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Dr Sonia Lopez de Quinto  -  PhD


Regulation of mRNA translation in time and space

Relevance

Many biological and cellular functions rely on the generation and maintenance of cell asymmetries, also known as cell polarity. Sub-cellular mRNA localization coupled to translation in a confined cytoplasmic region has emerged as a powerful mechanism to restrict protein synthesis in time and space, leading to the polarisation of the cell. Consistent with this, local translation of asymmetrically enriched mRNAs underlies essential biological functions such as embryonic development or synaptic plasticity. Furthermore, recent work has unravelled the role of RNA-based gene regulation in the development of human diseases such as cancer, genetic neurological disorders and viral infections. Thus, understanding the mechanisms governing formation and regulation of RNA-protein complexes (RNPs) is a pre-requisite for the design of new intervention strategies.

Previous work

Using the fruit fly Drosophila as a genetically tractable model organism, and specifically the highly polarised oocyte, we have characterized different aspects of RNA regulation that control development of the future embryo's body axes. These regulatory mechanisms include the formation of transport-competent RNP particles, their interaction with the cytoskeleton, and the coordination between the transport and translation machineries.

Our recent work has revealed how the actin-based motor Myosin-V regulates the localization of oskar mRNA, the posterior determinant of the fly whose restricted expression at the posterior pole of the Drosophila oocyte is essential for the development of the future embryo. Our study has contributed to our understanding of how the actin and microtubule cytoskeletons cooperate for asymmetrical enrichment of an mRNA in a polarized cell (Krauss & Lopez de Quinto et al., 2009).

 

Immunofluorescence comparing the localization of Myosin-V (green) and a component of the oskar RNP complex (Staufen, red) during mid-oogenesis.

Immunofluorescence comparing the localization of Myosin-V (green) and a component of the oskar RNP complex (Staufen, red) during mid-oogenesis.

 

We have also identified and characterized two conserved RNA-binding proteins as key oskar regulators. Hrp48 binds to the 5´ and 3´ ends of oskar mRNA to regulate its transport to the posterior pole, while keeping the mRNA silent (Yano et al., 2004). In contrast, PTB binds preferentially to the oskar 3´UTR and, although dispensable for transport, it is essential for oskar mRNA translational repression. Our data points to PTB is a key structural component of oskar RNP complexes that functionally links formation of high-order RNP particles and translational silencing  (Besse & Lopez de Quinto et al., 2009).

 

Distribution of GFP-PTB during oogenesis. The asterisk marks the developing oocyte.

Distribution of GFP-PTB during oogenesis. The asterisk marks the developing oocyte.


 

Our research interests

Hrp48 and PTB belong to the heterogeneous nuclear ribonucleoprotein family (hnRNP) of proteins. These general RNA-binding proteins associate with transcripts as they are synthesized and control multiple aspects of RNA processing, both in the nucleus and cytoplasm. Not surprisingly, changes in the activity of these general RNA-binding proteins are associated with a broad range of developmental and cellular defects, as well as human pathologies such as cancer. However, it is still not clear how hnRNP proteins discriminate among multiple RNA targets and most importantly, the mechanisms that these RNA-binding proteins employ to specifically regulate each RNA target.

 

In wild-type egg chambers (wt), oskar mRNA (green) accumulates in the young oocyte but is translationally repressed (i.e., no Oskar protein is produced). In contrast, in ptb mutant egg chambers, Oskar protein is ectopically translated (red), indicating that PTB acts as a repressor of oskar mRNA translation.

In wild-type egg chambers (wt), oskar mRNA (green) accumulates in the young oocyte but is translationally repressed (i.e., no Oskar protein is produced). In contrast, in ptb mutant egg chambers, Oskar protein is ectopically translated (red), indicating that PTB acts as a repressor of oskar mRNA translation.


Our work aims at elucidating the principles governing the assembly and dynamics of those RNP complexes that regulate the targeting and/or translation of asymmetrically enriched mRNAs. To this end, we are using functional assays to characterize in vivo the binding of several regulatory proteins to their specific RNA targets, in a genetically tractable model organism such as the fruit fly Drosophila melanogaster. This knowledge will allow us to predict and test how newly identified RNAs may be regulated by similar proteins. By identifying new targets of regulatory RNA-binding proteins we aim at discovering new cellular processes regulated by the local expression of RNAs. This will ultimately lead to the identification of potential targets for the design of therapeutic entities, enabling us to gain control of the expression of genes in the cell cytoplasm.

The general goals of our research include:

  • Functional characterization of regulatory RNA-protein interactions.
  • Identification of conserved RNA cis-acting motifs in asymmetrically localized mRNAs regulating their localization and translation.
  • Identification of new regulatory trans-acting factors involved in the local translation of RNAs.
  • Characterization of the cellular mechanisms underlying mRNA localization and translation regulation.
  • Identification and characterization of new RNA targets associated with similar RNP complexes, using biochemical and computational approaches.
  • Elucidation of the role that local expression of asymmetrically enriched RNAs plays in different cellular and developmental processes.

We are currently recruiting new lab members. Prospective post-doctoral fellows and PhD students should have suitable qualifications and CVs to compete for studentships/fellowships. If you are interested in our work do not hesitate to contact the lab lopezdequintos@cf.ac.uk, sending your CV and a cover letter detailing your scientific interests.

Current Grant Support

RCUK Fellowship in Translational Research

Royal Society Research Grant

Collaborators

Dr. Anne Ephrussi
EMBL Heidelberg (Germany)

 Dr Encarnación Martínez-Salas
CBMSO, Madrid (Spain)

Dr. Carolina Pérez-Iratxeta
Ottawa Health Research Institute, Ottawa (Canada)

Postgraduate Research Students 

Miss Clare Pritchard