Nucleolus, a predominant organelle present in the nucleus of eukaryotes, is the site for rRNA transcription and modification, and ribosome biogenesis. One highly phosphorylated nucleolar protein termed Nopp140 has been demonstrated to associate with rRNA transcription and nucleolus dynamics; however, its molecular mechanism remains unclear. Nopp140 was first identified in rat and its homologues have later been found extensively existing among metazoan, including human, frog, and fruit fly. Since Caenorhabditis elegans is a well-established model organism, the goal of this study was to identify the homologue of Nopp140 and to study its function in the development of worm. After genome sequence search, the ORF C25A1.10 of C. elegans was identified to be Nopp140 (designated as CeNopp140), which shares the feature of evolutionarily conserved carboxyl terminus with other Nopp140 members. C25A1.10 has been assigned a gene name,
dao-5, due to dauer larvae and age-animal would overexpress it. To know the gene expression pattern of
dao-5 during development, semi-quantitative RT-PCR was employed in various stages of worms. Results showed that the amount of RNA of CeNopp140 was the most abundant in the fourth stage larvae (L4) and adults, medium in the embryo and dauer larvae, while the least in L1-L3, indicating that various amounts of CeNopp140 are required in different developmental stages. To investigate the importance of CeNopp140 in the development of worm, a
dao-5 heterozygote strain [
dao-5(
ok542) with a ~1.7 kb deletion provided by the C. elegans gene knockout consortium] was to allow selfing. Based on sequencing result of the deletion breakpoint,
ok542 allele was inferred harboring a null mutation. By using nest PCR, no homozygous
ok542 was obtained from more than 400 arrested embryos in seven experiments, suggesting that CeNopp140 is probably required during a certain stage of development. In the future, to determine the arrested stage of C. elegans in the absence of CeNopp140 will shed light on the role of CeNopp140 in the worm development. (This work was support by the grants of CMRPD32037 and DOE89-B-FA22-2-4)