Retrotransposon expression and incorporation of cloned human and mouse retroelements in human spermatozoa

Fertil Steril. 2017 Mar;107(3):821-830. doi: 10.1016/j.fertnstert.2016.12.027. Epub 2017 Jan 27.


Objective: To investigate the expression of long interspersed element (LINE) 1, human endogenous retrovirus (HERV) K10, and short interspersed element-VNTR-Alu element (SVA) retrotransposons in ejaculated human spermatozoa by means of reverse-transcription (RT) polymerase chain reaction (PCR) analysis as well as the potential incorporation of cloned human and mouse active retroelements in human sperm cell genome.

Design: Laboratory study.

Setting: University research laboratories and academic hospital.

Patient(s): Normozoospermic and oligozoospermic white men.

Intervention(s): RT-PCR analysis was performed to confirm the retrotransposon expression in human spermatozoa. Exogenous retroelements were tagged with a plasmid containing a green fluorescence (EGFP) retrotransposition cassette, and the de novo retrotransposition events were tested with the use of PCR, fluorescence-activated cell sorting analysis, and confocal microscopy.

Main outcome measure(s): Retroelement expression in human spermatozoa, incorporation of cloned human and mouse active retroelements in human sperm genome, and de novo retrotransposition events in human spermatozoa.

Result(s): RT-PCR products of expressed human LINE-1, HERV-K10, and SVA retrotransposons were observed in ejaculated human sperm samples. The incubation of human spermatozoa with either retrotransposition-active human LINE-1 and HERV-K10 or mouse reverse transcriptase-deficient VL30 retrotransposons tagged with an EGFP-based retrotransposition cassette led to EGFP-positive spermatozo; 16.67% of the samples were positive for retrotransposition. The respective retrotransposition frequencies for the LINE-1, HERV-K10, and VL30 retrotransposons in the positive samples were 0.34 ± 0.13%, 0.37 ± 0.17%, and 0.30 ± 0.14% per sample of 10,000 spermatozoa.

Conclusion(s): Our results show that: 1) LINE-1, HERV-K10, and SVA retrotransposons are transcriptionally expressed in human spermatozoa; 2) cloned active retroelements of human and mammalian origin can be incorporated in human sperm genome; 3) active reverse transcriptases exist in human spermatozoa; and 4) de novo retrotransposition events occur in human spermatozoa.

Keywords: HERV-K10; LINE-1; human spermatozoa; retroelements; retrotransposition.

MeSH terms

  • Animals
  • Cell Separation / methods
  • Cloning, Molecular*
  • Endopeptidases / biosynthesis
  • Endopeptidases / genetics*
  • Flow Cytometry
  • Gene Expression Regulation
  • Genes, Reporter
  • Green Fluorescent Proteins / biosynthesis
  • Green Fluorescent Proteins / genetics
  • Humans
  • Long Interspersed Nucleotide Elements*
  • Male
  • Mice
  • Microscopy, Confocal
  • Minisatellite Repeats*
  • Oligospermia / genetics*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Spermatozoa / metabolism*
  • Transcription, Genetic
  • Transfection
  • Viral Proteases


  • enhanced green fluorescent protein
  • Green Fluorescent Proteins
  • Endopeptidases
  • Viral Proteases
  • human endogenous retrovirus K10 protease