Gene bru-3
D. melanogaster gene bruno-3 , abbreviated as bru-3 , encodes a putative RNA binding . Similar
sequences have been identified in Caenorhabditis elegans , Homo sapiens , Mus musculus and Rattus norvegicus . Good, P. J. et al reported a family of human RNA-binding proteins related to the Drosophila Bruno transcriptional regulator.
General function
RNA binding
Comment
Filardo P, et al 2003 reported that Bruno regulates gurken during Drosophila oogenesis.
Translational regulation of localized transcripts is a powerful mechanism to control the precise timing and localization of protein expression within a cell. In the Drosophila germline, oskar transcript must be translationally repressed until its localization at the posterior pole of the oocyte, as ectopic production of Oskar causes severe patterning defects. Translational repression of oskar mRNA is mediated by the RNA-binding protein Bruno, which binds to specific motifs in the oskar 3'UTR. Bruno over-expression causes defects in antero-posterior and dorso-ventral patterning, consistent with a role of Bruno in both oskar and gurken mRNA regulation. Bruno binds specifically to the gurken 3'UTR and that the dorso-ventral defects caused by Bruno over-expression are due to a reduction of Gurken levels in the oocyte.
Cellular localization
Cytoplasmic
Comment
Ovarian function
Oogenesis
Comment
Castagnetti S et al reported the control of oskar mRNA translation by Bruno in a novel cell-free
system from Drosophila ovaries.
The coupled regulation of oskar mRNA localization and translation in time and
space is critical for correct anteroposterior patterning of the Drosophila embryo.
Localization-dependent translation of oskar mRNA, a mechanism whereby oskar
RNA localized at the posterior of the oocyte is selectively translated and the
unlocalized RNA remains in a translationally repressed state, ensures that Oskar
activity is present exclusively at the posterior pole. Genetic experiments indicate
that translational repression involves the binding of Bruno protein to multiple
sites, the Bruno Response Elements (BRE), in the 3' untranslated region (UTR) of
oskar mRNA. The authors have established a cell-free translation system derived from
Drosophila ovaries, which faithfully reproduces critical features of mRNA
translation in vivo, namely cap structure and poly(A) tail dependence. This ovary extract, containing endogenous Bruno, is able to recapitulate oskar
mRNA regulation in a BRE-dependent way. Thus, the assembly of a
ribonucleoprotein (RNP) complex leading to the translationally repressed state
occurs in vitro. Moreover, a Drosophila embryo extract lacking
Bruno efficiently translates oskar mRNA. Addition of recombinant Bruno to this
extract establishes the repressed state in a BRE-dependent manner, providing a
direct biochemical demonstration of the critical role of Bruno in oskar mRNA
translation. The approach that we describe opens new avenues to investigate
translational regulation in Drosophila oogenesis at a biochemical level.