Raf, MEK-2/MEK and MPK-1/ERK. This Ras/MAPK cascade is required for multiple developmental events, including induction of vulval, uterine, spicule, P12 and excretory duct cell fates, control of sex myoblast migration and axon guidance, and promotion of germline meiosis. Studies in C. elegans have provided much insight into the basic framework of this RTK/Ras/MAPK signaling pathway, its regulation, how it elicits cell-type specific responses, and how it interacts with other signaling pathways such as the Wnt and Notch pathways.
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.