LINE-1 (L1) lineages in the mouse

Area of Science:

• Evolutionary Biology
• Genomics
• Molecular Evolution

Background:

• Long Interspersed Nuclear Element-1 (LINE-1) retrotransposons are mobile genetic elements with significant roles in genome evolution.
• Previous studies identified distinct lineages of mouse LINE-1 elements, including L1Md4 and L1MdA2.

Purpose of the Study:

• To investigate the evolutionary origins and relationships of a newly identified mouse LINE-1 family, designated T(F).
• To determine the phylogenetic context of the T(F) family within the broader landscape of mouse LINE-1 evolution.
• To explore potential instances of horizontal gene transfer in LINE-1 evolution.

Main Methods:

• Phylogenetic analysis of sequences within the 3' portion of LINE-1 repeats.
• Comparative analysis of T(F) family sequences from Mus musculus domesticus with known LINE-1 families from other mouse species (Mus spretus, Mus spicilegus).
• Directed search using PCR to identify specific LINE-1 lineages.

Main Results:

• The T(F) family from M. m. domesticus is the terminal subfamily of the L1Md4 lineage.
• The L1Md4 lineage diverged from the L1MdA2 lineage approximately 1 million years ago (MYA).
• The T(F) family from M. m. domesticus shows a more recent divergence (0.5 MYA) from M. spretus LINE-1 families (Ms475, Ms7024), indicating horizontal transfer.
• A separate M. spretus A2 lineage joins the domesticus lineage at approximately 1 MYA, consistent with vertical inheritance.
• A novel Z family, associated with beige and med mutations, was identified branching from the L1Md4 lineage.

Conclusions:

• The T(F) family's recent divergence from M. spretus LINE-1 elements strongly suggests horizontal transfer, a significant finding for LINE-1 evolutionary dynamics.
• The discovery of the Z family provides insight into the genetic basis of specific mouse mutations.
• The T(F) family may exhibit reduced 3' end truncation compared to other LINE-1 elements, potentially impacting their propagation.