Lentiviral modification of enriched populations of bovine male gonocytes

Abstract

Undifferentiated germ cells have the capacity to develop into sperm capable of fertilizing oocytes and contributing genetic material to subsequent generations. The most primitive prepubertal undifferentiated germ cells include gonocytes and undifferentiated spermatogonia, including spermatogonial stem cells (SSC). Gonocytes, present in the testis at birth, differentiate into SSC, which maintain spermatogenesis for the remainder of the male's life. Because of their capacity to contribute to lifelong spermatogenesis, undifferentiated germ cells are attractive targets for genetic modification to produce transgenic animals, including cattle. To maximize the efficiency of genetic modification of bovine gonocytes and SSC, effective enrichment techniques need to be developed. Selection of bovine gonocytes using differential plating was improved 8-fold (P < 0.001) when using a combination of extracellular matrix proteins, including laminin, fibronectin, collagen type IV, and gelatin, compared to using laminin and gelatin alone. Selected cells labeled with PKH26 formed colonies of donor-derived germ cells after transplantation into recipient mouse testes, indicating putative stem cell function. Significantly more colonies (P < 0.001) per 1 × 105 viable transplanted cells were formed from isolated nonadherent cells (203 ± 23.2) compared to adherent (20 ± 2.7) or Percoll (45.5 ± 4.5) selected cells. After selection, some gonocytes were transduced using a lentiviral vector containing the transgene for the enhanced green fluorescent protein. Transduction efficiency was 17%. Collectively, these data demonstrate effective methods for the selection and genetic modification of bovine undifferentiated germ cells.