Regulation of Nucleolar Size in Canorhabditis elegans (II)

Ribosome is the site for protein translation in both prokaryotes and eukaryotes. However, in contrast to the presence of nucleolus which is the factory for ribosome biogenesis in eukaryotes, there is no nucleolus in prokaryotes. How the nucleolus was evolved from prokaryotes to eukaryotes is one of the significant unanswered issues in cell biology. Several other questions regarding the nucleolus remain unsolved, such as why organisms have different sizes of nucleoli in different tissues and in tumor cells which have enlarged nucleoli or increasing number of nucleoli as compared with their normal counterparts. Hermaphrodites of Caenorhabditis elegans possess 959 somatic cells, in which intestine cells have the largest nucleolus while neuron cells have the smallest one, which provides a wonderful model to answer how the nucleolus-size is controlled. One C. elegans mutant called ncl-1 appears enlarged nucleoli in neurons and hypodermis cells. In the last few years, we established two transgenic worms, called cguIs1 (wild-type background) and cguIs1;ncl-1 and revealed a genetic network of let-7-ncl-1-fib-1 that modulates the nucleolar size in C. elegans. We also observed that disassembling of nucleolus in the -1 oocyte, the closest one to the spermatheca, is NCL-1 dependent. However, the averaged nucleolar diameter is decreased from 4.49 m in -2 oocytes to 3.93 m in -1 oocytes in ncl-1 mutants, suggesting that there is an unknown factor(s) other than NCL-1, also governing the nucleolus size. This factor remains active in early embryos, since the averaged diameter of nucleolus in embryos decreases to 2.4 m. Since the three-year proposal was only granted for a year in the past August, we will continue the theme of proposal as the previous one. Nevertheless, the priority of three specific aims is switched in this three-year application as follows, (1) to use our established transgenic worms by RNAi feeding method to define how the cep-1 gene is involved in nucleolar size control. (2) To use EMS mutagenesis method on GFP strain to search for possible genes regulating nucleolar size in oocytes and blastomeres, or other somatic cells, and (3) to create new transgenic worms expressing GFP::NCL-1, which will elusive its regulation on transcriptional and translational level, in addition, its degradation in various cell types. In addition to using genetic approaches, biochemistry and cell biology tools will also be applied. By the end of project, we hope we will reveal at least two genes (or pathways) involving in the nucleolus-size control and the obtained results can be extended to cancer cell biology studies.

Project ID:PA10308-0438
External Project ID:MOST103-2311-B182-003