RNA Localisation in Drosophila

Repeated pattern in Drosophila is established by the pair-rule segmentation genes. These are expressed in anteroposterior stripes in the syncytial blastoderm embryo, and encode transcription factors, which act in combination to specify reiterated domains of target gene expression.

(a) Hairy protein is expressed in seven stripes in the blastoderm embryo. (b) Peripheral stripes of pair-rule transcripts hairy (green) and fushi tarazu(red) adjacent to the cortical nuclei (blue). (c) Higher magnification of embryo showing apical localisation of hairy and fushi tarazu transcripts. Anterior is to the left; dorsal is upwards.

Pair-rule segmentation transcripts accumulate exclusively apically of the peripheral layer of somatic nuclei, under the influence of signals that usually lie within their 3'-UTRs (Davis and Ish-Horowicz, 1991). To study the mechanism and function of localisation, we have established rapid assays using fluorescent transcripts in which injected pair-rule transcripts localise specifically apically in blastoderm embryos via microtubule-based motors (Lall et al.,1999).

Transport of injected hairy transcripts in the blastoderm embryo

Using these assays we find that:

• The Egalitarian and Bicaudal-D proteins, previously implicated in oocyte determination and differentiation, act directly in RNA transport, comprising part of the dynein motor that drives localisation (Bullock and Ish-Horowicz, 2001).
• The same motor machinery drives RNA transport in early oocytes, and in blastoderm embryos and developing neuroblasts (Bullock and Ish-Horowicz 2001, Hughes et al , 2004)
• Timelapse microscopy of injected localising transcripts reveals the kinetics of transport, and indicates that the efficiency of the dynein motor is modulated by the nature of its cargo (Bullock et al, 2003).
• Transcript localisation, although not essential for protein localisation during segmentation and in polar neuroblasts, is required to achieve peak localised protein activities (Bullock et al 2004, Hughes et al 2004).

Current research interests:

1. Analysing the structural features in RNA signals that are recognised by the localisation machinery.
2. Using biochemistry and genetics to identify further components of the RNA transport complex with a view to understanding the protein basis of its specificity
3. Investigating how DNA damage may regulate molecular motors, in particular, how motor activity is affected such that blastoderm nuclei become internalised in response to DNA damage

Techniques

Microinjection of DNA and Fluorescent RNA; Double stranded RNA interference; Drosophila genetics; In situ hybridisation; Cell culture.

Lab members: Chris Molenaar, Inbal Ringel, Mark Wainwright, Krzysztof Wicher, Emmanuel Vanrobays