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Tissue-specific expression of human provirus ERV3 mRNA in human placenta: two of the three ERV3 mRNAs contain human

N Kato, S Pfeifer-Ohlsson, M Kato

    Journal of Virology
    |July 1, 1987
    PubMed

    Insights

    Human endogenous retrovirus 3 (ERV3) produces abundant spliced mRNAs in the placenta. These transcripts lack key retroviral genes, suggesting ERV3 integrated near a cellular gene in early human ancestors.

    Area of Science:

    • Molecular Biology
    • Genomics
    • Virology

    Background:

    • Human endogenous retroviruses (HERVs) are remnants of ancient retroviral infections integrated into the host genome.
    • ERV3 is a specific HERV family with transcripts detected in placental tissues.
    • Understanding HERV transcription and structure is crucial for deciphering their role in human biology and evolution.

    Purpose of the Study:

    • To characterize the structure and transcription pattern of abundant ERV3-specific mRNAs found in human placental chorion.
    • To investigate the implications of ERV3 mRNA structure for its genomic integration and potential functional role.

    Main Methods:

    • Northern blot analysis to determine RNA size and abundance.
    • S1 nuclease mapping to precisely map the transcription start sites and splice junctions of ERV3 mRNAs.
    • Analysis of proviral sequence and long terminal repeat (LTR) regions.

    Main Results:

    • Three abundant polyadenylated ERV3 mRNAs (9, 7.3, and 3.5 kb) were identified in placental chorion mRNA.
    • All three ERV3 mRNAs are spliced and significantly truncated, lacking the gag gene and most of the pol gene.
    • Unlike typical retroviruses, no genome-length ERV3 mRNA was detected.
    • Two larger ERV3 mRNAs exhibited unusual splicing beyond the 3' LTR polyadenylation site, suggesting integration adjacent to a cellular gene.

    Conclusions:

    • ERV3 transcription in the placenta yields spliced, truncated mRNAs, deviating from canonical retroviral expression patterns.
    • The unique splicing of larger ERV3 mRNAs strongly implies that the ERV3 provirus integrated within or near a host cellular gene.
    • These findings provide insights into the expression of endogenous retroviruses and their genomic context in humans.

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