CELL-SPECIFIC ORGANIZATION OF THE 5S RIBOSOMAL-RNA GENE-CLUSTER DNA LOOP DOMAINS IN SPERMATOZOA AND SOMATIC-CELLS

DNA in eucaryotic cells is organized into loop domains, ranging in siz e from 25 to 100 kb, that are attached at their bases to the structura l component of the nucleus termed the nuclear matrix. These DNA loop d omains have been shown to be important in the regulation of both DNA r eplication and RNA transcription, In this study we have compared the s tructural organization of the DNA loop domains of the 5S rRNA gene clu ster in sperm, liver, and brain nuclei in the Syrian golden hamster, T he individual loop domains were visualized by fluorescent in situ hybr idization to protamine (sperm)- and histone (somatic)-depleted nuclei, termed nuclear matrix halo preparations. We found that in sperm nucle i, the 5S rRNA gene cluster was organized into three small loop domain s that were approximately 48 kb each. In both types of somatic cell nu clei examined, the 5S rRNA gene cluster was organized into a single, m uch larger loop domain that was up to 480 kb in length. The data sugge st that at least some of the compaction that sperm DNA undergoes durin g spermiogenesis is mediated by the nuclear matrix independent of prot amine binding. Additionally, this sperm-specific DNA organization may be involved in the specific patterns of DNA replication and transcript ion of the paternal genome in the embryo.