Promyelocytic leukemia nuclear body-like structures can assemble in mouse oocytes

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Promyelocytic leukemia (PML) nuclear bodies (PML-NBs) are membrane-less organelles involved in diverse cellular functions.
• PML-NBs are typically found in somatic cells but are predicted to be absent in oocytes.
• The role of PML-NBs and their impact on SUMO protein dynamics in oocytes remains largely unexplored.

Purpose of the Study:

• To investigate the presence and function of PML-NBs in maturing oocytes.
• To determine the localization and behavior of PML protein and SUMO in oocytes.
• To elucidate the functional significance of a PML-NB-free environment in oocytes, particularly under stress conditions.

Main Methods:

• Immunofluorescence microscopy to visualize PML and SUMO protein localization in oocytes.
• Microinjection of human PML-encoding plasmids to induce PML-NB assembly in oocytes.
• Assessment of SUMO protein dynamics and localization under proteotoxic stress in the presence and absence of assembled PML-NBs.

Main Results:

• Endogenous PML protein was not detected in PML-NBs in maturing oocytes, but PML clients co-localized with SUMO in the nucleolus and peri-centromeric heterochromatin.
• In PML-NB-free oocytes, PML localized near chromatin and co-localized with SUMO around chromosomes during meiotic resumption.
• Assembled PML-NBs in oocytes consumed SUMO, sequestering it away from peri-centromeric heterochromatin during proteotoxic stress, thereby disturbing normal SUMO localization.

Conclusions:

• Oocytes maintain a PML-NB-free state, which is essential for preserving SUMO availability for critical cellular processes and stress responses.
• The absence of PML-NBs in oocytes facilitates the dynamic redistribution of SUMO protein, particularly during meiotic resumption and in response to stress.
• Deliberate assembly of PML-NBs in oocytes disrupts SUMO homeostasis, highlighting the importance of the natural PML-NB-free environment for oocyte health and function.