Chromatin architecture transitions from zebrafish sperm through early embryogenesis

Area of Science:

• Genomics
• Developmental Biology
• Epigenetics

Background:

• 3D chromatin mapping reveals genome regulation.
• Zebrafish embryos show unique pre-zygotic genome activation (pre-ZGA) chromatin structure.

Purpose of the Study:

• Investigate zebrafish sperm chromatin architecture.
• Compare sperm chromatin to early embryonic chromatin structure.
• Understand chromatin formation post-ZGA.

Main Methods:

• Low-cell in situ Hi-C for higher-order architecture assessment.
• Chemical inhibition of Ep300a (p300) and Crebbpa (CBP) activity.

Main Results:

• Zebrafish sperm chromatin, histone-packaged, lacks TADs but has repeating "hinge-like" domains.
• Pre-ZGA zebrafish embryos lack chromosomal structure, contrary to previous reports.
• Post-ZGA, small contact domains (∼90 kb) form at enhancers, including super-enhancers.
• Inhibiting p300/CBP reduced H3K27ac and diminished these contacts, without affecting transcription.

Conclusions:

• Zebrafish sperm possess distinct histone-packaged chromatin structures.
• Initial high-order chromatin architecture in zebrafish embryos forms post-ZGA.
• Enhancers with high H3K27ac are crucial for early chromatin architecture formation.