The DEAD-box protein MEL-46 is required in the germ line of the nematode Caenorhabditis elegans

We show that the Caenorhabditis elegans gene mel-46 (maternal effect lethal) encodes a DEAD box protein that is related to the mammalian DDX20/Gemin3/DP103 genes. mel-46 is expressed throughout development and mutations in mel-46 display defects at multiple developmental stages. Here we focus on the role of mel-46 in the hermaphrodite germ line. mel-46(yt5) mutant hermaphrodites are partially penetrant sterile and fully penetrant maternal effect lethal. The germ line of mutants shows variable defects in oogenesis. Further, mel-46(yt5) suppresses the complete feminization caused by mutations in fog-2 and fem-3, two genes that are at the top and the center, respectively, of the genetic germline sex determining cascade, but not fog-1 that is at the bottom of this cascade.The C. elegans gene mel-46 encodes a DEAD box protein that is required maternally for early embryogenesis and zygotically for postembryonic development. In the germ line, it is required for proper oogenesis. Although it interacts genetically with genes of the germline sex determination machinery its primary function appears to be in oocyte differentiation rather than sex determination.The nematode Caenorhabditis elegans has two sexes, a self-fertile hermaphrodite and a male [1]. Hermaphrodites are somatically female and undergo a transient period of spermatogenesis during the L4 larval stage. Adult worms maintain the production of oocytes throughout the rest of their reproductive life. In the distal part of the gonad, a population of mitotically dividing cells is kept proliferative by a DELTA/NOTCH type signal that originates from the distal tip cell [2] (Fig 1A). Cells that migrate proximally initiate gametogenesis. The production of mature germ cells involves a switch from mitosis to meiosis and the initiation of either male or female differentiation [3]. To initially allow spermatogenesis to take place, the oogenesis promoting gene tra-2 is translationally repressed by the action of the RNA binding