Chromatin dynamics during epigenetic reprogramming in the mouse germ line.

Area of Science:

• Developmental Biology
• Epigenetics
• Cell Biology

Background:

• Germ cell lineage development involves totipotency generation.
• DNA demethylation and parental imprint erasure are critical events in mouse primordial germ cells (PGCs) around embryonic day 11.5.
• The mechanisms underlying PGC reprogramming remain largely unknown.

Purpose of the Study:

• To investigate the chromatin changes associated with DNA demethylation and imprint erasure in mouse PGCs.
• To understand the molecular mechanisms driving PGC reprogramming.

Main Methods:

• Analysis of chromatin modifications and histone variants in PGCs at different developmental stages (E8.5 and in gonads).
• Examination of histone chaperone accumulation (HIRA and NAP-1).
• Correlation of chromatin changes with genome-wide DNA demethylation.

Main Results:

• PGC chromatin reprogramming occurs in two distinct steps, starting with a pluripotency-like signature at E8.5.
• Major nuclear architecture changes, histone modification erasure, and histone variant exchange occur as PGCs enter the gonads.
• Histone chaperones HIRA and NAP-1 accumulate in PGCs undergoing reprogramming, suggesting a role in histone replacement.
• Chromatin changes are closely linked with genome-wide DNA demethylation.

Conclusions:

• Histone replacement is likely critical for the observed chromatin rearrangements during PGC reprogramming.
• The timing suggests histone replacement may be a response to DNA demethylation, potentially via a DNA repair-based mechanism, rather than a prerequisite.