Discovery of novel murine PML isoforms

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Promyelocytic leukemia protein (PML) is crucial for forming PML nuclear bodies (PML NBs), which are vital membraneless organelles.
• The specific roles of individual PML splicing variants are not well understood, especially in mouse models.
• Understanding PML isoform function is key to deciphering PML NB biology and associated cellular processes.

Purpose of the Study:

• To investigate the repertoire of murine PML isoforms expressed in mouse tissues and cells.
• To characterize the distinct properties and functions of different PML isoforms, including turnover kinetics and localization.
• To establish an isoform-resolved PML system for studying PML NB-associated processes.

Main Methods:

• Analysis of murine PML isoform expression in various mouse tissues and cells.
• Characterization of isoform-specific turnover kinetics at endogenous PML NBs.
• Assessment of de novo PML NB formation and degradation in PML-knockout cells upon arsenic exposure.
• Molecular dynamics simulations to predict isoform conformation and stability.
• Subcellular localization studies to determine enrichment in nucleoplasm or PML NBs.

Main Results:

• Identified canonical mPML1-3 and five predicted variants (mPMLX1, mPMLX2, mPMLX4-X6), plus a novel isoform, mPMLX7, with unique RBCC domain splicing.
• All identified PML isoforms exhibit distinct turnover rates within endogenous PML NBs.
• Except for mPMLX7, all isoforms can form PML NBs de novo in PML-knockout cells and are degraded by arsenic.
• Molecular dynamics simulations indicate mPMLX7 possesses a stable conformation and is enriched in the nucleoplasm, suggesting a specialized function.

Conclusions:

• The study comprehensively characterizes murine PML isoforms, revealing significant diversity in their expression, localization, and dynamics.
• The novel mPMLX7 isoform displays unique characteristics, including nucleoplasmic enrichment and resistance to de novo NB formation/degradation, pointing to specialized functions.
• This isoform-resolved PML system provides a valuable model for future research into the multifaceted roles of PML and PML NBs in cellular regulation.