Polynucleotide

Details Polynucleotide Polynucleotide

1999-07-21

2004-02-10

Ketter, James (Department: 1636)

Chemistry: molecular biology and microbiology

Animal cell, per se ; composition thereof; process of...

C435S252330, C435S320100, C536S023100, C536S024100

Reexamination Certificate

active

06689606

ABSTRACT:

The present invention relates to a polynucleotide comprising a ubiquitous chromatin opening element (UCOE) which is not derived from an LCR. The present invention also relates to a vector comprising the polynucleotide sequence, a host cell comprising the vector, use of the polynucleotide, vector or host cell in therapy and in an assay, and a method of identifying UCOEs.
The current model of chromatin structure in higher eukaryotes postulates that genes are organised in “domains” (Dillon and Grosveld, 1994). Chromatin domains can consist of groups of genes that are expressed in a strictly tissue specific manner such as the human &bgr;-globin family (Grosveld et al., 1993), genes that are expressed ubiquitously such as the human TBP/C5 locus (Trachtulec, Z. et al., 1997), or a mixture of tissue specific and ubiquitously expressed genes such as murine &ggr;/&dgr; TCR/dad-1 locus, (Hong et al., 1997; Ortiz et al., 1997) and the human &agr;-globin locus, (Vyas et al., 1992). Genes with two different tissue specificities may also be closely linked. For example, the human growth hormone and chorionic somatomammotropin genes (Jones et al., 1995). Chromatin domains are envisaged to exist in either a closed, “condensed”, transcriptionally silent state or in a “de-condensed”, open and transcriptionally competent configuration. The establishment of an open chromatin structure characterised by DNase I sensitivity, DNA hypomethylation and histone hyperacetylation, is seen as a pre-requisite to the commencement of gene expression.
The discovery of tissue-specific transcriptional regulatory elements known as locus control regions (LCRs) has provided novel insights into the mechanisms by which a transcriptionally competent, open chromatin domain is established and maintained in certain cases. LCRs are defined by their ability to confer on a gene linked in cis host cell type-restricted, integration site independent, copy number-dependent expression of the gene (Grosveld et al., 1987; Lang et al., 1988; Greaves et al., 1989; Diaz et al., 1994; Carson and Wiles, 1993; Bonifer et al., 1990; Montoliu et al., 1996; Raguz et al., 1998; EP-A-0 332 667) especially as single copy transgenes (Ellis et al., 1996; Raguz et al., 1998). LCRs are able to obstruct the spread of heterochromatin and prevent position effect variegation (Festenstein et al., 1996; Milot et al., 1996). This pattern of expression conferred by LCRs suggests that these elements possess a powerful chromatin remodelling capability and are able to establish and maintain a transcriptionally competent, open chromatin domain. In addition, LCRs have been found to possess an inherent transcriptional activating capability that allows them to confer tissue-specific gene expression independent of their cognate promoter (Blom van Assendelft et al., 1989; Collis et al., 1990; Antoniou and Grosveld, 1990; Greaves et al., 1989).
All LCRs are associated with gene domains with a prominent tissue-specific or tissue restricted component and are associated with a series of DNase I hypersensitive sites which can be located either 5′ (Grosveld et al., 1987; Carson and Wiles, 1993; Bonifer et al., 1994; Jones et al., 1995; Montoliu et al., 1996) or 3′ (Greaves et al., 1989) of genes which they regulate. In addition, LCR elements have recently been found to exist between closely spaced genes (Hong et al., 1997; Ortiz et al., 1997). An LCR-like element has also been reported to have an intronic location within a gene (Aronow et al., 1995). In the few cases that have been investigated, these elements correspond to large clusters of tissue-specific and ubiquitous transcription factor binding sites (Talbot et al., 1990; Philipsen et al., 1990; Pruzina et al., 1991; Lake et al., 1990; Jarman et al., 1991; Aronow et al., 1995).
The discovery of LCRs suggests that the regulatory elements that control tissue-specific gene expression from a given chromatin domain are organised in a hierarchical fashion. The LCR would appear to act as a master switch wherein its activation results in the establishment of an open chromatin structure that has to precede any gene expression. Transcription at the physiologically required level can then be achieved through a direct chromatin interaction between the LCR and the local promoter and enhancer elements of an individual gene via looping out of the intervening DNA (Hanscombe et al., 1991; Wijgerde et al., 1995; Dillon et al., 1997).
As indicated above, an essential feature of an LCR is its tissue specificity. The tissue specificity of an LCR has been investigated by Ortiz et al., (1997), wherein a number of DNase I hypersensitive sites of the T-cell receptor alpha (TCR&agr;) LCR were deleted and an LCR derived element, which opens chromatin in a number of tissues identified. Talbot et al., (1994, NAR, 22, 756-766) describe an LCR-like element that is considered to allow expression of a linked gene in a number of tissues. However, reproducible expression of the linked gene is not obtained. The levels of expression are indicated as having a standard deviation of between 74% from the average value on a per-gene-copy basis where the gene is expressed where transgene copy number is 3 or more. When the copy number is 1 or 2, the gene expression levels are 10 times lower and have a standard deviation of 49% from the average value on a per-gene-copy basis where the gene is expressed. The element disclosed by Talbot et al., does not give reproducible expression of a linked gene. This and the high variability of the system clearly limits the use of this system.
The long-term correction of genetically inherited disorders by gene therapy requires the maintenance and sustained expression of the transcription unit at sufficiently high levels to be of therapeutic value. This, may be achieved by one of two approaches. Firstly, transcription units can be stably integrated into the host cell genome using, for example, retroviral (Miller, 1992; Miller et al., 1993) or adeno-associated viral (AAV) vectors (Muzyczka, 1992; Kotin, 1994; Flotte and Carter, 1995). Alternatively, therapeutic genes can be incorporated within self-replicating episomal vectors comprising viral origins of replication such as those from EBV (Yates et al., 1985), human papovavirus BK (De Benedetti and Rhoads, 1991; Cooper and Miron, 1993) and BPV-1 (Piirsoo et al., 1996).
Unfortunately, the level of expression that is normally seen from genes that are integrated into the genome is too low or short in duration to be of therapeutic value in most cases. This is due to what are generally known as “position effects”. The transcription of the introduced gene is dependent upon its site of integration where it comes under the influence of either competing activating (promoters/enhancers) or more frequently, repressing (chromatin silencing) elements. Position effects continue to impose substantial constraints on the therapeutic efficacy of integrating virus-based vectors of retroviral and adeno-associated viral (AAV) origin. Viral transcriptional regulatory elements are notoriously susceptible to silencing by chromatin elements in the vicinity of integration sites. The inclusion of classical promoter and enhancer elements from highly expressed genes as part of the viral constructs has not solved this major problem (Dai et al., 1992; Lee et al., 1993).
The inclusion of a fully functional LCR as part of the transcription unit overcomes this deficiency since this element can be used to drive a predictable, physiological and sustained level of expression of the desired gene in a specific cell type (see Yeoman and Mellor, 1992, Brines and Klaus, 1993; Needham et al. 1992 and 1993; Tewari et al., 1998; Zhumabekov et al., 1995). This degree of predictability of expression is vital for a safe and successful gene therapy strategy.
The use of replicating episomal vectors (REVs) offers an attractive alternative to integrating viral vectors for producing long-term gene expression. Firstly, REVs do not pose the same size limitations on the therapeutic transcription unit as do viral vecto

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