Reduction in ovulation or male sex phenotype increases long-term anoxia survival in adaf-16-independent manner inCaenorhabditis elegans

Abstract

Mendenhall AR, LeBlanc MG, Mohan DP, Padilla PA. Reduction in ovulation or male sex phenotype increases long-term anoxia survival in a daf-16-independent manner in Caenorhabditis elegans. Physiol Genomics 36: 167-178, 2009. First published December 2, 2008 doi:10.1152/physiolgenomics.90278.2008.-Identifying genotypes and phenotypes that enhance an organism's ability to survive stress is of interest. We used Caenorhabditis elegans mutants, RNA interference (RNAi), and the chemical 5-fluorodeoxyuridine (FUDR) to test the hypothesis that a reduction in progeny would increase oxygen deprivation (anoxia) survival. In the hermaphrodite gonad, germ line processes such as spermatogenesis and oogenesis can be simultaneously as well as independently disrupted by genetic mutations. We analyzed genetic mutants [glp-1(q158), glp-4(bn2ts), plc-1(rx1), ksr-1(ku68), fog-2(q71), fem-3(q20), spe-9(hc52ts), fer-15(hc15ts)] with reduced progeny production due to various reproductive defects. Furthermore, we used RNAi to inhibit the function of gene products in the RTK/Ras/MAPK signaling pathway, which is known to be involved in a variety of developmental processes including gonad function. We determined that reduced progeny production or complete sterility enhanced anoxia survival except in the case of sterile hermaphrodites [spe-9(hc52ts), fer-15(hc15ts)] undergoing oocyte maturation and ovulation as exhibited by the presence of laid unfertilized oocytes. Furthermore, the fog-2(q71) long-term anoxia survival phenotype was suppressed when oocyte maturation and ovulation were induced by mating with males that have functional or nonfunctional sperm. The mutants with a reduced progeny production survive long-term anoxia in a daf-16-and hif-1-independent manner. Finally, we determined that wild-type males were able to survive long-term anoxia in a daf-16-independent manner. Together, these results suggest that the insulin signaling pathway is not the only mechanism to survive oxygen deprivation and that altering gonad function, in particular oocyte maturation and ovulation, leads to a physiological state conducive for oxygen deprivation survival. oxygen deprivation; germ line; insulin-like signaling; stress; anoxia METAZOANS INHABITING aquatic or subterranean ecosystems have evolved mechanisms to survive changes in oxygen levels. For example, repression of energy-requiring processes or reallocation of metabolism increases oxygen deprivation survival (21). Although most terrestrial organisms live in environments where the oxygen tension does not fluctuate much, they do have the capacity to sense and respond to oxygen deprivation. In humans, oxygen deprivation is central to various health conditions including myocardial infarction, stroke, blood loss, pulmonary disorders, and solid tumor progression (37, 62). Thus identifying the molecular mechanisms that govern metazoan response to and survival of oxygen deprivation is of great interest.Oxygen deprivation tolerance spans across various phyla (7,20,53,55,68). The comparison of oxygen d...

Anoxia-Induced Suspended Animation in Caenorhabditis elegans

“…One-day old wild-type and daf-16(mu86) mutant hermaphrodites survive 72 hours of anoxia at approximately 10% and 7% respectively, and are considered long-term anoxia sensitive. In contrast, wild-type and daf-16(mu86) mutant males survive long-term anoxia with a viability >98% (Mendenhall et al, 2009). The animals maintain normal motility and demonstrate an unimpaired phenotype after long-term anoxia exposure.…”

“…If so, the additional energy expenditure while swimming in liquid media may compromise anoxia tolerance. While adult hermaphrodites are anoxia-tolerant the survival rate plummets as the duration of anoxia is lengthened (Mendenhall et al, 2006;Mendenhall et al, 2009;Padilla et al, 2002). The 1-day old adult has a markedly decreased survival rate (4.7%) in long-term anoxia, defined as a 72 hour or more anoxia exposure at 20˚C, demonstrating that there is an anoxia survival limitation (Mendenhall et al, 2006).…”

“…These steps are initiated by binding of MSP (major sperm protein) to surface receptors on the proximal oocyte (Greenstein, 2005;Miller et al, 2001). Adult hermaphrodites undergoing oocyte maturation, fertilization and ovulation do not survive long-term anoxia (Mendenhall et al, 2009). In contrast, sterile animals that do not undergo oocyte maturation and ovulation (ex: glp-1(e2141), fog-2(q71) and fem-3(q20)) and animals with reduced progeny due to a reduced rate of ovulation (ex: ksr-1(ku68)) display long-term anoxia tolerant phenotype that is daf-16 independent.…”

“…Loss of function mutations of glp-1 gene cause germ cells, located in the distal gonad that would normally undergo mitosis, to prematurely enter meiosis thus preventing formation of self-renewing germ cells and a functional germ line. Therefore, while glp-1(e2141) sterile mutants have a somatic gonad they are incapable of producing oocytes and sperm (Crittenden et al, 1994;Mendenhall et al, 2009). Anoxia survival analysis of 1-day old adult glp-1(e2141) hermaphrodites showed them to be long-term anoxia tolerant with a survival rate of approximately 98% (Mendenhall et al, 2009).…”

“…Therefore, while glp-1(e2141) sterile mutants have a somatic gonad they are incapable of producing oocytes and sperm (Crittenden et al, 1994;Mendenhall et al, 2009). Anoxia survival analysis of 1-day old adult glp-1(e2141) hermaphrodites showed them to be long-term anoxia tolerant with a survival rate of approximately 98% (Mendenhall et al, 2009). LaRue and Padilla (2011) were able to partially suppress the glp-1(e2141) long-term anoxia tolerant phenotype when the aak-2 was knocked down via RNAi in the double mutant glp-1(e2141); daf-16(mu86).…”