Mitochondrial Respiratory Chain Deficiency inCaenorhabditis elegans Results in Developmental Arrest and Increased Life Span

Abstract

The growth and development of Caenorhabditis elegans are energy-dependent and rely on the mitochondrial respiratory chain (MRC) as the major source of ATP. The MRC is composed of ϳ70 nuclear and 12 mitochondrial gene products. Complexes I and V are multisubunit proteins of the MRC. The nuo-1 gene encodes the NADH-and FMN-binding subunit of complex I, the NADH-ubiquinone oxidoreductase. The atp-2 gene encodes the active-site subunit of complex V, the ATP synthase. The nuo-1(ua1) and atp-2(ua2) mutations are both lethal. They result in developmental arrest at the third larval stage (L3), arrest of gonad development at the second larval stage (L2), and impaired mobility, pharyngeal pumping, and defecation. Surprisingly, the nuo-1 and atp-2 mutations significantly lengthen the life spans of the arrested animals. When MRC biogenesis is blocked by chloramphenicol or doxycycline (inhibitors of mitochondrial translation), a quantitative and homogeneous developmental arrest as L3 larvae also results. The common phenotype induced by the mutations and drugs suggests that the L3-to-L4 transition may involve an energy-sensing developmental checkpoint. Since ϳ200 gene products are needed for MRC assembly and mtDNA replication, transcription, and translation, we predict that L3 arrest will be characteristic of mutations in these genes. The human mitochondrial respiratory chain (MRC)1 is composed of Ͼ80 subunits, but requires Ͼ100 additional genes for its assembly (1). These additional genes encode the import apparatus for transporting polypeptides into the organelle, chaperones, and other assembly factors, as well as the machinery needed to replicate, transcribe, and translate the 13 MRC subunits encoded by mtDNA. The MRC generates the majority of cellular ATP. Thus, the loss of one member of this large class of genes can compromise the entire pathway of energy production. The consequences of such events are diverse and debilitating (2-4). The metabolism and structure of the Caenorhabditis elegans MRC closely parallel its mammalian counterpart (5). Moreover, the nematode mtDNA is similar in size and gene content to the human mtDNA (6).The MRC is organized into five multisubunit proteins. Complexes I-IV form the electron transport chain, which couples the oxidation of NADH and succinate to the reduction of oxygen and the formation of a proton gradient. Complex I (NADHubiquinone oxidoreductase) is an elaborate enzyme that catalyzes the transfer of electrons from NADH to ubiquinone. Bovine complex I consists of ϳ43 subunits, an FMN cofactor, and up to eight iron-sulfur clusters (7, 8). The FMN-and NADHbinding sites, as well as one iron-sulfur cluster, are considered to reside in the 51-kDa subunit. One predicted C. elegans gene product (C09H10.3) bears strong sequence resemblance (75% identical amino acids) to the human gene. We have designated the gene encoding the C. elegans NADH-ubiquinone oxidoreductase 51-kDa subunit as nuo-1. Complex I deficiency is one of the most frequently encountered mitochondrial defects (9 -11). Mutat...

The Mitochondrial Prohibitin Complex Is Essential for Embryonic Viability and Germline Function in Caenorhabditis elegans

“…Mitochondria and a functional MRC are essential to fulfill the energy requirements during nematode growth and development (35). An energy-related developmental checkpoint at the L3 to L4 transition has been proposed in situations of seriously impaired MRC function (41).…”

“…The C. elegans RNAi phenotypes for prohibitins resemble those of known MRC genes (35) (see also RNAi phenotypes for mev-1 and isp-1 on the World Wide Web at www.wormbase.org/). Therefore, it will be interesting to determine whether phb null mutants can be maternally rescued and develop to the L3 stage as seen with the null MRC mutants (35) and to determine how hypomorphic phb mutations will affect nematode growth and development. Fully understanding the scope and severity of effects on mitochondrial function arising from the lack of prohibitins will help to further elucidate the molecular mechanism of action of the PHB complex and its precise role in mitochondrial biogenesis.…”

“…Doxycycline slows worm development and, at concentrations equal to or above 60 g/ml, causes developmental arrest at the L3 stage (35). In four independent experiments, the increase in PHB protein levels varied between 30 and 40% after 72 h of treatment when compared with controls (Fig.…”

ATP-2 Interacts with the PLAT Domain of LOV-1 and Is Involved inCaenorhabditis elegansPolycystin Signaling

“…atp-2 is an essential gene (Gonczy et al, 2000;Tsang et al, 2001). atp-2(ua2) mutants arrest at the third larval stage (L3), and both atp-2(ua2) and atp-2 RNAi result RNAi knock-down components from MRC complex V but not Complex I, II, or III affects the response, but not vulva location, step of mating behavior.…”

“…The mitochondrial ATP synthase (also referred to as the mitochondrial respiratory chain [MRC] complex V) is a multimeric enzyme consisting of the soluble F 1 and membrane-bound F 0 complexes. C. elegans ATP-2 is the ␤ subunit, or active site, of the F1 portion (Tsang et al, 2001). The MRC generates the majority of cellular ATP.…”