TITLE:
Evolutionarily conserved features of the retained intron in alternative transcripts of the nxf1 (nuclear export factor) genes in different organisms
AUTHORS:
Ludmila A. Mamon, Sergey F. Kliver, Elena V. Golubkova
KEYWORDS:
Nxf; Intron Retention; CTE; Poly(A); Drosophila; Vertebrates
JOURNAL NAME:
Open Journal of Genetics,
Vol.3 No.3,
August
28,
2013
ABSTRACT: One of the features of intron-containing genes of
the nxf (nuclear export factor) family in different organisms is the
presence of an evolutionarily conserved exon-intron block: exon 110nt-intron-exon
37nt. The intron in this evolutionarily conserved block, which we call a
“cassette” intron, can be excised or retained in alternative transcripts of nxf1.
It corresponds to intron 10 -11 inthe genes that are orthologous to nxf1 in vertebrates, and intron 5 -6 inthe genes that are orthologous to nxf1 in Drosophilidae. The
alignment of sequences of cassette introns in nxf1 genes in
vertebrates has revealed four evolutionarily conserved sequences: 1)5’flanking sequence, 2) a region
containing СТЕ (constitutive transport element), 3) third conserved sequence, and 4)3’flanking sequence. Introns 5-6 of nxf1 in Drosophilidae have no similar conserved
sequences. The results of sequence alignment demonstrate
a similarity between cassette introns of nxf1 in Drosophilidae in two poly(A) sequences. The prevalence of Dm
nxf1 transcripts containing cassette intron 5-6 under completely spliced
transcripts in the heads of adult Drosophila melanogaster suggests a
functional importance of transcripts that contain a retained intron. Evolutionary conservation, which in Drosophilidae is evident in the presence of poly(A) sequences in cassette introns of the nxf1 genes, is an adaptive feature: the poly(A) sequences are capable of mimicking
the 3’-end of
transcripts, promote transport from the nucleus to the cytoplasm, or are
involved in NMD control. The ability
to form characteristic secondary structures is a common feature of nxf1 cassette introns.