Mouse endogenous retroviruses can trigger premature transcriptional termination at a distance

Transcriptional termination occurs between alleles in F₁ and F₂ mice. (A, top) Northern blot demonstrating differential reduction in full-length transcripts in brains from CAST × B6 but not B6 × CAST F₁ hybrid with heterozygous ERV integrants. In contrast, truncated transcripts (arrows) are detected in both lineages. (Bottom) Loading control showing 28S and 18S rRNA. Comparable amounts (10 mcg) of total RNA were loaded in each lane. (B) Quantitative RT-PCR assay for full-length transcripts (extending past exon 7) in brains from various mouse strains. Results are expressed as the fold change in levels relative to the sample with the lowest concentration. (C) Quantitative RT-PCR assay for the 3′ end of prematurely truncated transcripts shows that their expression is boosted specifically in strains containing ERV_Slc15a2. (D) Quantitative RT-PCR assays for full-length and prematurely terminated transcripts (each in duplicate or triplicate) in individual mice with indicated genotypes. Results were normalized to Hprt (i.e., hypoxanthine guanine phosphoribosyl transferase) transcript expression. (Error bars) Range of data. Numbers at top are identifiers for individual mice (Supplemental Table 3).