Fertility Gene Introns Harbor Transposable Elements that Shape Y-Loop Architecture

Area of Science:

• Genomics
• Evolutionary Biology
• Molecular Biology

Background:

• Transposable elements (TEs) drive genome evolution but their integration into regulatory networks is unclear.
• In Drosophila male germline, TEs are highly expressed during spermatocyte stage, coinciding with Y chromosome giant fertility gene activation.
• Y-linked genes feature large introns rich in repetitive DNA, forming Y-loops crucial for gene regulation.

Purpose of the Study:

• Investigate the origin and regulation of highly expressed TEs in Drosophila male germline.
• Determine if TEs are independently transcribed or integrated into Y-linked gene transcripts.
• Explore the role of TEs in the evolution of Y-linked fertility genes and speciation.

Main Methods:

• RNA fluorescence in situ hybridization (FISH) to visualize TE transcripts.
• Targeting specific TEs (accord2, Juan, HMS Beagle) and Y-linked genes (kl-2, kl-3, kl-5).
• Genetic perturbation of Y-linked loci and disruption of RNA-processing factors.

Main Results:

• Multiple TEs are transcribed from introns of Y-linked fertility genes, localizing to specific Y-loops.
• TE transcripts are eliminated upon perturbation of Y-linked loci or RNA-processing factors, indicating co-transcription.
• TE composition and expression patterns associated with Y-loops vary significantly across Drosophila species.

Conclusions:

• TE sequences are embedded within Y chromosome-associated nascent transcripts, not independently transcribed.
• TEs within Y-linked introns may contribute to the rapid evolution of these genes and influence male fertility.
• TE turnover in Y-linked introns offers a mechanism for repetitive DNA to impact germline gene regulation and speciation.