Comparative fluorescence hybridization to nucleic acid arrays

Details Comparative fluorescence hybridization to nucleic acid arrays Comparative fluorescence hybridization to nucleic acid arrays

1996-06-26

2003-05-13

Myers, Carla J. (Department: 1654)

Chemistry: molecular biology and microbiology

Measuring or testing process involving enzymes or...

Involving nucleic acid

C435S005000, C435S091100, C435S091200, C536S024300

Reexamination Certificate

active

06562565

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to methods for detecting and mapping genetic abnormalities associated with various diseases. In particular, it relates to the use of nucleic acid hybridization methods for comparing copy numbers of particular nucleic acid sequences in a collection of sequences relative to the copy number of these sequences in other collections of sequences.
Many genomic and genetic studies are directed to the identification of differences in gene dosage or expression among cell populations for the study and detection of disease. For example, many malignancies involve the gain or loss of DNA sequences resulting in activation of oncogenes or inactivation of tumor suppressor genes. Identification of the genetic events leading to neoplastic transformation and subsequent progression can facilitate efforts to define the biological basis for disease, improve prognostication of therapeutic response, and permit earlier tumor detection.
In addition, perinatal genetic problems frequently result from loss or gain of chromosome segments such as trisomy 21 or the micro deletion syndromes. Thus, methods of prenatal detection of such abnormalities can be helpful in early diagnosis of disease.
Cytogenetics is the traditional method for detecting amplified or deleted chromosomal regions. The resolution of cytogenetic techniques is limited, however, to regions larger than approximately 10 Mb (approximately the width of a band in Giemsa-stained chromosomes). In complex karyotypes with multiple translocations and other genetic changes, traditional cytogenetic analysis is of little utility because karyotype information cannot be fully interpreted. Furthermore conventional cytogenetic banding analysis is time consuming, labor intensive, and frequently difficult or impossible due to difficulties in obtaining adequate metaphase chromosomes. In addition, the cytogenetic signatures of gene amplification, homogeneously staining regions (HSR), or double minute chromosomes, do not provide any information that contributes to the identification of the sequences that are amplified.
More recent methods permit assessing the amount of a given nucleic acid sequence in a sample using molecular techniques. These methods (e.g., Southern blotting) employ cloned DNA or RNA probes that are hybridized to isolated DNA. Southern blotting and related techniques are effective even if the genome is heavily rearranged so as to eliminate useful karyotype information. However, these methods require use of a probe specific for the sequence to be analyzed. Thus, it is necessary to employ very many individual probes, one at a time, to survey the entire genome of each specimen, if no prior information on particular suspect regions of the genome is available.
Comparative genomic hybridization (CGH) is a more recent approach to detect the presence and identify the location of amplified or deleted sequences. See, Kallioniemi et al.,
Science
258: 818-821 (1992) and WO 93/18186). CGH reveals increases and decreases irrespective of genome rearrangement. In one implementation of CGH, genomic DNA is isolated from normal reference cells, as well as from test cells (e.g., tumor cells). The two nucleic acids are differentially labelled and then hybridized in situ to metaphase chromosomes of a reference cell. The repetitive sequences in both the reference and test DNAs are either removed or their hybridization capacity is reduced by some means. Chromosomal regions in the test cells which are at increased or decreased copy number can be quickly identified by detecting regions where the ratio of signal from the two DNAs is altered. For example, those regions that have been decreased in copy number in the test cells will show relatively lower signal from the test DNA than the reference compared to other regions of the genome. Regions that have been increased in copy number in the test cells will show relatively higher signal from the test DNA.
Thus, CGH discovers and maps the location of the sequences with variant copy number without prior knowledge of the sequences. No probes for specific sequences are required and only a single hybridization is required. Where a decrease or an increase in copy number is limited to the loss or gain of one copy of a sequence, the CGH resolution is usually about 5-10 Mb.
New techniques which provide increased sensitivity, more precise localization of chromosomal abnormalities and which can detect differences in levels of gene expression are particularly desirable for the diagnosis of disease. The present invention provides these and other benefits.
SUMMARY OF THE INVENTION
The present invention provides methods for quantitatively comparing copy numbers of at least two nucleic acid sequences in a first collection of nucleic acid molecules relative to the copy numbers of those same sequences in a second collection. The method comprises labeling the nucleic acid molecules in the first collection and the nucleic acid molecules in the second collection with first and second labels, respectively. The first and second labels should be distinguishable from each other. The probes thus formed are contacted to a plurality of target elements under conditions such that nucleic acid hybridization to the target elements can occur. The probes can be contacted to the target elements either simultaneously or serially.
Each target element comprises target nucleic acid molecules bound to a solid support. One or more copies of each sequence in a target element may be present. The sequence complexity of the target nucleic acids in the target element are much less than the sequence complexity of the first and second collections of labeled nucleic acids.
The nucleic acids for both the target elements and the probes may be, for example, RNA, DNA, or cDNA. The nucleic acids may be derived from any organism. Usually the nucleic acid in the target elements and the probes are from the same species.
The target elements may be on separate supports, such as a plurality of beads, or an array of target elements may be on a single solid surface, such as a glass microscope slide. The nucleic acid sequences of the target nucleic acids in a target element are those for which comparative copy number information is desired. For example, the sequence of an element may originate from a chromosomal location known to be associated with disease, may be selected to be representative of a chromosomal region whose association with disease is to be tested, or may correspond to genes whose transcription is to be assayed.
After contacting the probes to the target elements the amount of binding of each, and the binding ratio is determined for each target element. Typically the greater the ratio of the binding to a target element the greater the copy number ratio of sequences in the two probes that bind to that element. Thus comparison of the ratios among target elements permits comparison of copy number ratios of different sequences in the probes.
The methods are typically carried out using techniques suitable for fluorescence in situ hybridization. Thus, the first and second labels are usually fluorescent labels.
To inhibit hybridization of repetitive sequences in the probes to the target nucleic acids, unlabeled blocking nucleic acids (e.g., Cot-1 DNA) can be mixed with the probes. Thus, the invention focuses on the analysis of the non-repetitive sequences in a genome.
In a typical embodiment, one collection of probe nucleic acids is prepared from a test cell, cell population, or tissue under study; and the second collection of probe nucleic acids is prepared from a reference cell, cell population, or tissue. Reference cells can be normal non-diseased cells, or they can be from a sample of diseased tissue that serves as a standard for other aspects of the disease. For example, if the reference probe is genomic DNA isolated from normal cells, then the copy number of each sequence in that probe relative to the others is known (e.g., two copies of each autosomal sequence, and one or two copies of each sex chromosomal seque

Affiliated with

Also associated with

Rating

Comparative fluorescence hybridization to nucleic acid arrays does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Comparative fluorescence hybridization to nucleic acid arrays, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Comparative fluorescence hybridization to nucleic acid arrays will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3084395