The Caenorhabditis elegans gene
mag-1 can substitute functionally for its homolog mago nashi in Drosophila and is predicted to encode a protein that exhibits 80% identity and 88% similarity to Mago nashi (P. A. Newmark et al., 1997, Development 120, 3197-3207). We have used RNA-mediated interference (RNAi) to analyze the phenotypic consequences of impairing
mag-1 function in C. elegans. We show here that
mag-1(RNAi) causes masculinization of the germ line (Mog phenotype) in RNA-injected hermaphrodites, suggesting that
mag-1 is involved in hermaphrodite germ-line sex determination. Epistasis analysis shows that ectopic sperm production caused by
mag-1(RNAi) is prevented by loss-of-function (lf) mutations in
fog-2,
gld-1,
fem-1,
fem-2,
fem-3, and
fog-1, all of which cause germ-line feminization in XX hermaphrodites, but not by a
her-1(lf) mutation which causes germ-line feminization only in XO males. These results suggest that
mag-1 interacts with the fog, fem, and gld genes and acts independently of
her-1. We propose that
mag-1 normally allows oogenesis by inhibiting function of one or more of these masculinizing genes, which act during the fourth larval stage to promote transient sperm production in the hermaphrodite germ line. When the Mog phenotype is suppressed by a
fog-2(lf) mutation,
mag-1(RNAi) also causes lethality in the progeny embryos of RNA-injected, mated hermaphrodites, suggesting an essential role for
mag-1 during embryogenesis. The defective embryos arrest during morphogenesis with an apparent elongation defect. The distribution pattern of a JAM-1::GFP reporter, which is localized to boundaries of hypodermal cells, shows that hypodermis is disorganized in these embryos. The temporal expression pattern of the
mag-1 gene prior to and during morphogenesis appears to be consistent with an essential role of
mag-1 in embryonic hypodermal organization and elongation.