title: In situ nick-translation distinguishes between active and inactive X chromosomes.
abstract: Template-active regions of chromatin are structurally distinct from nontranscribing segments of the genome. Recently, it was suggested that the conformation of active genes which renders them sensitive to DNase I may be maintained even in fixed mitotic chromosomes. We have developed a technique of mitotic cell fixation and DNase I-directed nick-translation which distinguishes between active and inactive X chromosomes. We report here that Gerbillus gerbillus (rodent) female cells contain easily identified composite X chromosomes each of which includes the original X chromosome flanked by two characteristic autosomal segments. After nick-translation the active X chromosome in each cell is labelled specifically in both the autosomal and X-chromosomal regions. The inactive X chromosome is labelled only in the autosomal regions and in a small early replicating band within the late replicating 'original X' chromosome. Our technique opens the possibility of following the kinetics of X-chromosome inactivation and reactivation during embryogenesis, studying active genes in the inactive X chromosome and mapping tissue-specific gene clusters.
mesh_terms: D000818:Animals; D001345:Autoradiography; D001973:Bromodeoxyuridine; D004261:DNA Replication; D003850:Deoxyribonuclease I; D004706:Endodeoxyribonucleases; D005260:Female; D005849:Gerbillinae; D007621:Karyotyping; D008677:Metaphase; D008938:Mitosis; D014176:Protein Biosynthesis; D012730:Sex Chromosomes / Q000378:metabolism*; D013698:Templates, Genetic; D014316:Tritium; D014960:X Chromosome / Q000378:metabolism*
chemical_list: D014316:Tritium; D004706:Endodeoxyribonucleases; D003850:Deoxyribonuclease I; D001973:Bromodeoxyuridine