Fibroblast growth factors (FGFs) regulate many important developmental and homeostatic physiological events. The FGF superfamily contains several families. In this review, we present recent findings on the two FGFs of the nematode Caenorhabditis elegans from both functional and phylogenic points of view. C. elegans has a single FGFR (EGL-15) with two functionally exclusive isoforms, and two FGFs (LET-756 and EGL-17), which play distinct roles: an essential function for the former, and guidance of the migrating sex myoblasts for the latter. Regulation of homeostasis by control of the fluid balance could be the basis for the essential function of LET-756. Phylogenetic and functional studies suggest that LET-756, like vertebrate FGF9, -16, and -20, belongs to the FGF9 family, whereas EGL-17, like vertebrate FGF8, -17, and -18, could be included in the FGF8 family.
Heterotrimeric G proteins, composed of alpha , beta , and gamma subunits, are able to transduce signals from membrane receptors to a wide variety of intracellular effectors. In this role, G proteins effectively function as dimers since the signal is communicated either by the G alpha subunit or the stable G betagamma complex. When inactive, G alpha -GDP associates with G betagamma and the cytoplasmic portion of the receptor. Ligand activation of the receptor stimulates an exchange of GTP for GDP resulting in the active signaling molecules G alpha -GTP and free G betagamma , either of which can interact with effectors. Hydrolysis of GTP restores G alpha -GDP, which then reassociates with G betagamma and receptor to terminate signaling. The rate of G protein activation can be enhanced by the guanine-nucleotide exchange factor, RIC-8 , while the rate of GTP hydrolysis can be enhanced by RGS proteins such as EGL-10 and EAT-16 . Evidence for a receptor-independent G-protein-signaling pathway has been demonstrated in C. elegans early embryogenesis. In this pathway, the G alpha subunits GOA-1 and GPA-16 are apparently activated by the non-transmembrane proteins GPR-1 , GPR-2 , and RIC-8 , and negatively regulated by RGS-7 . The C. elegans genome encodes 21 G alpha , 2 G beta and 2 G gamma subunits. The alpha subunits include one ortholog of each mammalian G alpha family: GSA-1 (Gs), GOA-1 (Gi/o), EGL-30 (Gq) and GPA-12 (G12). The remaining C. elegans alpha subunits ( GPA-1 , GPA-2 , GPA-3 , GPA-4 , GPA-5 , GPA-6 , GPA-7 , GPA-8 , GPA-9 , GPA-10 , GPA-11 , GPA-13 , GPA-14 , GPA-15 , GPA-16 , GPA-17 and ODR-3 ) are most similar to the Gi/o family, but do not share sufficient homology to allow classification. The conserved G alpha subunits, with the exception of GPA-12 , are expressed broadly while 14 of the new G alpha genes are expressed in subsets of chemosensory neurons. Consistent with their expression patterns, the conserved C. elegans alpha subunits, GSA-1 , GOA-1 and EGL-30 are involved in diverse and fundamental aspects of development and behavior. GOA-1 acts redundantly with GPA-16 in positioning of the mitotic spindle in early embryos. EGL-30 and GSA-1 are required for viability starting from the first larval stage. In addition to their roles in development and behaviors such as egg laying and locomotion, the EGL-30 , GSA-1 and GOA-1 pathways interact in a network to regulate acetylcholine release by the ventral cord motor neurons. EGL-30 provides the core signals for vesicle release, GOA-1 negatively regulates the EGL-30 pathway, and GSA-1 modulates this pathway, perhaps by providing positional cues. Constitutively activated GPA-12 affects pharyngeal pumping. The G alpha subunits unique to C. elegans are primarily involved in chemosensation. The G beta subunit, GPB-1 , as well as the G gamma subunit, GPC-2 , appear to function along with the alpha subunits in the classic G protein heterotrimer. The remaining G beta subunit, GPB-2 , is thought to regulate the function of certain RGS proteins, while the remaining G gamma subunit, GPC-1 , has a restricted role in chemosensation. The functional difference for most G protein pathways in C. elegans, therefore, resides in the alpha subunit. Many cells in C. elegans express multiple G alpha subunits, and multiple G protein pathways are known to function in specific cell types. For example, Go, Gq and Gs-mediated signaling occurs in the ventral cord motor neurons. Similarly, certain amphid neurons use multiple G protein pathways to both positively and negatively regulate chemosensation. C. elegans thus provides a powerful model for the study of interactions between and regulation of G protein signaling.
Curr Opin Cell Biol,
In Caenorhabditis elegans, cell migration is guided by localized cues, including molecules such as EGL-17/FGF and UNC-6/netrin. These external cues are linked to an intracellular response to migrate, at least in part, by CED-5, a homolog of DOCK180/MBC, and MIG-2, a Rac-like GTPase. In addition, metalloproteases are required for a cell migration that controls organ shape.
J Cell Physiol,
Pumilio and FBF (PUF) proteins are conserved stem cell regulators that maintain germline stem cells (GSCs) in worms and flies. Moreover, they are also present in vertebrate stem cells. The nematode Caenorhabditis elegans has multiple PUF proteins with specialized roles. Among them, PUF-8 protein controls multiple cellular processes, including proliferation, differentiation, sperm-oocyte decision, and cell fate reprogramming, depending on the genetic context in the C. elegans germline. In this review, we describe the possible mechanisms of how PUF-8 protein systematically controls multiple cellular processes in the C. elegans germline. Since PUF proteins are evolutionarily conserved, we suggest that a similar mechanism may be involved in controlling stem cell regulation and differentiation in other organisms, including humans.
Cell Death Differ,
As a result of the genetic experiments performed in Caenorhabditis elegans, it has been tacitly assumed that the core proteins of the ''apoptotic machinery'' (CED-3, -4, -9 and EGL-1) would be solely involved in cell death regulation/execution and would not exert any functions outside of the cell death realm. However, multiple studies indicate that the mammalian orthologs of these C. elegans proteins (i.e. caspases, Apaf-1 and multidomain proteins of the Bcl-2 family) participate in cell death-unrelated processes. Similarly, loss-of-function mutations of ced-4
compromise the mitotic arrest of DNA-damaged germline cells from adult nematodes, even in a context in which the apoptotic machinery is inoperative (for instance due to mutations of egl-1
). Moreover, EGL-1 is required for the activation of autophagy in starved nematodes. Finally, the depletion of caspase-independent death effectors, such as apoptosis-inducing factor (AIF) and endonuclease G, provokes cell death-independent consequences, both in mammals and in yeast (Saccharomyces cerevisiae). These results corroborate the conjecture that any kind of protein that has previously been specifically implicated in apoptosis might have a phylogenetically conserved apoptosis-unrelated function, most likely as part of an adaptive response to cellular stress.Cell Death and Differentiation advance online publication, 29 February 2008; doi:10.1038/sj.cdd.cdd200828
In this review, we focus on the kinesin-3 family molecular motor protein UNC-104 and its regulatory protein ARL-8. UNC-104, originally identified in Caenorhabditis elegans (C. elegans), has a primary role transporting synaptic vesicle precursors (SVPs). Although in vitro single-molecule experiments have been performed to primarily investigate the kinesin motor domain, these have not addressed the in vivo reality of the existence of regulatory proteins, such as ARL-8, that control kinesin attachment to/detachment from cargo vesicles, which is essential to the overall transport efficiency of cargo vesicles. To quantitatively understand the role of the regulatory protein, we review the in vivo physical parameters of UNC-104-mediated SVP transport, including force, velocity, run length and run time, derived from wild-type and arl-8
-deletion mutant C. elegans. Our future aim is to facilitate the construction of a consensus physical model to connect SVP transport with pathologies related to deficient synapse construction caused by the deficient UNC-104 regulation. We hope that the physical parameters of SVP transport summarized in this review become a useful guide for the development of such model.