CYTOGENETIC AND CELL HYBRIDIZATION STUDIES WITH INSECT AND MAMMALIAN CELLS IN VITRO

Cytogenetic studies were performed on two established and transformed cell lines, UM-BGE-1 and UM-BGE-2, derived from Blattella germanica (L.), the German cockroach (2n = 24). Both lines were shown to have a modal chromosome number of 24, and considerable degrees of aneuploidy. A proportion of cells in each line show presumably diploid karyotypes, with 12 sets of pairable chromosomes. Other karyotypes are seen within the modal number. Both lines were shown to have structural abnormalities occurring. Double minute chromosomes, shown to be associated with the neoplastic state in mammalian systems, are present in both cell lines in low frequency. C-banding revealed similar patterns in the two lines. G- and Q-banding methods, while producing some degrees of longitudinal differentiation in the chromosomes, did not give totally satisfactory results. N-banding gave a pattern virtually identical to the C-band pattern. CsCl density gradient analysis of the DNA from the two cell lines indicates a distribution of DNA in the gradient that is both broad and symmetrical. That fact correlates with CsCl density gradient analysis of DNA from other Orthopteran species. No satellite peaks were found. The presence the relative mobilities of a number of enzyme systems in the two cell lines were also investigated. These were compared to isozyme patterns from B. germanica in vivo. Seven enzyme patterns were observed in the UM-BGE-1 cell line, and six in UM-BGE-2. While there were some similarities between the cell lines, the degree of disparity indicates differing responses to conditions in vitro. There were also many similarities between the isozyme patterns of the cell lines and those of B. germanica in vivo. Polyethylene glycol-mediated cell fusion experiments using UM-BGE-1 cells and a variety of other cell lines, insect as well as mammalian, indicated several patterns: (1) UM-BGE-1 cells and many of the other insect cell lines respond to polyethylene glycol-induced fusion in a manner similar to that observed in mammalian cells. (2) Individual cell lines show particular responses to polyethylene glycol, and no generalizations can be made regarding responses of insect cell lines to PEG. (3) A series of co-cultivations showed no spontaneous interspecific heterokaryons formed, indicating that successful interspecific, non-induced, cell fusion is an extremely rare event. Polynuclear homokaryons were found for all the cell types, though it cannot be stated conclusively that intraspecific fusion was responsible. (4) Treatment with PEG induced both an increase in the numbers of polynuclear homokaryons that were observed, and the formation of interspecific heterokaryons in low frequency. (5) These experiments indicate a preferential fusion mechanism between like cells. Clearly, UM-BGE-1 cells fuse more readily with each other than with cells from other lines when given a choice. Also, UM-BGE-1 cells fused 2-3X more often with cells from insect species than with CHO-K1, a mammalian cell line