An autoregulatory cell cycle timer integrates growth and specification in chick wing digit development

Area of Science:

• Developmental Biology
• Cell Cycle Regulation
• Embryogenesis

Background:

• Understanding the timing of cell proliferation and growth during embryogenesis is crucial.
• The cell cycle's role as a timer in development is hypothesized but lacks mechanistic understanding.

Purpose of the Study:

• To elucidate the mechanisms of a cell cycle timer in the chick wing bud's polarising region.
• To investigate the roles of Sonic hedgehog (Shh) and Bone Morphogenetic Protein 2 (Bmp2) signaling pathways in regulating cell proliferation and digit specification.

Main Methods:

• Analysis of cell proliferation in chick wing bud explants under varying Shh and Bmp2 signaling conditions.
• Investigation of key cell cycle regulators, including Cyclin D2 and p27^kip1.
• Assessment of digit formation and identity following experimental manipulation of signaling pathways.

Main Results:

• Shh signaling stimulates proliferation via Cyclin D2, followed by inhibition through a Bmp2-p27^kip1 pathway in polarising region cells.
• Blocking Shh signaling leads to over-proliferation and extra digit formation, preventable by Bmp2 or D cyclin inhibition.
• Bmp2 application restores posterior digit identity in the absence of Shh, indicating its role in antero-posterior axis specification.

Conclusions:

• A novel cell cycle timer integrating growth and specification is described in the chick wing bud.
• This timer, involving Shh, Cyclin D2, Bmp2, and p27^kip1, precisely controls proliferation and digit identity.
• The findings have broad implications for understanding embryonic development across various tissues.