Changes in chromatin accessibility ensure robust cell cycle exit in terminally differentiated cells

Area of Science:

• Cell Biology
• Developmental Biology
• Genetics

Background:

• Most cells exit the cell cycle upon terminal differentiation, entering a quiescent G0 state resistant to mitogenic signals.
• The DREAM complex typically represses cell cycle gene expression to initiate G0.
• However, alternative mechanisms ensure stable cell cycle exit when DREAM function is impaired.

Purpose of the Study:

• To investigate novel mechanisms that ensure robust cell cycle exit during terminal differentiation.
• To explore the role of chromatin accessibility changes in enforcing cell cycle arrest.
• To understand the interplay between cell cycle exit and terminal differentiation in Drosophila melanogaster wing development.

Main Methods:

• Chromatin accessibility assays (e.g., ATAC-seq) were used to profile changes at key cell cycle genes (cycE, e2f1, stg) during Drosophila wing development.
• Genetic manipulation was employed to disrupt cell cycle exit and observe effects on chromatin accessibility and gene expression.
• Analysis of binding sites for signaling pathway effectors (Yorkie, Notch) within regulatory regions.

Main Results:

• Chromatin accessibility decreases at pupal wing enhancers for cycE, e2f1, and stg during terminal differentiation.
• This chromatin closing correlates with robust cell cycle exit and refractoriness to mitogenic signals.
• Disruption of cell cycle exit did not affect chromatin accessibility at cell cycle genes but altered hormone-induced transcription factors.

Conclusions:

• Developmentally programmed changes in chromatin accessibility act as a cell cycle-independent timer to enforce cell cycle exit.
• This mechanism limits responses to mitogenic signaling and prevents aberrant cycling in differentiating tissues.
• A novel molecular link between cell cycle exit and terminal differentiation during metamorphosis is revealed.