Specific patterns of differential condensation induced photochemically in human chromosomes

We have induced reproducible changes in the condensation cycle of human lymphocytic chromosomes, resulting in a characteristic pattern of thicker and narrower segments along the chromosome body. This effect was obtained by in vitro treatments of cultures with a hematoporphyrin derivative, earlier applied as a sensitizing agent in photodynamic cancer therapy. The new chromosomal phenotype shows similarities to the prosomization phenomenon, described previously by us in various tumours. We believe that the new technique, briefly presented here, will be useful to a number of biologic fields, including diagnostics of genic aberrations, both on the chromosomal and the molecular level. The unusually precise and clear-cut distinction among the elements of the novel chromosome phenotype will help pinpoint specific sites and facilitate in situ hybridization as well as harvesting of chromosome samples by microdissection for analysis of DNA and DNA-associated proteins.