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Open Access Methodology article

A simplified counter-selection recombineering protocol for creating fluorescent protein reporter constructs directly from C. elegans fosmid genomic clones

Nisha Hirani1, Marcel Westenberg14, Minaxi S Gami1, Paul Davis2, Ian A Hope3 and Colin T Dolphin1*

Author Affiliations

1 Institute of Pharmaceutical Science, King’s College London, Franklin-Wilkins Building, 150 Stamford Street, London, SE1 9NH, UK

2 EMBL-EBI, Wellcome Trust Genome Campus, Hinxton, Cambridge, CD10 1SD, UK

3 Institute of Integrative and Comparative Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK

4 Present address: Plant Protection Service (NPPO), National Reference Centre, Department of Molecular Biology, P.O. Box 9102, Wageningen, 6700HC, The Netherlands

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BMC Biotechnology 2013, 13:1  doi:10.1186/1472-6750-13-1

Published: 3 January 2013

Abstract

Background

Recombineering is a genetic engineering tool that enables facile modification of large episomal clones, e.g. BACs, fosmids. We have previously adapted this technology to generate, directly from fosmid-based genomic clones, fusion gene reporter constructs designed to investigate gene expression patterns in C. elegans. In our adaptation a rpsL-tet(A) positive/negative-selection cassette (RT-cassette) is first inserted and then, under negative selection, seamlessly replaced with the desired sequence. We report here on the generation and application of a resource comprising two sets of constructs designed to facilitate this particular recombineering approach.

Results

Two complementary sets of constructs were generated. The first contains different fluorescent protein reporter coding sequences and derivatives while the second set of constructs, based in the copy-number inducible vector pCC1Fos, provide a resource designed to simplify RT-cassette-based recombineering. These latter constructs are used in pairs the first member of which provides a template for PCR-amplification of an RT-cassette while the second provides, as an excised restriction fragment, the desired fluorescent protein reporter sequence. As the RT-cassette is flanked by approximately 200 bp from the ends of the reporter sequence the subsequent negative selection replacement step is highly efficient. Furthermore, use of a restriction fragment minimizes artefacts negating the need for final clone sequencing. Utilizing this resource we generated single-, double- and triple-tagged fosmid-based reporters to investigate expression patterns of three C. elegans genes located on a single genomic clone.

Conclusions

We describe the generation and application of a resource designed to facilitate counter-selection recombineering of fosmid-based C. elegans genomic clones. By choosing the appropriate pair of ‘insertion’ and ‘replacement’ constructs recombineered products, devoid of artefacts, are generated at high efficiency. Gene expression patterns for three genes located on the same genomic clone were investigated via a set of fosmid-based reporter constructs generated with the modified protocol.

Keywords:
C. elegans; Recombineering; Fosmid; Fluorescent protein; Deoxyribose-phosphate aldolase; Peroxiredoxin; Metallocarboxypeptidase