Table 1.
Examples of interlinked positive feedback loops in biological regulation.
| System | Positive feedback loops | References |
|---|---|---|
| Mitotic trigger | Cdc2 → Cdc25 → Cdc2 Cdc2 -| Wee1 -| Cdc2 Cdc2 -| Myt1 -| Cdc2 |
(12, 13) |
| p53 regulation | p53 → PTEN -| Akt → Mdm-2 -| p53 p53 → p21 -| CDK2 -| Rb -|Mdm-2 -| p53 |
(14) |
| Xenopus oocyte maturation | Cdc2 → Mos → Cdc2 Cdc2 → Cdc25 → Cdc2 Cdc2 → Myt1 → Cdc2 |
(11) |
| Budding yeast traversal of START | Cdc28 → Cln transcription → Cdc28 Cdc28 -| Sic1 -| Cdc28 |
(15) |
| Budding yeast polarization | Cdc42 → Cdc24 → Cdc42 Cdc42 → actin → Cdc42 |
(6, 16, 17) |
| Eukaryotic chemotaxis | PIP3 → Rac/Cdc42 → PIP3 PIP3 → Rac/Cdc42 → actin → PIP3 |
(18) |
| Muscle cell fate specification | MyoD → MyoD Myogenin → myogenin MyoD → CDO → MyoD MyoD → Akt2 → MyoD |
(19–21) |
| B cell fate specification | IL-7 → EBF → IL-7 EBF -| Notch-1 -|E2A → EBF → Pax-5 -| Notch-1 -| E2A→ EBF |
(22, 23) |
| Notch/delta signaling | Notch (cell A) -| Delta (cell A) -| Notch (cell A) Notch (cell A) -| Delta (cell A) → Notch (cell B) -| Delta (cell B) → Notch (cell A) |
(24) |
| EGF receptor signaling | EGFR -| PTP -| EGFR Sos → Ras → Sos ERK2 → arachidonic acid → ERK2 EGFR → sheddases → EGFR |
(25–28) |
| S. cerevisiae galactose regulation | Gal2 → galactose -| Gal80 -| Gal2 Gal3 -| Gal80 -| Gal3 |
(29) |
| Blood clotting | thrombin → Xa:Va → thrombin XIIa → XIIa IXa:VIIIa → Xa → IXa:VIIIa |
(30) |
| Platelet activation | activation → ADP secretion → activation activation → 5-HT secretion → activation activation → TxA2 secretion → activation activation → aggregation → activation |
(31) |
| Ca2+ spikes/oscillations | Ca2+cyt → PLC → IP3 → Ca2+cyt Ca2+cyt → IP3R → Ca2+cyt Ca2+cyt → IP3R -| Ca2+ER -| SOC → Ca2+cyt |
(7, 8) |
ADP, adenosine 5′-diphosphate; CDK, cyclin-dependent kinase; cyt, cytochrome; CDO, a component of a cell surface receptor; EGFR, epidermal growth factor receptor; ER, endoplasmic reticulum; 5-HT, serotonin (5-hydroxytryptamine); IL-7, interleukin-7; IP3R, inositol 1,4,5-trisphosphate receptor; PIP3, phosphatidylinositol 3,4,5-trisphosphate; PLC, phospholipase C; PTEN, phosphatase and tensin homolog deleted on chromosome 10; PTP, protein tyrosine phosphatase; S. cerevisiae, Saccharomyces cerevisiae; TxA2, thromboxane A2.