Genome-defence small RNAs exapted for epigenetic mating-type inheritance

Area of Science:

• Epigenetics
• Molecular Biology
• Genetics

Background:

• In Paramecium, transposable elements are deleted during macronuclear development.
• Small RNAs (scnRNAs) produced during meiosis target these deletions.

Purpose of the Study:

• To investigate the role of scnRNA-guided deletions in the maternal inheritance of mating types in Paramecium tetraurelia.
• To understand the genetic basis of mating type determination in Paramecium species.

Main Methods:

• Analysis of scnRNA-dependent DNA deletion mechanisms.
• Comparative genomics of mating type genes (mtA and mtB) in Paramecium species.

Main Results:

• scnRNA-guided excision of the mtA promoter determines mating type O in P. tetraurelia.
• Coding-sequence deletions in the mtB gene determine mating type O in P. septaurelia.
• Both mechanisms involve scnRNA-mediated gene regulation and epigenetic inheritance.

Conclusions:

• The scnRNA pathway is exapted for regulating cellular genes and mediating transgenerational epigenetic inheritance.
• Independently evolved mechanisms in Paramecium species highlight the adaptability of scnRNA-guided deletions.
• This study resolves the long-standing problem of maternal inheritance of mating types.