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Fig. 1 | Stem Cell Research & Therapy

Fig. 1

From: The cell cycle as a brake for β-cell regeneration from embryonic stem cells

Fig. 1

Differences in the cell cycle machinery of β cells (a) and undifferentiated embryonic stem (ES) cells (b). The cell cycle of ES cells is shortened relative to that of β cells. An abbreviated G1 phase is responsible for the difference in cell cycle length. a In β cells, mitogen signaling through the mitogen-activated protein kinase (MAPK) pathway activates CDK4–cyclin D kinase activity, thus hypophosphorylating retinoblastoma protein (pRB), which then leads to release of E2F, allowing it to activate transcription of genes necessary in the progression of the cell cycle. b In ES cells, mitogen signaling through the MAPK pathway seems to be irrelevant in the progression of cell cycle. Cyclin E–CDK2 expression is cell cycle-independent and constitutively active throughout the cell cycle, which allows the transition of ES cells from M phase directly to late G1. The resulting absence of the cyclin D-dependent early G1 phase shortens the G1 phase and the entire cell cycle. In beta cells, cyclin D–CDK4 is highly active but cyclin E–CDK2 is absent, making the cell cycle between these two cells highly different

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