Chromosomes and DNA-replication of rat kangaroo cells (PtK2)

The karyotype, chromosomal measurements, and the time course of DNA replication during the S-phase were determined in metaphase chromosomes of non-synchronized monolayer cultures of PtK₂ cells (CCL 56) derived from Potorous tridactylis. The karotype was the same as originally determined for this cell line. Chromosomal measurements differed from data for primary bone marrow cells of this species published by Shaw and Krooth. PtK₂ cells and chromosomes showed maximal incorporation of tritiated thymidine (³H-TdR) halfway through the S-phase. Chromosome Y₁ showed a second peak of ³H-TdR-incorporation at the end of the S-phase in addition to the peak halfway through S. Comparison of grain densities for chromosomal arms showed late replication of the short arms of chromosomes 1, 3, and X. The time course of incorporation of ³H-TdR was changed when cells were treated for 1 h with fluorodeoxyuridine (FUdR) prior to the ³H-TdR-pulse. FUdR-treated cells showed maximum incorporation of ³H-TdR immediately after the beginning of the S-phase, which was followed by a second peak halfway through the S-phase. This indicated that ³H-TdR-incorporation was partially synchronized by treatment of cells with FUdR. Total radioactivity of FUdR-treated cells had increased by 77% in comparison to cells not treated with FUdR, which indicates that approximately 44% of the TdR-precursors of the latter cells may have originated from cellular precursor pools.