VRK-1, a vaccinia-related kinase in C. elegans, has multiple functions throughout development. It is required for nuclear envelope formation during embryogenesis and for germ line proliferation and vulval morphogenesis during larval development. The Drosophila ortholog, NHK-1, is a histone kinase, mutant alleles of which affect chromosome morphology in oocytes. We have an ongoing interest in proteins that influence chromosome morphology and behavior during the meiotic divisions in C. elegans. We have begun to examine the phenotypes of embryos depleted of the vrk-1 gene, using RNAi. We have observed highly penetrant embryonic lethality. These embryos display defects in the meiotic divisions as well as a failure to decondense chromatin. As a result, these embryos arrest as multicellular embryos with very little DNA. This defect is not a result of nuclear envelope defects in the developing oocytes nor in any other aspect of germ line development. We believe the VRK-1 protein is affecting the histone modifications of the meiotic chromosomes of the oocyte and thus is perturbing their ability to properly organize for the meiotic divisions that follow fertilization. We are using real time imaging of live embryos expressing GFP-tagged histones to follow the developmental defects that occur upon vrk-1 depletion. We are also using immunocytochemistry to determine whether any specific histone modifications are perturbed at this time to account for the observed meiotic defects. ? We are also in the process of screening for mutant alleles of vrk-1, which would allow us to study its many functions throughout development. A deletion allele does exist and results in sterility. We are using TILLING to screen for point mutations in the vrk-1 gene. With useful alleles of vrk-1, we may be able to further dissect the vrk-1 pathway in C. elegans using a genetic suppressor screen.