Flap endonuclease 1 (Fen-1) in yeast is involved in the processing of replication intermediates and plays an important role in base excision repair. To determine biological functions of
Ce-fen-1 , a Caenorhabditis elegans flap endonuclease 1 encoded by the open reading frame Y47G6A.8, we investigated C. elegans phenotypes produced by inhibiting of the
fen-1 gene expression. RNA interference of
Ce-fen-1 resulted in embryonic lethality, egg-laying defects, and morphological abnormality of mitotic germ cells. RNA i at an elevated growth temperature of 25degC caused a protruding vulva and endomitotic oocytes as well. Ce-Fen-1 was immuno-localized to the nuclei of embryonic cells. A
Ce-fen-1::gfp fusion gene product was expressed in the nuclei of L1 stage larvae, and the expression was attenuated with the larval development. However, strong expression appeared in somatic gonad cells at the L3 and L4 stages, and in vulva cells from the L3 stage. These results suggest that
Ce-fen-1 is essential for embryogenesis and is involved in the germ-line and vulva development in C. elegans . In yeast, Dna-2 and Fen-1 interact with each other and participate in Okazaki fragment maturation. We inhibited
Ce-fen-1 gene expression in a
dna-2 (F43G6.1) deletion mutant to determine the relationship between Fen-1 and Dna-2 in C. elegans . As a result, we observed greatly enhanced defects in germ cell proliferation and oocyte development in the first generation
dna-2 homozygotes upon RNA i of
fen-1 , suggesting complementing activities of the two proteins. In order to study the interaction between
fen-1 and checkpoint genes, double RNA i was performed on
fen-1 and either one of the checkpoint genes such as
atm-1 (Y48G1BL.2),
atl-1 (T06E4.3a),
cep-1/p53 (F52B5.5) and
chk-1 (Y39H10A.7). The embryonic lethality due to
fen-1 RNA i was recovered by simultaneous RNA i of either checkpoint gene. These results suggest that replication DNA intermediates produced by
fen-1 RNA i result in embryonic lethality by inducing apoptosis through a checkpoint pathway.