Hybridization of nucleic acids to chromosomes.

Abstract

Ever since the method of molecular hybridization of nucleic acids was conceived, a number of biologists have tried to hybridize labeled RNA or DNA to chromosomes for detection by autoradiography. The first report was by French and Kitzmiller (1967), who hybridized 3H-DNA from Drosophila melanogaster to the DNA of the salivary chromosomes of the same species in situ. Although their autoradiographs showed radioactivity on the chromosomes well above background, inconsistent results prevented them from publishing a full-length paper. In a second study by Gall and Pardue (1969) there were more complete and convincing findings using the oocytes of Xenopus. In this case, tritium labeled rRNA was found to bind to the rDNA of the nucleolus and to the extrachromosomal rDNA of free nucleoli. The hybridization methods were essentially similar to the nitrocellulose filter method of Gillespie and Spiegelman (1965). The labeled hybrid was unaffected by ribonuclease and unlabeled rRNA competed effectively against labeled rRNA for binding sites. A number of advances have been made in the last two years. We will report some new results, principally on hybridization to chromosomes of the various classes of 3H-RNA, and discuss the prospects of the cytological technique for the future. No attempt is made to review the literature but rather we will evaluate the methods as they can be applied to new and challenging experiments.