Repeated DNA Sequences in the Heterochromatic Y Chromosome of Adult Drosophila melanogaster

Abstract

DNA isolated from Drosophila melanogaster adults (XX, XY, XXY, XYY) was used in DNA-DNA hybridization experiments on nitrocellulose filters. Filter-bound DNA of "high-heterochromatin" flies (those with one or more Y chromosomes) is more effective in forming hybrid duplexes than is XX DNA. The quantitative difference in hybridization efficiency is due primarily to molecules with a relatively high thermal stability (duplexes that dissociate in the temperature range 8090°). Hybridization experiments with DNA samples that have been fractionated into reiterated and unique portions show that the majority of the hybrid duplexes formed involve reiterated DNA. A small, but highly specific, interaction of unique DNA sequences has also been detected in our experiments. These data indicate that a class of repeated DNA sequences is associated with the constitutive heterochromatin, specifically with the Y chromosome of D. melanogaster. Evidence is presented that this same class of molecules, or very similar ones, is to be found in other portions of the genome, presumably in X-chromosomal or centromeric heterochromatin.Recent reports (1-4) have demonstrated a marked capacity of the centromeric regions of Drosophila chromosomes to form hybrid molecules with complementary RNA (c-RNA) transcribed from the rapidly reassociating, repetitious portion of the genome. All of these reports have used the technique of in situ hybridization, developed within the past few years by workers in several different laboratories. We wish to report the results of a series of in vitro hybridization experiments that indicate that Drosophila melanogaster DNA isolated from "high-heterochromatin flies" (i.e., those with one or more Y chromosomes) contains more of a class of repeated DNA sequences than does DNA isolated from "low-heterochromatin" XX females. We have found that the repeated DNA sequences that form hybrid duplexes in our experiments can be derived from either XY or XX flies, and are, therefore, not exclusively Y chromosomal in origin. Finally, these experiments also show that it is possible to use DNA-DNA hybridization techniques on nitrocellulose filters to distinguish between DNA sequences isolated from the unique portion of the genome of D. melanogaster females (XX) and males (XY).D. melanogaster is uniquely suited for studies of the properties of heterochromatin and euchromatin. In this organism, as in no other, we have a wealth of knowledge about the cy-

The location of highly repetitious DNA in the somatic chromosomes of Drosophila melanogaster

“…The distribution of repeated DNA sequences has also been roughly correlated with the major blocks of heterochromatin in somatic cells (Gall et al, 1971). Other experimental approaches such as analytical centrifugation (Blumenfeld and Forrest, 1971) and filter hybridization (Perreault et al, 1973) have led to the, realization that the heterochromatic Y chromosome must be relatively rich in repeated DNA.…”

“…To what extent are repeated DNA sequences of one chromosome shared by other chromosomes ? It has been shown (Perreault et al, 1973;Sederoff et al, 1975) that Y chromosome DNA is capable of hybridizing with DNA derived from XX flies or cell lines. Also, recent studies by Peacock et al (1977) have shown that each of five satellite DNAs are found on all of the chromosomes of the D. melanogaster complement.…”