Cardiolipin (CL) is a major membrane phospholipid that localizes to the mitochondrial inner membrane. Recently, CL has been paid attention as a functional phospholipid. At the cellular level, CL has been shown to have a role in the mitochondrial energy production, mitochondrial membrane dynamics, and apoptosis triggering. Although the biochemical features or cellular function of CL are well investigated, its in vivo physiological functions are poorly understood. In this study, by generating deletion mutants of CL synthase gene (
crls-1), we show that CL is required for the gonad development in C. elegans.
To ensure that the CRLS-1 protein actually has a CL synthase activity, we determined the CL content in worms whose
crls-1 gene was knocked down by RNAi. In
crls-1(RNAi) worms, the CL content was decreased to 39% that of mock RNAi worms. Concurrently, PG content, which is the precursor of CL, was increased to about eight-fold that of mock RNAi. Knock down of
crls-1 did not substantially affect on other phospholipid contents. These data indicate CRLS-1 is a functional homolog of CL synthase in C. elegans.
crls-1 mutants,
crls-1(
tm2542), showed sterile phenotype in hermaphrodites with impaired oogenesis and reduced germ cell number.
crls-1 mutants produced 6-8 eggs per worm, and all of these eggs failed to hatch. The reduced brood size of
crls-1 mutants were restored by introduction of
crls-1 gene under the control of heat shock promoter, indicating the deletion of
crls-1 gene is responsible for the sterility of
crls-1 mutants. To further examine the reduction of germ cell number in
crls-1 mutants, we generated a double mutants
crls-1(
tm2542)
glp-1(
ar202).
glp-1(
ar202) is a gain-of-function mutant allele, in which the GLP-1/Notch signaling pathway in gonad is constitutively activated, and the germ cells divide mitotically throughout the gonad arm. In
crls-1(
tm2542)
glp-1(
ar202), the size of gonad and the number of germ cells were remained to be reduced as compared with
glp-1(
ar202) single mutants, indicating that the reduction of germ cell number in
crls-1 mutants is not caused by down-regulation of the GLP-1/Notch signaling.
Therefore, CL could have an important role for C. elegans gonad development through the maintenance of proper germ cell proliferation.