Fig. 2. Analysis of chromosomes carrying transgene arrays in different MEL subclones reveals a large transgene insertion and cytogenetic instability. FISH using the plasmid pPALZ8.8 (green in A-F, top; red in G) was carried out on metaphase spreads and counterstained for DNA (blue in A-F, top, and G; white in A-F, bottom, and J). (A) The predominant chromosome in PALZ39E cells. (B) Other forms found in PALZ39E. (C) The predominant chromosome in the PALZ39E subclone A9. (D) Other forms found in the A9 subclone. (E) Original PALZ39M chromosome. (F) PALZ39M chromosome found after more than 25 cell culture passages. (G-J) Part of a metaphase plate from the cell line PALZ39E showing the predominant transgene-carrying chromosome type (bottom) and a normal chromosome 12 (top). Arrows indicate the borders of the transgene array. (G) Multicolor overlay with transgene array in red, paint probe for mouse chromosome 12 in green and DNA counterstain in blue. White lines in the overlay separate individual chromosomes. The gray-scale images for the transgene array (H), the chromosome 12 paint (I) and the counterstain (J) are also shown.