Tec3, a new developmentally eliminated DNA element in Euplotes crassus

Area of Science:

• Genetics
• Molecular Biology
• Ciliatology

Background:

• Euplotes crassus undergoes massive DNA elimination during macronuclear development, excising over 100,000 internal eliminated sequences (IESs).
• IESs include unique DNA sequences and transposable elements like Tec1 and Tec2.
• The mechanisms governing IES excision and their origins are not fully understood.

Purpose of the Study:

• To identify and characterize new transposable elements involved in DNA elimination in Euplotes crassus.
• To investigate the structural features and genomic location of the novel Tec3 transposon family.
• To explore the potential role of Tec3 elements in the IES excision process.

Main Methods:

• Micronuclear genome analysis and DNA sequencing.
• Identification and characterization of Tec3 transposon family members.
• Comparative analysis of Tec3 element structures and their relationship to IESs.
• Investigation of Tec3 excision during macronuclear development.

Main Results:

• A new class of transposons, designated Tec3, was discovered in the Euplotes crassus micronuclear genome, with 20-30 copies.
• Tec3 elements possess long inverted terminal repeats and encode a tyrosine-type recombinase.
• One Tec3 element (Tec3-1) is integrated within the RPL29 gene and is excised as a circular molecule during macronuclear development.
• A second Tec3 element (Tec3-2) lacks typical IES termini, suggesting different excision or origin mechanisms.

Conclusions:

• The Tec3 transposon family represents a novel component of the Euplotes crassus genome with potential implications for genome evolution.
• Some Tec3 elements are substrates for the IES excision machinery, indicating a link between transposon activity and developmental DNA elimination.
• The existence of Tec3 elements with varying terminal structures provides insights into the origins and diversification of mobile DNA in ciliates.