Bistability in the JNK cascade

Area of Science:

• Cellular signaling pathways
• Biochemistry of cell cycle regulation
• Developmental biology

Background:

• Signaling proteins can exhibit complex properties like adaptation and bistability.
• The JNK cascade is a well-studied signaling system.
• Xenopus laevis oocytes are suitable for quantitative cell signaling analysis.

Purpose of the Study:

• To quantitatively assess JNK cascade responses to physiological (progesterone) and pathological (sorbitol) stimuli in Xenopus oocytes.
• To determine if JNK responses are graded, ultrasensitive, or bistable.
• To investigate the role of feedback mechanisms in JNK signaling.

Main Methods:

• Experimental assessment of JNK activity in Xenopus oocytes.
• Stimulation with progesterone and hyperosmolar sorbitol.
• Quantitative analysis of JNK response characteristics.

Main Results:

• JNK responses to both stimuli were essentially all-or-none, with few intermediate activity levels.
• JNK activation was autocatalytic, indicating a positive feedback loop.
• JNK displayed hysteresis in response to sorbitol, demonstrating biochemical memory.

Conclusions:

• JNK signaling in Xenopus oocytes functions as a bistable system, characterized by all-or-none responses, positive feedback, and hysteresis.
• Bistability is a common feature in oocyte maturation and embryogenesis, seen in other pathways like Mos/MEK/p42 MAPK and Cdc2/cyclin B.
• Evolution has repeatedly favored bistability for generating digital responses in biological systems.