Cardiolipin (CL), also termed diphosphatidylglycerol, is a unique phospholipid that contains four fatty acyl chains. CL localizes to the mitochondrial inner membrane. During recent years CL has been attracting increasing attention as a functional phospholipid. CL plays a key role in the mitochondrial energy production, mitochondrial membrane dynamics, and regulation of mitochondrial apoptotic pathway. Although the biochemical features of CL are well investigated, its in vivo physiological functions are poorly understood. In CL de novo biosynthetic pathway, the rate-limiting and final steps are catalyzed by phosphatidylglycerophosphate (PGP) synthase and CL synthase, respectively. We identified
pgs-1 and
crls-1 genes in C. elegans genome sequences as the putative homologue of PGP synthase and CL synthase. To investigate about the physiological functions of CL, we examined the phenotypes of
pgs-1 and
crls-1 gene deletion mutants. In this meeting, we present the phenotypic data of these mutants focused on gonad developmental defects. Both mutants,
pgs-1(
tm2211) and
crls-1(
tm2542), showed sterile phenotype in hermaphrodites with impaired oogenesis and germ cell proliferation. The length and diameter of distal gonad of
pgs-1(
tm2211) were shortened to about the half of wild type, and this mutant could not generate normal oocytes.
crls-1(
tm2542) were able to generate several oocytes and lay fertilized eggs. However, the brood size of
crls-1(
tm2542) was extremely low compared to wild type, and all of these eggs failed to hatch. To further characterize this phenotype, we examined the germ cell proliferation defects of
pgs-1(
tm2211) and
crls-1(
tm2542) by the inhibition of
gld-1 pathway. In wild type,
gld-1 RNAi caused the reentry of the germ cells in the early stages of oogenesis into the mitotic cell cycle and over-proliferation. On the other hand, both mutants suppressed these germ cell phenotypes by
gld-1 RNAi. Growth and development rely on the mitochondria as the major source of ATP, and gonad has abundant mitochondria compared to other somatic tissues. One of the characteristic features of the germ cell is the continuous proliferation throughout the life. Therefore, we speculate that CL has an important role for C. elegans gonad development through the maintenance of proper germ cell proliferation.