The Principles of Clinical Cytogenetics - Extra Materials - Springer

456 Daynna Wolff and Stuart Schwartz
Fig. 1. Schematic representation of the basic steps of the FISH procedure. Both the probe and chromosomal
target are heat denatured. Probe sequences hybridize to the complementary target sequences and nonspecific
binding is eliminated via stringent washing. The probe hybridization is detected with fluorescence microscopy.
widely used repetitive sequence probes are for the α-satellite sequences located at the centromeres
of human chromosomes. α-Satellite DNA is composed of tandemly repeated monomers;
thus, the sequences targeted by the probes are present in several hundreds or thousands of
copies, producing strong signals. Each chromosome’s α-satellite sequence (with the exception
of chromosomes 13 and 21 and chromosomes 14 and 22) is sufficiently divergent to allow for the
development of centromere-specific probes. These probes are particularly useful for the detection
of aneuploidy in both metaphase and interphase cells. In addition, α-satellite probes are
useful for the detection of acquired monosomy or trisomy in malignancies, such as trisomy 12 in
chronic lymphocytic leukemia or monosomy 7 or trisomy 8 in myeloid disorders (see Chapter 15).
Other types of repetitive sequences for which probes have been developed include the β-satellite
sequences (located in the short arms of the acrocentric chromosomes), “classical” satellite sequences
(found at various locations including the heterochromatic region of the Y chromosome), and
telomeric repeat sequences (TTAGGG) that mark the physical ends of each human chromosome.
These latter probes are not as routinely used in the clinical setting, but they are valuable for the
study of structural aberrations.
Whole chromosome probes (WCPs), also known as chromosome libraries or chromosome “painting”
probes, are composed of unique and moderately repetitive sequences from an entire chromosome
or chromosomal region. The generation of this type of probe requires that DNA from a particular
chromosome be isolated from the rest of the genome. This can be accomplished using flow sorting,
somatic cell hybrids containing a single human chromosome or area of a chromosome, or
microdissected chromosomes and subsequent amplification of the dissected DNA sequences via polymerase
chain reaction (PCR) (6). WCPs are commercially available for each human chromosome and
are most frequently used for the study of structural aberrations. For example, WCPs can be used to