LOCALIZATION OF 3 GENES IN THE HOOK-SHAPED HAMSTER SPERM NUCLEUS BY FLUORESCENT IN-SITU HYBRIDIZATION

We mapped the positions of three different genes in the flat, hook-sha ped hamster sperm nucleus to determine the specificity of sperm DNA po sitioning. The positions of the 5S rRNA gene cluster, the CAD gene, an d the class I 1.6 gene were determined by fluorescent in situ hybridiz ation (FISH) in over 50 hamster sperm nuclei for each gene. We first d emonstrated by FISH with mitotic chromosomes that the latter two genes were localized on the same chromosome. Within the sperm nuclei, we fo und that the precise position was variable for each of the three genes , but that there were two areas of preferred localization that contain ed 26-31% of the nuclear area and within which 80% of the signals were located. Nuclei were then hybridized to two genes simultaneously, usi ng either two genes located on the same chromosome or two genes locate d on different chromosomes. We found no preference for orientation of one gene relative to the other for either pair of genes examined. This suggested that the relative arrangements of chromosomes within the sp erm nucleus are flexible. These data demonstrate that the topographica l arrangements of genes within the hamster sperm nucleus have a limite d plasticity allowing for a relatively large range of possible localiz ation.