PRENATAL-DIAGNOSIS OF TRISOMY-21 USING INTERPHASE FLUORESCENCE IN-SITU HYBRIDIZATION OF POST-REPLICATED CELLS WITH SITE-SPECIFIC COSMID ANDCOSMID CONTIG PROBES
Iv. Soloviev et al., PRENATAL-DIAGNOSIS OF TRISOMY-21 USING INTERPHASE FLUORESCENCE IN-SITU HYBRIDIZATION OF POST-REPLICATED CELLS WITH SITE-SPECIFIC COSMID ANDCOSMID CONTIG PROBES, Prenatal diagnosis, 15(3), 1995, pp. 237-248
Interphase fluorescence in situ hybridization (FISH) with chromosome 2
1-specific cosmid clones was used to identify trisomy 21 in cultured a
nd uncultured amniotic cells. Two novel site-specific cosmid clones (r
egions 21q22 and 21qtel) were compared with a cosmid contig (Zheng et
al., 1992). Correct identification of chromosome 21 copy number was ma
de in 65-75 per cent of trisomic cells and in 70-75 per cent of normal
disomic cells by using all the tested probes. However, the chromosome
21-specific telomeric probe (cos 17F8) showed the best results due to
more intense and clearly visible hybridization. Utilization of a dire
ctly fluorophorated telomeric probe using Cy3-dCTP and FluorX-dCTP all
ows accurate detection of chromosome 21 in a fast 'one-step' FISH proc
edure on uncultured interphase nuclei. In addition, we compared the ef
ficacy of FISH analysis for the total population of interphase cells a
nd cells in the post-replication (late S, G2) periods of the cell cycl
e. Selective scoring of cells in the post-replicative period (showing
a pair of hybridization signals on each chromatid of the replicated in
terphase chromosome) increased the number of informative nuclei by up
to 95-97 per cent. This approach allows cells with overlapping chromos
omes, artificial double hybridization signals on separate chromatids i
n interphase chromosomes, background hybridization, and polyploid cell
s to be analysed. Application of directly labelled telomeric cosmid pr
obes and integral analysis of hybridized nuclei in the pre- and post-r
eplication periods of the cell cycle may help to further improve the p
renatal detection of trisomy 21.