Fusion between human and Drosophila melanogaster cells induced by polyethylene glycol.

Polyethylene glycol was used to induce interspecific somatic cell fusion between human fibroblasts (stock F6) and Drosophila melanogaster cells from established cell lines (Cl 82 and 11 P102), characterized by different ploidy levels. The present investigation defines some parameters for Drosophila cell fusion and interspecific fusion between Drosophila and human cells. The cytological analysis provided evidence of spontaneous as well as induced human-Drosophila heterokaryon formation. The presence in the same cell of two types of nuclei, distinguishable because of their different size and morphology, was confirmed autoradiographically by 3H-thymidine pre-labelling of Drosophila cells. Furthermore, the retained DNA synthetic activity and some examples of mitotic figures of both types of nuclei in the heterokaryons indicate the viability of the fused cells.

Induction of premature chromosome condensation in Drosophila melanogaster-rat heterokaryons.

After fusion mediated by polyethylene glycol (PEG) plus dimethyl sulfoxide (DMSO) between rat and Drosophila melanogaster cells cultured in vitro, the phenomenon of premature chromosome condensation (PCC) induced by mitotic rat chromosomes was detected in Drosophila nuclei. Exceptionally PCC was induced in rat nuclei but only in the presence of a very high ploidy level of Drosophila mitotic chromosomes. This provides further evidence of the lack of species specificity and of the effect of dosage of the PCC inducing factors, even among very distant species.

Interstrain heterochromatin polymorphisms in Drosophila melanogaster.

Neuroblast chromosomes of 16 Drosophila melanogaster laboratory stocks (15 wild type and 1 carrying the mutant vermillion) were carefully analyzed for Q-banding patterns and morphological characteristics, in all the mitotic phases. Two forms of intraspecific heterochromatin variations, involving three types of chromosomes, are described: 1) differences in the fluorescence pattern with regard to the Y chromosome and the centromeric heterochromatin of the pair II; 2) differences in the size of the heterochromatic segment of the X chromosome. An unambiguous evidence of such variants was obtained by comparing homologous chromosomes in the F1 hybrids, as well as in the F2 offspring, where differences in appearance of the heteromorphic chromosomes was readily identified as to the parental origin. The possible evolutionary significance and the usefulness of such cytologically detectable genetic differences between various strains, are considered.

Karyotypic evolution in an originally XY cell line of Drosophila melanogaster: a case of heterochromatin increase in vitro.

The cell line Ca of Drosophila melanogaster, characterized initially by a nearly diploid and normal male karyotype (XY), was used to study chromosomal variation over a period of 5 years of cultivation in vitro. Some general aspects of cell population dynamics which are in accordance with previous findings are pointed out. Various phenomena regarding chromosomal changes leading to karyotype polymorphism are outlined, with a particular emphasis being given to the sex chromosomes. Accordingly, with the aid of fluorescence analysis, some features of the Y and the X chromosomes providing evidence of an enlargement of the heterochromatin (due to addition and to saltatory replication) are described. Moreover, a case of variation in cell morphology accompanied by karyotypic changes was observed, as well as the emergence of a new cell subline of XX type derived from the original of XY type.