An endogenous calcium oscillator may control early embryonic division

Area of Science:

• Developmental Biology
• Cell Cycle Regulation
• Biophysics

Background:

• Cell phase transitions in early embryonic development are linked to transient increases in cytosolic calcium ions ([Ca2+]i).
• These calcium dynamics suggest a role for intracellular calcium oscillations as a timing element in the embryonic "master clock."

Purpose of the Study:

• To investigate the hypothesis that a calcium ion ([Ca2+]i) oscillator is a fundamental component of the early embryonic master clock.
• To model the interaction between [Ca2+]i dynamics and the M-phase-promoting factor (MPF) cell cycle oscillator in sea urchin and Xenopus embryos.

Main Methods:

• Coupling a mathematical model of [Ca2+]i oscillations with an early embryonic cell cycle model based on MPF activity.
• Simulating distinct [Ca2+]i profiles (sharp transients vs. sinusoidal oscillations) observed in sea urchin and Xenopus embryos.
• Testing three hypothesized dynamical states of the MPF system under different [Ca2+]i oscillation conditions.

Main Results:

• [Ca2+]i oscillations can entrain an autonomous MPF oscillator (Hypothesis 1).
• [Ca2+]i oscillations can drive MPF activation cycles in excitatory and bistable MPF states (Hypotheses 2 and 3).
• Models incorporating [Ca2+]i as a timing element (Hypotheses 2 and 3) best explain key experimental observations in early embryonic division.

Conclusions:

• A [Ca2+]i oscillator is likely a fundamental timing element of the early embryonic master clock.
• The interplay between calcium signaling and MPF activity is crucial for regulating embryonic cell cycle progression.
• Further experiments are proposed to refine understanding of [Ca2+]i regulation and master clock components.