Single-molecule imaging correlates decreasing nuclear volume with increasing TF-chromatin associations during...

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Zygotic genome activation (ZGA) is a critical transition in early embryogenesis, marking the start of transcription after a period of quiescence.
• Understanding how transcription factor (TF)-chromatin interactions dynamically change to facilitate ZGA is essential but remains largely unexplored.

Purpose of the Study:

• To quantitatively investigate the evolution of TF-chromatin interactions during early zebrafish development leading up to ZGA.
• To visualize and analyze the binding dynamics of specific TFs, TBP and Sox19b, in live embryos.

Main Methods:

• Utilized single molecule tracking in live zebrafish embryos with reflected light-sheet microscopy.
• Developed novel data acquisition and analysis methods to quantify TF binding kinetics and bound fractions during rapid cell cycles.
• Visualized fluorescently labeled TF species: mEos2-TBP and mEos2-Sox19b.

Main Results:

• Observed an increase in the chromatin-bound fraction of both TBP and Sox19b during early zebrafish development.
• The observed increase aligns with physical models incorporating decreasing nuclear volume and increasing DNA accessibility.
• Data suggests Sox19b's increased chromatin association is primarily driven by nuclear volume reduction.

Conclusions:

• Single molecule tracking provides quantitative insights into TF-chromatin dynamics around ZGA.
• Changes in TF-chromatin associations are significant during the developmental window encompassing ZGA.
• The study elucidates the physical mechanisms governing TF binding during early embryogenesis.