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Changes in oscillatory dynamics in the cell cycle of early Xenopus laevis embryos.

Tsai TY, Theriot JA, Ferrell JE - PLoS Biol. (2014)

Bottom Line: Shortening the first cycle, by treating embryos with the Wee1A/Myt1 inhibitor PD0166285, resulted in a dramatic reduction in embryo viability, and restoring the length of the first cycle in inhibitor-treated embryos with low doses of cycloheximide partially rescued viability.The high ratio in the first cycle allows the period to be long and tunable, and decreasing the ratio in the subsequent cycles allows the oscillator to run at a maximal speed.Thus, the embryo rewires its feedback regulation to meet two different developmental requirements during early development.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California, United States of America ; Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America ; Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America.

ABSTRACT
During the early development of Xenopus laevis embryos, the first mitotic cell cycle is long (∼85 min) and the subsequent 11 cycles are short (∼30 min) and clock-like. Here we address the question of how the Cdk1 cell cycle oscillator changes between these two modes of operation. We found that the change can be attributed to an alteration in the balance between Wee1/Myt1 and Cdc25. The change in balance converts a circuit that acts like a positive-plus-negative feedback oscillator, with spikes of Cdk1 activation, to one that acts like a negative-feedback-only oscillator, with a shorter period and smoothly varying Cdk1 activity. Shortening the first cycle, by treating embryos with the Wee1A/Myt1 inhibitor PD0166285, resulted in a dramatic reduction in embryo viability, and restoring the length of the first cycle in inhibitor-treated embryos with low doses of cycloheximide partially rescued viability. Computations with an experimentally parameterized mathematical model show that modest changes in the Wee1/Cdc25 ratio can account for the observed qualitative changes in the cell cycle. The high ratio in the first cycle allows the period to be long and tunable, and decreasing the ratio in the subsequent cycles allows the oscillator to run at a maximal speed. Thus, the embryo rewires its feedback regulation to meet two different developmental requirements during early development.

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Shortening of the first cycle period significantly reduces embryo viability, and cycloheximide rescues viability.(A–C) Application of PD0166285 during the first cycle causes a loss of viability, whereas later treatment does not. (A) Changes in the length of the first cycle in response to two concentrations of PD0166285. (B) Kaplan–Meier survival curves. (C) Survival at 44 h postfertilization. The data in (A) and (C) are from four experiments, whereas the data in (B) are from one representative experiment. (D–F) Cycloheximide (CHX, 0.25 µg/mL) partially rescues the effects of PD0166285 (30 µM) on viability. (D) Changes in the length of the first cycle in response to PD0166285 ± CHX. (E) Kaplan–Meier survival curves. (F) Survival at 44 h postfertilization. The data in (D) and (F) are from four experiments, whereas the data in (E) are from one representative experiment. (G) Photographs of drug-treated and control embryos at various times after fertilization. The embryos were placed in the same petri dish after the inhibitors were washed out at the completion of the first cycle. The arrows designate three PD-treated embryos that have discoordinated cell divisions as early as a few hours postfertilization; the other PD-treated embryos are grossly normal until the midblastula transition (bottom panel). The incubation temperature was 18° for the experiments in (A–F), and 23° for the experiment in (G).
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pbio-1001788-g007: Shortening of the first cycle period significantly reduces embryo viability, and cycloheximide rescues viability.(A–C) Application of PD0166285 during the first cycle causes a loss of viability, whereas later treatment does not. (A) Changes in the length of the first cycle in response to two concentrations of PD0166285. (B) Kaplan–Meier survival curves. (C) Survival at 44 h postfertilization. The data in (A) and (C) are from four experiments, whereas the data in (B) are from one representative experiment. (D–F) Cycloheximide (CHX, 0.25 µg/mL) partially rescues the effects of PD0166285 (30 µM) on viability. (D) Changes in the length of the first cycle in response to PD0166285 ± CHX. (E) Kaplan–Meier survival curves. (F) Survival at 44 h postfertilization. The data in (D) and (F) are from four experiments, whereas the data in (E) are from one representative experiment. (G) Photographs of drug-treated and control embryos at various times after fertilization. The embryos were placed in the same petri dish after the inhibitors were washed out at the completion of the first cycle. The arrows designate three PD-treated embryos that have discoordinated cell divisions as early as a few hours postfertilization; the other PD-treated embryos are grossly normal until the midblastula transition (bottom panel). The incubation temperature was 18° for the experiments in (A–F), and 23° for the experiment in (G).

Mentions: Finally, we asked whether a slow first cycle is important for proper embryonic development. To this end, we inhibited Wee1 and Myt1 with PD0166285 during the first cycle only and observed the developmental consequences. PD0166285 treatment decreased the period of the first cycle by 10 min (Figure 7A; see also Figure 3A). At the conclusion of the first cycle, the PD0166285 was washed out and the survival of the embryos was recorded through the tadpole stage. Most of the PD0166285-treated embryos completed the early embryonic cell cycles without problem, but viability dropped significantly at the midblastula transition (Figure 7B) and less than 1% of the embryos successfully developed into tadpoles (Figure 7C). In contrast, embryos treated with PD0166285 for the same duration after completion of the first cycle developed normally, indicating that the PD0166285-mediated effect was specific to the first cycle (Figure 7B,C).


Changes in oscillatory dynamics in the cell cycle of early Xenopus laevis embryos.

Tsai TY, Theriot JA, Ferrell JE - PLoS Biol. (2014)

Shortening of the first cycle period significantly reduces embryo viability, and cycloheximide rescues viability.(A–C) Application of PD0166285 during the first cycle causes a loss of viability, whereas later treatment does not. (A) Changes in the length of the first cycle in response to two concentrations of PD0166285. (B) Kaplan–Meier survival curves. (C) Survival at 44 h postfertilization. The data in (A) and (C) are from four experiments, whereas the data in (B) are from one representative experiment. (D–F) Cycloheximide (CHX, 0.25 µg/mL) partially rescues the effects of PD0166285 (30 µM) on viability. (D) Changes in the length of the first cycle in response to PD0166285 ± CHX. (E) Kaplan–Meier survival curves. (F) Survival at 44 h postfertilization. The data in (D) and (F) are from four experiments, whereas the data in (E) are from one representative experiment. (G) Photographs of drug-treated and control embryos at various times after fertilization. The embryos were placed in the same petri dish after the inhibitors were washed out at the completion of the first cycle. The arrows designate three PD-treated embryos that have discoordinated cell divisions as early as a few hours postfertilization; the other PD-treated embryos are grossly normal until the midblastula transition (bottom panel). The incubation temperature was 18° for the experiments in (A–F), and 23° for the experiment in (G).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3921120&req=5

pbio-1001788-g007: Shortening of the first cycle period significantly reduces embryo viability, and cycloheximide rescues viability.(A–C) Application of PD0166285 during the first cycle causes a loss of viability, whereas later treatment does not. (A) Changes in the length of the first cycle in response to two concentrations of PD0166285. (B) Kaplan–Meier survival curves. (C) Survival at 44 h postfertilization. The data in (A) and (C) are from four experiments, whereas the data in (B) are from one representative experiment. (D–F) Cycloheximide (CHX, 0.25 µg/mL) partially rescues the effects of PD0166285 (30 µM) on viability. (D) Changes in the length of the first cycle in response to PD0166285 ± CHX. (E) Kaplan–Meier survival curves. (F) Survival at 44 h postfertilization. The data in (D) and (F) are from four experiments, whereas the data in (E) are from one representative experiment. (G) Photographs of drug-treated and control embryos at various times after fertilization. The embryos were placed in the same petri dish after the inhibitors were washed out at the completion of the first cycle. The arrows designate three PD-treated embryos that have discoordinated cell divisions as early as a few hours postfertilization; the other PD-treated embryos are grossly normal until the midblastula transition (bottom panel). The incubation temperature was 18° for the experiments in (A–F), and 23° for the experiment in (G).
Mentions: Finally, we asked whether a slow first cycle is important for proper embryonic development. To this end, we inhibited Wee1 and Myt1 with PD0166285 during the first cycle only and observed the developmental consequences. PD0166285 treatment decreased the period of the first cycle by 10 min (Figure 7A; see also Figure 3A). At the conclusion of the first cycle, the PD0166285 was washed out and the survival of the embryos was recorded through the tadpole stage. Most of the PD0166285-treated embryos completed the early embryonic cell cycles without problem, but viability dropped significantly at the midblastula transition (Figure 7B) and less than 1% of the embryos successfully developed into tadpoles (Figure 7C). In contrast, embryos treated with PD0166285 for the same duration after completion of the first cycle developed normally, indicating that the PD0166285-mediated effect was specific to the first cycle (Figure 7B,C).

Bottom Line: Shortening the first cycle, by treating embryos with the Wee1A/Myt1 inhibitor PD0166285, resulted in a dramatic reduction in embryo viability, and restoring the length of the first cycle in inhibitor-treated embryos with low doses of cycloheximide partially rescued viability.The high ratio in the first cycle allows the period to be long and tunable, and decreasing the ratio in the subsequent cycles allows the oscillator to run at a maximal speed.Thus, the embryo rewires its feedback regulation to meet two different developmental requirements during early development.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, California, United States of America ; Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America ; Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America.

ABSTRACT
During the early development of Xenopus laevis embryos, the first mitotic cell cycle is long (∼85 min) and the subsequent 11 cycles are short (∼30 min) and clock-like. Here we address the question of how the Cdk1 cell cycle oscillator changes between these two modes of operation. We found that the change can be attributed to an alteration in the balance between Wee1/Myt1 and Cdc25. The change in balance converts a circuit that acts like a positive-plus-negative feedback oscillator, with spikes of Cdk1 activation, to one that acts like a negative-feedback-only oscillator, with a shorter period and smoothly varying Cdk1 activity. Shortening the first cycle, by treating embryos with the Wee1A/Myt1 inhibitor PD0166285, resulted in a dramatic reduction in embryo viability, and restoring the length of the first cycle in inhibitor-treated embryos with low doses of cycloheximide partially rescued viability. Computations with an experimentally parameterized mathematical model show that modest changes in the Wee1/Cdc25 ratio can account for the observed qualitative changes in the cell cycle. The high ratio in the first cycle allows the period to be long and tunable, and decreasing the ratio in the subsequent cycles allows the oscillator to run at a maximal speed. Thus, the embryo rewires its feedback regulation to meet two different developmental requirements during early development.

Show MeSH
Related in: MedlinePlus