The nucleolus is the most prominent structure in the interphase nucleus of a
eukaryotic cell, and ribosomal biogenesis is its main function. However, the nucleolus
does not emerge in prokaryotic cells at all, though ribosome biogenesis also occurs in
them. Actually, up to date, how the nucleolus arose during the process of the evolution
of eukaryotic cells from prokaryotic cells remains an open question. And the
evolutionary assembly of nucleolar network from prokaryote to eukaryote is also an
interesting issue. At present, the rapid accumulation of genomic and proteomic data
has already provided us an opportunity to resolve these issues on the
genomic/proteomic level.
1) At present, three nucleolar protein genomes are available, Homo sapiens,
Arabidopsis thaliana, and Saccharomyces cerevisiae. We compared the three
nucleolar protein genomes to find the shared orthologous groups, which called
eukaryotic basic nucleolar proteome I (EBNP I). As the limited number of A.
thaliana and S. cerevisiae nucleolar protein genomes, the human nucleolar protein
genome were then compared with the whole genomes of these two species, and
the shared orthologous groups by the three were called EBNP II. The homology
relationships between the human nucleolar proteins in both EBNP I and EBNP II
and prokaryotic genomes testify chimeric nature of the nucleolus. Functional
inventory of the human nucleolar proteins in EBNP reveals the origin of each
functional class occurs within the nucleolus.
2) The budding yeast protein interaction data is more complete than others, and the
nucleolar protein genome is also available, which provide us an opportunity to
investigate the evolutionary assembly of nucleolar network from prokaryote to
eukaryote. Here we showed a gradually complicated process in the evolutionary
history of budding yeast nucleolus. In the evolutionary steps from prokaryote to
eukaryote, nucleolus recruited proteins step by step and the recruited proteins
were asymmetrically involved into the network. Furthermore proteins which
originated from prokaryotes exert core function in the assembly of the nucleolus
network. The whole network of nucleolus in yeast was constructed based on the
framework of prokaryotic homologs. The recruitments subsequently were
integrated into the framework and made the former proteins more complicated.
Our results not only indicated that prokaryotic homologs are the centre of
nucleolus network and also would shed light on the physiological assembly of
nucleolus in cell.
修改评论