Chromosomal in situ suppression hybridization of human gonosomes and autosomes and its use in clinical cytogenetics

DNA libraries from sorted human gonosomes were used selectively to
stain the X and Y chromosomes in normal and aberrant cultured human
cells by chromosomal in situ suppression (CISS-) hybridization. The
entire X chromosome was stained in metaphase spreads. Interphase
chromosome domains of both the active and inactive X were clearly
delineated. CISS-hybridization of the Y chromosome resulted in the
specific decoration of the euchromatic part (Ypter-q11), whereas
the heterochromatic part (Yq12) remained unlabeled. The stained
part of the Y chromosome formed a compact domain in interphase
nuclei. This approach was applied to amniotic fluid cells
containing a ring chromosome of unknown origin (47,XY; +r). The
ring chromosome was not stained by library probes from the
gonosomes, thereby suggesting its autosomal origin. The sensitivity
of CISS-hybridization was demonstrated by the detection of small
translocations and fragments in human lymphocyte metaphase spreads
after irradiation with 60Co-gamma-rays. Lymphocyte cultures from
two XX-males were investigated by CISS-hybridization with Y-library
probes. In both cases, metaphase spreads demonstrated a
translocation of Yp-material to the short arm of an X chromosome.
The translocated Y-material could also be demonstrated directly in
interphase nuclei. CISS-hybridization of autosomes 7 and 13 was
used for prenatal diagnosis in a case with a known balanced
translocation t(7;13) in the father. The same translocation was
observed in amniotic fluid cells from the fetus. Specific staining
of the chromosomes involved in such translocations will be
particularly important, in the future, in cases that cannot be
solved reliably by conventional chromosome banding alone.