"The 3,UTR of
fib-1 is the target of NCL-1 suppressionJim-Ming Lee, Keng-Poo Tan, Tian Hsiang Ma and Szecheng J. LoDepartment of life Science and Graduate Institute of Microbiology, Chang Gung University, TaoYuan, TaiwanThe nucleolus of eukaryotic cells is known to be the site for ribosome assembly and the numbers and sizes of nucleoli reflect the cellular activity of ribosome synthesis. However, how organisms control the sizes and numbers of nucleoli in various types of cells is poorly understood. Caenorhabditis elegans provides a good system to answer this question. In the wild type of C. elegans, no visible nucleolus is detected in the early embryos till the 100-cell stage and the size of nucleolus is smaller in neurons and hypodermis cells than in intestine and pharynx cells. The
ncl-1 mutant exhibits nucleolus starting in the two-cell stage and a larger size of nucleolus in neurons and hypodermis cells of adult worms. Since the brat gene of Drosophila, an ortholog of
ncl-1, has been demonstrated as a translational suppressor, we searched for the target gene which is transitionally suppressed by NCL-1 in C. elegans. We identified that fibrillarin (FIB-1), one of the major nucleolar proteins with a high conservation across all eukaryotes, was a possible target of NCL-1. The results of Western blots indicated that FIB-1 was present in the embryos of
ncl-1 background worms but little or none in the wild type embryos while the results of real-time RT-PCR revealed that the level of mRNA of FIB-1 was similar in the early embryos from two different genetic background worms. We then used a GFP reporter system which contains the 3,UTR of
fib-1 fused to the end of GFP to create transgenic worms in the wild type and
ncl-1 background. GFP signals were observed in the most of cells except those in the head and tail regions of wild type worms. In contrast, GFP appeared in the entire worms in the
ncl-1 background worms. These results indicated that the 3,UTR of
fib-1 is the target of NCL-1 suppression. Whether the NCL-1 binds to the 3,-UTR of
fib-1 directly or indirectly remains to be elusive. "