Culture of PNKT-4B cells at invasion permissive and restrictive temperatures. I. Chromosomal analysis.

PNKT-4B is an aneuploid cell line derived from a herpesvirus-induced renal adenocarcinoma of Rana pipiens that displays restricted invasion at 21 degrees C or cooler and invasion at 23 degrees C through 28 degrees C. Metaphase chromosomes obtained from subcultures (passages 297; 345-347) grown at 18 degrees C or 28 degrees C were Giemsa stained or N-banded with acidic silver nitrate. Cells grown at 18 degrees C displayed a modal chromosome number of 41, while 28 degrees C cultures displayed a modal number of 40. The distribution of the chromosomes suggests that the two temperatures may be allowing growth of different subclonal populations. N-banding of chromosomes at both temperatures revealed an increase of active nucleolar organizer regions (NORs) over normal frog tissues, 2/2N. Analysis of 200 N-banded spreads from cells grown at each temperature revealed modal numbers of 9 NORs/cell and modal numbers of 6 NOR-containing chromosomes/cell. Nine specific NOR-containing chromosomes were identified and scored. Similar distributions were observed at 18 degrees C and 28 degrees C. The data imply that the modal number of PNKT-4B has shifted since it was first described, 39, and differs at invasion-permissive and -restrictive temperatures. Increased numbers of active NORs and alterations of NOR-containing chromosomes imply an amplification of rDNA over the amount in normal frog.