Genome organization in the human sperm nucleus studied by FISH and confocal microscopy

The sperm nucleus has a unique chromatin structure where the DNA is highly condensed and associated with specific proteins, the protamines. it is a no ndividing cell which is also transcriptionally inactive. After fusion with an oocyte, the sperm nucleus undergoes decondensation and, in the same time , starts replication and transcription. It has been suggested that somatic chromosomes during interphase are organized in territories which display a cell type and cell cycle specific distribution. The purpose of this work wa s to investigate whether chromosomes would also have a specific distributio n in the sperm nucleus, which could be related to its inactive state, and h ave implications on the early stages of fertilization. In the present study , centromeric and telomeric sequences were detected by fluorescent techniqu es performed on human decondensed spermatozoa. Chromosome painting probes w ere used to detect the chromosome X and chromosome 13 on interphase sperm n uclei. The fluorescent signals were captured in 3D with a confocal microsco pe. For each of these chromatin structures, the volume, position, and distr ibution of the signals were analyzed in samples of 30 nuclei with the help of image analysis software. The centromeres appeared grouped in several foc i that were randomly distributed within the sperm nucleus. The telomeres ga ve an approximately haploid number of small signals, evenly distributed thr oughout the nucleus. The chromosomes X and 13 occupied 4.7% and 3.7% of the total nuclear volume, respectively. Interestingly, the X chromosome territ ory showed a preferential position in the anterior half of the volume of th e nucleus, whereas chromosome 13 had a random position. This work shows a p articular distribution of chromosome territories in the human sperm nucleus that could be related to mechanisms implicated in its specific functions. The analysis of more chromosomes and chromosomal structures, including the Y chromosome, would help to understand the structure of the human sperm chr omatin, and its fundamental and clinical implications. Mol. Reprod. Dev. 55 :307-315, 2000. (C) 2000 Wiley-Liss, Inc.