Absence of a measurable G2 phase in two Chinese hamster cell lines.

Abstract

Evidence is resented that demonstrates the absence of a measurable G2 prase in the cell cycles of two sublines of the Chinese hamster lung fibroblast V79. One of the sublines, in addition, lacks a detectable G1 phase, thereby possessing a cell cycle comprised of simply two phases, DNA synthesis (S) and mitosis (M).The cell life cycle of most mammalian cells can be described in terms of four phases (1): mitosis (M), a period between mitosis and the initiation of DNA replication (G1), DNA replication (S), and a period between the termination of DNA replication and the beginning of prophase (G2). [40][41][42][43][44][45][46][47][48][49][50] Ci/mmol, Amersham/Searle) for 15 min followed by a chase in complete medium plus 0.1 mM unlabeled thymidine. Samples for autoradiography were then taken at 0 min, 15 min, 30 min, 1 hr, 2 hr, and 3 hr after the pulse. The cells were trypsinized, treated with hypotonic solution (10 mM sodium citrate/30 mM potassium chloride) for 20 min followed by three 10-min cycles of fixation in methanol/glacial acetic acid (3:1), and dropped onto slides that had been dipped in H20 and either air-or flame-dried. The slides were coated with NTB2 emulsion, dried, exposed for 7-28 days, developed, and stained with crystal violet or Giemsa. The slides were then scored for % labeled nuclei and % labeled metaphases.An estimation of the length of the mitotic stages in V79-8 was obtained by examining living cells as they grew at 370 in flasks placed on the stage of an inverted phase contrast microscope. The first visible change in nuclear morphology (i.e., nuclear condensation as evidenced by a grainy appearance of the nucleoplasm) was considered the beginning of prophase. These cells were then monitored and their nuclear morphologies noted and recorded as a function of time. Observations of eight cells were used for estimating the mean length and range of prophase (i.e., initial condensation to the appearance of well-defined chromosomal bodies) and the total length of mitosis (i.e., from the onset of prophase until the apparent end of cytokinesis). RESULTSDetermination of Length of the G2 Phase. The strategy for determining the length of G2 for the two V79 cell lines was to subtract the length of prophase (measured by in situ observation) from the length of G2 + prophase. The average length of G2 + prophase was determined by pulse-labeling logarithmically growing cells with [3H]thymidine and preparing chromosome at intervals after the pulse. The time at which 50% of the metaphase cells are seen to be labeled was taken to be the average length of G2 + prophase (8). Results in Fig. 1

Additive neurogenesis supported by multiple stem cell populations mediates adult spinal cord development: A spatiotemporal statistical mapping analysis in a teleost model of indeterminate growth

“…This provides an upper bound of approximately 1.75 h for the duration of the G2 phase, after subtraction of the minimum BrdU incorporation time of roughly 15 min (Hayes and Nowakowski, ). The same upper bound also applies to the triple‐labeling time, under the assumption of no G2 phase [e.g., Liskay, ], yielding a maximum duration of 5.4 days for the division cycle. Conversely, assuming that the overlap in expression between the proliferation markers (PCNA and PH3) and BrdU is just long enough to allow BrdU incorporation (i.e., 15 min), a corresponding minimum duration of 20 h can be estimated for the division cycle.…”

Arrest states in a set of mutants of rat 3Y1 cells temperature‐sensitive for entering S phase

“…The concept of G1 phase is also obscure. Liscay (1977) reported that V79-8 cells, a subline of Chinese hamster lung fibroblast V-79, lack a detectable G1 phase. Okuda and Kimura (1982) proposed that the preparation for DNA synthesis in untransformed fibroblastic 3Y1 cells continues from the previous cycle.…”

Ribonucleotide Metabolism ‐ Fresh Approaches to Viral and Cancer Chemotherapy*

“…More information will be needed on the basal levels of Z '~' ( A )~ and their cores in both tumour cells and virally infected cells compared with normal cells; and on whether Ap4A is an alarmone, induced by the cellular stresses imposed, which might, among other things, cause the constituitive synthesis of elevated levels of Ap4A. A precedent for this is the finding of a subline of the Chinese hamster lung fibroblast V79 cell line which lacks a detectable G I and Gz phase (Liskay, 1977), and whose cell cycle therefore comprises two phases, DNA synthesis and mitosis; it is found to possess a constituitively high basal level of Ap4A (about 0 3 PM), even during mitosis (Weinmann-Dorsch et al, 1984).…”