REGULATORY ELEMENTS IN THE UPSTREAM REGION OF METALLOTHIONEIN GENE IN TILAPIA SPECIES

Abstract

Tilapia is a hardy fish which can survive in water bodies polluted with
heavy metals. Metal resistance is conferred by higher expression of
metallothionein gene (mt) in many organisms. Level, time and tissue-specificity of
gene expression is regulated through transcription factor binding sites (TFBS)
which may be present in the upstream, downstream, or even in the introns of a
gene. So, as a candidate regulatory region, the 5’upstream sequence of mt gene in
three tilapia species, Oreochromis aureus, O. niloticus and O. mossambicus was
studied. The targeted region was PCR-amplified and then sequenced using a pair
of custom-designed primer. A total of only 2.7% variation was found in the
sequenced genomic region among the three species. Metal-related TFBS were
predicted from these sequences. A total of twenty eight TFBS were found in O.
aureus and twenty nine in O. mossambicus and O. niloticus. The number of metalrelated
TFBS predicted in the targeted sequence was significantly higher
compared to that found in randomly selected other genomic regions of same size
from O. niloticus genome. Thus, the results suggest the presence of putative
regulatory elements in the targeted upstream region which might have
important role in the regulation of mt gene function.