Using fluorescence in situ hybridization, conventional epifluorescence
microscopy, and laser scanning confocal microscopy followed by three-
dimensional reconstruction we describe a well-defined higher order pac
kaging of the human genome in the sperm cell nucleus. This was determi
ned by the spatial localization of centromere and telomere regions of
all chromosomes and supported by localization of subtelomere sequences
of chromosome 3 and the entire chromosome 2. The nuclear architecture
in the human sperm is characterized by the clustering of the 23 centr
omeres into a compact chromocenter positioned well inside the nucleus.
The ends of the chromosomes are exposed to the nuclear periphery wher
e both the subtelomere and the telomere sequences of the chromosome ar
ms are joined into dimers. Thus chromosomes in the human sperm nucleus
are looped into a hairpin-like configuration. The biological implicat
ions of this nuclear architecture in spermatogenesis and male pronucle
ar formation following fertilization are discussed.