Worm Breeder's Gazette 16(4): 33 (October 1, 2000)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
The mitochondrial genome is essential for the biogenesis and function of the mitochondrial respiratory chain, the major source of ATP for most cells. It exists as 1,000 to 10,000 copies of a small circular mitochondrial DNA (mtDNA) molecule that is transcribed and translated independently of the nuclear genome. A large number of mtDNA defects (mutations, rearrangements, deletions, depletions) associated with a heterogeneous group of disorders had been described in humans.
We determined the mtDNA copy number of each of the C. elegans developmental stages as an indirect indicator of energy demands associated with development. The copy numbers per animal are: L1, 21,000 ± 6,000; L2, 22,000 ± 6,100; L3, 26,000 ± 10,000; L4, 68,000 ± 17,000; adult, 820,000 ± 190,000; glp-1(q339) L4, 69,000 ± 18,000; and glp-1(q339) adult, 81,000 ± 18,000. We conclude that a 3-fold mtDNA copy number increase from L3 to L4 is associated with somatic development, and a further 10-fold increase from L4 to adult is associated with germ-line development.
Ethidium bromide (EtBr) is a well-known inhibitor of mtDNA replication in yeast, avian, and mammalian cells and depletes mtDNA over time. We exposed staged nematodes to EtBr to access the effects of blocking the mtDNA replication. Embryonic exposure blocks the somatic mtDNA increase and results in developmental arrest as L3 larvae. Exposure of older larvae affects both the somatic and the germ-line associated copy number increases and results in some animals arresting as L4 larvae and others developing into adults with a variety of somatic and germ-line defects, including reduced overall sizes, abnormal gonad arms, reduced brood sizes, and inviable embryos.
We suggest that mtDNA copy number is tightly regulated in order to meet the energy demands associated with normal somatic and germ-line development.