Building 45 (Natcher) 6th Floor South Conference Room
Monday November 4, 11 AM

Igor B. Rogozin

Remarkable conservation of intron positions in plants and vertebrates and
massive, lineage-specific loss of introns in eukaryotic evolution
Eukaryotic protein-coding genes typically contain introns that are spliced
out of the pre-mRNA by a distinct, large RNA-protein complex, the
spliceosome. Anecdotal observations indicate that positions of some introns
are conserved in orthologous genes from plants and animals. However, intron
densities in different eukaryotic species differ widely and the location of
introns in orthologous genes does not always coincide even in closely
related species. Thus, both intron loss and intron insertion clearly occur
in eukaryotic evolution. It has been suggested that the proportion of
shared intron positions decreased with increasing evolutionary distance,
which potentially could make intron conservation a useful phylogenetic
marker. In general, however, tempo and mode of intron evolution remain
poorly understood and it is unclear whether the genome of the common
ancestor of animals, plants and fungi was intron-rich or intron-poor, how
many ancestral introns are retained in extant genomes and what are the
relative contributions of intron loss and intron insertion in the evolution
of eukaryotic genes. We analyzed the intron positions in 98 orthologous
gene sets from six completely sequenced genomes of animals, plants and
fungi and constructed parsimonious scenarios of evolution of the
exon-intron structure for the respective genes. Paradoxically, humans share
more introns with Arabidopsis than with fly or nematode. This is explained
by postulating the presence of a substantial number of introns in the
common ancestor of animals, plants and fungi. Many of these ancestral
introns appear to have been conserved in vertebrates and plants but lost in
fungi, nematodes and arthropods.


Igor B.Rogozin
National Center for Biotechnology Information
National Library of Medicine
National Institutes of Health, Bldg. 38A
Bethesda, MD 20894, USA
Voice: (301)594-4271
Fax: (301)480-9241
email rogozin@ncbi.nlm.nih.gov