Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-10-03
2002-07-16
Fredman, Jeffrey (Department: 1655)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S023100, C536S024300, C536S024310, C536S024320, C536S024330, C135S022000
Reexamination Certificate
active
06420548
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The invention relates to a method of regulating the transcription of transgene in genetically-modified organisms. More specifically, the invention relates to the use of expression vectors harboring the coding sequence of a gene of interest under the transcriptional control of promoting sequences for which activity is regulated by the presence of nitrogen. Preferably, these constructs are used in transgenic leguminous plants (for example soybean, alfalfa, clover, birdsfoot trefoil, beans, peas, peanuts) where growth is not impaired by lack of mineral nitrogen, and in which induction of expression could be performed at any given time during development, through the addition of a suitable nitrogen source. In a broader perspective, the invention could be used to induce expression of any given transgene through the addition of any nitrogen source, provided that the organism can be grown adequately in the absence of this nitrogen inducer; as an example within the plant kingdom, duckweed (Lemna minor) can adapt to grow either on nitrate or ammonium as nitrogen source; transgenic duckweed could therefore be grown on nitrate as a sole nitrogen source and expression of the transgene triggered by the addition of ammonium, provided that the cassette contains a promoter from a native gene for which expression is turned on by the addition of ammonium. The invention therefore provides a means of regulating the expression of a transgenic trait in any organism through the addition of various nitrogenous inducer.
(b) Description of Prior Art
Nitrogen is a molecule essential to life. All living organism need nitrogen in order to synthesize amino acids, the building blocks of proteins, and nucleotides, the building blocks of nucleic acids. It is Ammonium nitrate is the preferred form of mineral nitrogen provided to crops in the form of fertilizer. Nitrate-nitrogen is first reduced to nitrite and then to ammonium through the activity of a metabolic pathway common to most herbaceous plants. Depending on the species, part or all of the absorbed nitrate will move to leaf cells through the xylem before it is reduced to ammonium. Ammonium, or other reduced forms of nitrogen are also absorbed (although usually at lower rates) by the root system but their assimilation does not require reduction. These newly absorbed ammonium or ammonium-containing molecules join the endogenous pools in the cells which is formed by ammonium cycling through amino acids and other nitrogenous molecules. Some species do not metabolize nitrate-nitrogen easily and therefore cannot rely on nitrate as sole nitrogen source; many coniferous species fall into this latter category. Legumes and other symbiotic plant species form a third large class of nitrogen user within the plant kingdom; they form a metabolic alliance with a microbial organism through which they can fix gaseous nitrogen. This reduced nitrogen is used efficiently by the plant for growth, and therefore, these crops can develop independently of the availability of mineral nitrogen in the soil.
Many microbes and wild plant species will adapt extensively to availability of nitrogen sources and can therefore complete their life cycle in the absence of one molecular form of nitrogen, which they could use exclusively and efficiently if available in another growing environment. As for most assimilatory pathways, nitrogen assimilation is tightly regulated in cells. As an example, the expression of genes encoding nitrate reductase (NaR) and nitrite reductase (NiR), which are responsible for the reduction of nitrate to ammonium, has been extensively described in various microbial and plant species (for a review, see Miflin and Lea, Books 5 and 12 in
The Biochemistry of plants
). Although nitrate is not the only regulatory molecule involved in the control of NaR and NiR expression, its presence is essential to initiate the cascade of transduction that eventually leads to sustained transcription and translation of these genes. It has been shown that expression of NaR and NiR genes is repressed in leguminous plants when they are grown in the absence of mineral nitrogen
NiR promoters have been characterized in some plant species (Back et al., 1991,
Plant Molecular Biology
17:9-18; Sander et al., 1995,
Plant Molecular Biology
27:165-177). Inducibility of these promoters have also been characterized using marker genes in transgenic plants, where it was shown that availability of nitrate is required for full activation of transcription.
Assimilatory pathways for other nitrogen sources have also been described, and promoters for genes involved in some of these pathways have also been characterized.
Genetic transformation of microbes have been used for more than 15 years to produce useful recombinant molecules, and applications in the pharmaceutical, cosmaceutical and dermaceutical industries are being currently exploited. This technology has expanded from microbes to plants and animals in the last ten years with the development of techniques required to adapt this general concept to complex eukaryotic organisms. Basically a gene encoding for a protein of interest or a gene encoding for an enzyme responsible for a modification of a metabolic pathway that leads to a molecule of interest, is linked in an appropriate fashion to cis-and trans-acting regulatory sequences, and transferred to a target cell where it is incorporated in the molecular machinery (in a transitory or stable fashion). The transgenic cell, or a tissue or organism regenerated from the transgenic cell will then perform transcription and translation of the transgene and therefore be enabled to accumulate the protein of interest or to perform the new metabolic reaction through the activity of the enzyme of interest.
The emerging industry of molecular farming (production of recombinant molecules in animals or crops) is one of the most promising industry of the coming century. Its promise is to provide safe and renewable molecule factories for the industry. Among the applications that are currently developed are the production of low-cost monoclonal antibodies for therapeutic and diagnostic uses, the production of unlimited amounts of hormones, cytokines and other bio-active molecules for the treatment of chronicle or lethal diseases, the production of bio-safe substitutes for various blood components, the production of unlimited amounts of processing enzymes for the food and pulp industry, the production of low-cost enzymes for waste treatments, and the production of safe bio-active molecules for the cosmetic industry.
Limitations to the application of this technology has often come from the inability of transgenic organisms to accumulate adequate amounts of the recombinant product, as a result of low transcription rates, improper splicing of the messenger, instability of the foreign mRNA, poor translation rates, hyper-susceptibility of the recombinant protein to the action of endogenous proteases or hyper-susceptibility of the recombinant organism to the foreign protein which result in improper and limited growth or in the worst cases, in strong deleterious effects to the host organism. Inadequacy of production level has a direct impact on the development of applications when profit margins are narrow, or when treatment and/or disposal of residual matter causes bio-safety or environmental problems. Improvement of the accumulation level of the desired recombinant product thus appears to be one critical factor that warrants commercialization of many applications of molecular farming.
The use of inducible promoters has been proposed, and in some instances used successfully, to counteract the combined effect of all the above-mentioned factors. Strong inducible promoters may succeed in generating high ephemerous transcription rates which result in high transitory accumulation of foreign mRNA and translational product. As a result, when inducibility of expression is paired with adequate synchronized protein recovery procedures, the yield per unit obtained is higher th
D'Aoust Marc-André
Vezina Louis-Philippe
Cawthorn Christian
Côté France
Fredman Jeffrey
Medicago Inc.
Swabey Ogilvy Renault
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