Linking maternal and somatic 5S rRNA types with different sequence-specific non-LTR retrotransposons

Area of Science:

• Genomics
• Molecular Biology
• Developmental Biology

Background:

• 5S ribosomal RNA (rRNA) is essential for ribosome function.
• Some species exhibit distinct 5S rRNA types for oogenesis and adult tissues.
• Zebrafish present a unique model for studying differential 5S rRNA gene expression.

Purpose of the Study:

• To investigate the differential accumulation and genomic organization of 5S rRNA types in zebrafish.
• To explore the role of sequence variation and retrotransposons in regulating 5S rDNA copy number.
• To identify novel retrotransposon subfamilies associated with 5S rDNA loci.

Main Methods:

• Next-generation sequencing of zebrafish egg, embryo, and adult tissues.
• Comparative genomic analysis of maternal- and somatic-type 5S rDNA loci.
• Identification and characterization of Mutsu retrotransposon families and their target sites.

Main Results:

• Identified maternal-type 5S rRNA exclusively in oogenesis, replaced by somatic-type during embryogenesis.
• Maternal 5S rDNA has thousands of copies on chromosome 4; somatic has 12 copies on chromosome 18.
• Sequence variations in 5S rRNA genes correlate with TFIII and L5 binding, and define maternal/somatic MutsuDr retrotransposon subfamilies.
• Discovered four new maternal-type and two new somatic-type MutsuDr subfamilies with distinct target sequences.

Conclusions:

• Zebrafish exhibit distinct maternal and somatic 5S rRNA types with differential genomic organization.
• Sequence-specific retrotransposon integration by MutsuDr elements likely contributes to the differential copy number of 5S rDNA loci.
• Retrotransposon activity and associated small RNAs (piRNA) may play a role in regulating 5S rDNA locus evolution.