PIWIL3 Forms a Complex with TDRKH in Mammalian Oocytes

Area of Science:

• Reproductive biology
• Molecular genetics
• Germ cell biology

Background:

• PIWI proteins are vital for genome integrity in germ cells.
• Human PIWIL3 lacks a direct mouse homologue, limiting research models.
• Bovine oocytes offer a unique model to study PIWIL3 function.

Purpose of the Study:

• To investigate the expression, localization, and interactions of PIWIL3 in bovine oocytes.
• To understand PIWIL3's role in germ cell genome maintenance.
• To identify PIWIL3-interacting proteins and associated small RNAs.

Main Methods:

• Immunofluorescence microscopy to localize PIWIL3 within oocytes.
• Co-immunoprecipitation assays to identify PIWIL3-interacting partners.
• RNA sequencing to profile piRNAs bound to the PIWIL3 complex.
• Site-directed mutagenesis to assess the role of PIWIL3 N-terminal arginines.

Main Results:

• PIWIL3 was localized to mitochondria in bovine oocytes.
• PIWIL3 expression is tightly regulated spatially and temporally.
• PIWIL3 forms a ternary complex with TDRKH and PNLDC1 in mitochondria.
• N-terminal arginines of PIWIL3 are crucial for complex formation.
• Approximately 50% of PIWIL3-associated piRNAs map to transposable elements.

Conclusions:

• PIWIL3 plays a critical role in safeguarding genome integrity in mammalian oocytes, particularly in regulating transposable elements.
• The mitochondrial localization and complex formation with TDRKH and PNLDC1 highlight a novel mechanism for PIWIL3 function.
• Bovine oocytes serve as a valuable model for studying PIWIL3, complementing studies in other species.