Mitochondrial selfish elements and the evolution of biological novelties

Area of Science:

• Mitochondrial genetics and evolution
• Bivalve reproductive biology
• Molecular mechanisms of sex determination

Background:

• Doubly uniparental inheritance of mitochondria (DUI) is observed in the Manila clam, *Ruditapes philippinarum*.
• Mitochondrial inheritance patterns are crucial for understanding evolutionary processes and reproductive strategies.
• The role of specific proteins in DUI and sex determination remains largely unexplored.

Purpose of the Study:

• To investigate the novel male-specific mitochondrial protein RPHM21 and its potential role in DUI.
• To analyze the characteristics and evolutionary origins of RPHM21 and its female counterpart, RPHF22.
• To propose a model for the emergence of DUI and gonochorism driven by selfish mitochondrial elements.

Main Methods:

• Review of existing data on *rphm21* transcription and translation.
• Comparative analysis of RPHM21 and RPHF22, including homology and polymorphism.
• Hypothesis formulation based on accumulated evidence and evolutionary principles.

Main Results:

• RPHM21 is a male-specific protein accumulating in spermatogenic cells.
• Evidence suggests a potential viral origin for RPHM21.
• RPHM21's activity during spermatogenesis may influence mitochondrial inheritance and sexual differentiation.

Conclusions:

• RPHM21 is a key candidate for mediating DUI and potentially driving the evolution of gonochorism from hermaphroditism.
• DUI systems may represent resolved conflicts involving selfish genetic elements, potentially involving mtDNA-encoded proteins.
• This study proposes DUI as a novel animal sex-determination system involving mitochondrial DNA.