Distribution of rDNA in the nucleus of Giardia lamblia: detection by Ag-I silver stain.
OBJECTIVE
To determine whether rDNA of Giardia lamblia forms a nucleolus organizer region (NOR)-like structure and is in a very primitive state.


METHODS
G lamblia was used as the experimental animal, with Euglena gracilis as the control. The distribution was demonstrated indirectly by the modified Ag-I silver technique, which can specifically indicate the NOR under both light and electron microscopes.


RESULTS
In the ultrathin sections of silver-stained Euglena cells, all the silver grains were concentrated in the fibrosa of the nucleolus, while no grains found in the cytoplasm, nucleoplasm, condensed chromosomes or pars granulosa of the nucleus. In the silver-stained Giardia cells, no nucleolus was found; a few silver grains were scattered in the nucleus but were not concentrated in any specific region.


CONCLUSIONS
The distribution of silver grains in G lamblia showed that the transcription of rDNA occurs inside the nucleus, though no nucleolus is present. It is possible that chromosomes are in a very primitive state in diplomonad cells; as each chromosome has few prRNA genes, the transcription is independent of a nucleolus. These results imply that the rDNA of Giardia does not form a NOR-like structure and seems to represent a very primitive state in the evolution of the nucleolus.
Guo
Jian
J
College of Life Science, Nanjing Normal University, Nanjing 210097, People's Republic of China. jguo58@yahoo.com
Chen
Yonghong
Y
Zhou
Kaiya
K
Li
Jingyan
J
D000818:Animals; D002466:Cell Nucleolus / Q000648:ultrastructure; D002467:Cell Nucleus / Q000737:chemistry* / Q000648:ultrastructure; D004275:DNA, Ribosomal / Q000032:analysis*; D016829:Giardia lamblia / Q000737:chemistry / Q000235:genetics*; D016622:Silver Staining
D004275:DNA, Ribosomal