Abstract
BackgroundThe multicellular green alga Volvox carteri represents an attractive model system to study various aspects of multicellularity like cellular differentiation, morphogenesis, epithelial folding and ECM biogenesis. However, functional and molecular analyses of such processes require a wide array of molecular tools for genetic engineering. So far there are only a limited number of molecular tools available in Volvox.ResultsHere, we show that the promoter of the V. carteri nitrate reductase gene (nitA) is a powerful molecular switch for induction of transgene expression. Strong expression is triggered by simply changing the nitrogen source from ammonium to nitrate. We also show that the luciferase (g-luc) gene from the marine copepod Gaussia princeps, which previously was engineered to match the codon usage of the unicellular alga Chlamydomonas reinhardtii, is a suitable reporter gene in V. carteri. Emitted light of the chemiluminescent reaction can be easily detected and quantified with a luminometer. Long-term stability of inducible expression of the chimeric nitA/g-luc transgenes after stable nuclear transformation was demonstrated by transcription analysis and bioluminescence assays.ConclusionTwo novel molecular tools for genetic engineering of Volvox are now available: the nitrate-inducible nitA promoter of V. carteri and the codon-adapted luciferase reporter gene of G. princeps. These novel tools will be useful for future molecular research in V. carteri.
Highlights
The multicellular green alga Volvox carteri represents an attractive model system to study various aspects of multicellularity like cellular differentiation, morphogenesis, epithelial folding and ECM biogenesis
We demonstrate that the promoter of the V. carteri nitrate reductase gene is a powerful molecular switch for induction of transgene expression
Chimeric selectable marker and reporter genes for transformation For all transformation experiments, the Streptomyces rimosus aphVIII gene that confers resistance to paromomycin was used as a selectable marker [8]
Summary
The multicellular green alga Volvox carteri represents an attractive model system to study various aspects of multicellularity like cellular differentiation, morphogenesis, epithelial folding and ECM biogenesis. Various aspects of multicellularity like cellular differentiation, morphogenesis, epithelial folding and ECM biogenesis have been studied in Volvox and its close relatives in the group of the volvocine algae [1,2]. Comparisons among volvocine algae open the the technical feasibility of genetically manipulating a species of interest is a key factor for any detailed molecular analysis of gene or protein functions in order to reveal key aspects in development and evolution. Even if several promoters are available for genetic manipulations in V. carteri, there is a need for a strong, inducible promoter that can be switched on without affecting further development of the organism. Further inducible Volvox promoters have not been investigated so far
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