[
2017]
An organism's health depends on the integrity of molecular and biochemical networks responsible for ensuring homeostasis within its cells and tissues. However, upon aging, a progressive failure in the maintenance of this homeostatic balance occurs in response to various insults, allowing the accumulation of damage, the physiological decline of individual tissues, and susceptibility to diseases. Despite the complex nature of the aging process, simple genetic and environmental alterations can cause an increase in healthy lifespan or "healthspan" in laboratory model organisms. Genetic manipulations of model organisms including yeast, worms, flies, and mice have revealed signaling elements involved in DNA damage, stem cells maintenance, proteostasis, energy, and oxidative metabolism (Riera et al., 2016). However, one of the most intriguing discoveries made in these models resides in the ability of environmental factors to profoundly alter the aging process by remodeling some of the genetic programs mentioned above (Riera and Dillin, 2016). The first line of evidence that an external cue could powerfully regulate longevity was obtained by performing dietary restriction in rodents, a reduction in food intake without malnutrition. Dietary restriction is the most robust intervention to increase lifespan in model organisms including rodents and primates, and delays the emergence of age-related diseases (Mair and Dillin, 2008). How dietary restriction extends lifespan remains an open question, but decades of research are evidencing molecular pathways embedded in the response to reduce energy availability, resulting in the emergence of an altered metabolic state that promotes health and longevity. Nonetheless, the discovery of dietary restriction opened a new avenue of research in the aging field, and in particular in the understanding of how animals deal with fluctuating energy levels in their natural environment, and how their longevity is affected by such factors. This is particularly relevant for the nematode Caenorhabditis elegans, which survives in a changing environment and must be able to coordinate energy-demanding processes including basal cellular functions, growth, reproduction, and physical activity with available external resources. In order to sense their environment, C. elegans possess ciliated sensory neurons located primarily in sensory organs in the head and tail regions. Cilia function as sensory receptors, expressing many G protein-coupled receptors (GPCRs) and transient receptor potential (TRP) channels, and mutants with defective sensory cilia have impaired sensory perception (Bargmann, 2006). Cilia are membrane-bound microtubule-based structures and in C. elegans are only found at the dendritic endings of sensory neurons. Sensory neurons provide nematodes with a remarkable form of developmental plasticity, allowing them to assess food availability, temperature, and crowding information (worm density) in order to arrest their development if required, thus forming long-lived and stress-resistant dauer larvae (Bargmann, 2006; Golden and Riddle, 1982). When favorable times return, worms assess the same cues to recover and resume normal development. As the entry and exit of the dauer larval stage suggest, worm sensory neurons truly function as neuroendocrine organs, being implicated in many physiological functions in addition to their behavioral role (Bargmann, 2006). Much information on these neurons has been gathered from laser ablation experiments and analysis of mutants presenting defects in sensory cilia. A seminal discovery in the aging field was achieved when the laboratory of Cynthia Kenyon showed in 1999 that mutations that cause various defects in cilia formation, including the absence of cilia, deletion of middle and distal segments, or impair chemosensory signal transduction increase longevity profoundly (Apfeld and Kenyon, 1999). Later, this group also demonstrated that laser ablation of specific pairs of gustatory and olfactory chemosensory neurons was sufficient to extend lifespan (Alcedo and Kenyon, 2004). What is the role of TRP channels in modulating these neuroendocrine processes, and what kind of stimuli are these receptors detecting to control aging? This chapter summarizes relevant discoveries that clarify some of the roles of TRP channels in the aging process.
[
1986]
Wild-type body wall muscle cells of Caenorhabditis elegans produce at a constant ratio two myosin heavy chain isoforms, A and B, that form homodimeric myosins. Electron microscopy of negatively stained complexes of isoform-specific antibodies with isolated thick filaments shows that the surface of the 9.7 =B5m long filament is differentiated with respect to myosin content: a medial 1.8 =B5m zone contains myosin A and two polar 4.4 = =B5m zones contain myosin B. Biochemical and electron microscopic studies show that at 0.45 M KC1, pH 6.35, myosin B and paramyosin are solubilized. The medial all-myosin A region with novel core structures extending in a polar manner remain. These dissociation experiments suggest a sequential model for wild-type thick filament assembly in which myosins A and B would participate in the initiation and termination of assembly, respectively. Analysis of mutant thick filaments clarifies the relationship of the myosin isoforms. CB190 (
unc-54 I) thick filaments contain myosin A only and have normal length. CB1214 (
unc-15 I) mutants produce no paramyosin, and their thick filaments are composed of a medial myosin region
[
Cell Calcium,
2011]
IP receptor is a Ca(2+) release channel localized on the endoplasmic reticulum. IP(3) receptor is composed of three isoforms, which are expressed in various cells and tissues, and play variety of roles throughout development. I here describe the role of IP receptor from oogenesis, meiotic maturation and fertilization. I also describe the Ca(2+) signaling at meiosis and mitosis, and especially the role in early embryogenesis to determine dorso-ventral axis formation. Loss of function mutation of type 1 IP receptor in mouse, both by gene targeting and spontaneous mutations shows severe ataxia and other phenotypes. Interestingly, double knockouts of type 1 and type 2 exhibit cardiogenesis arrest and that of type 2 and type 3 results in exocrine secretion deficit. IPR of Drosophila or Caenorhabditis elegans is single gene and mutation results severe phenotype of behavior. All the data described here show that IPRs are essential for life and abnormality of IP(3)Rs results in severe abnormality in its structure and function of organism.
[
Handb Exp Pharmacol,
2007]
In signal transduction of metazoan cells, transient receptor potential (TRP) ion channels have been identified that respond to diverse external and internal stimuli, among them osmotic and mechanical stimuli. This chapter will summarize findings on the TRPV subfamily, both its vertebrate and invertebrate members. Of the six mammalian TRPV channels, TRPV1, -V2, and -V4 were demonstrated to function in transduction of osmotic and/or mechanical stimuli. TRPV channels have been found to function in cellular as well as systemic osmotic homeostasis in vertebrates. Invertebrate TRPV channels, five in Caenorhabditis elegans and two in Drosophila, have been shown to play a role in mechanosensation, such as hearing and proprioception in Drosophila and nose touch in C. elegans, and in the response to osmotic stimuli in C. elegans. In a striking example of evolutionary conservation of function, mammalian TRPV4 has been found to rescue mechanosensory and osmosensory deficits of the TRPV mutant line
osm-9 in C. elegans, despite no more than 26% orthology of the respective amino acid sequences.
[
Annu Rev Biochem,
2004]
Researchers have long predicted that complex carbohydrates on cell surfaces would play important roles in developmental processes because of the observation that specific carbohydrate structures appear in specific spatial and temporal patterns throughout development. The astounding number and complexity of carbohydrate structures on cell surfaces added support to the concept that glycoconjugates would function in cellular communication during development. Although the structural complexity inherent in glycoconjugates has slowed advances in our understanding of their functions, the complete sequencing of the genomes of organisms classically used in developmental studies (e.g., mice, Drosophila melanogaster, and Caenorhabditis elegans) has led to demonstration of essential functions for a number of glycoconjugates in developmental processes. Here we present a review of recent studies analyzing function of a variety of glycoconjugates (O-fucose, O-mannose, N-glycans, mucin-type O-glycans, proteoglycans, glycosphingolipids), focusing on lessons learned from human disease and genetic studies in mice, D. melanogaster, and C. elegans.
[
FEBS Lett,
2010]
Autophagy is an evolutionarily conserved intracellular catabolic system. During Caenorhabditis elegans development, autophagy plays an important role in many physiological processes, including survival under starvation conditions, modulation of life span, and regulation of necrotic cell death caused by toxic ion-channel variants. Recently, it has been demonstrated that during embryogenesis, basal levels of autophagy selectively remove a group of proteins in somatic cells, including the aggregate-prone components of germline P granules. Degradation of these protein aggregates provides a genetic model to identify essential autophagy components and also to elucidate how the autophagic machinery selectively recognizes and degrades specific targets during animal development.
[
Science,
2003]
Small RNAs, including microRNAs (miRNAs) and short interfering RNAs (siRNAs), are key components of an evolutionarily conserved system of RNA-based gene regulation in eukaryotes. They are involved in many molecular interactions, including defense against viruses and regulation of gene expression during development. miRNAs interfere with expression of messenger RNAs encoding factors that control developmental timing, stem cell maintenance, and other developmental and physiological processes in plants and animals. miRNAs are negative regulators that function as specificity determinants, or guides, within complexes that inhibit protein synthesis (animals) or promote degradation (plants) of mRNA targets.