In vitro production of haploid sperm cells from male germ cells of foetal cattle

The purpose of this study was to isolate the foetal cattle male germ cells (mGCs) and then induce them into sperm cells. The mGCs were purified and enriched by a two-step plating method based on the different adherence velocities of mGCs and somatic cells. The percentage of the vasa and the c-kit positive cells were 95.34 ± 2.25% and 53.3 ± 1.03% by using flow cytometry analysis (FCA), respectively. In feeder-free culture system, the half-suspending cells appeared and formed a 16-cell rosary in medium after the mGCs were cultured for 6–8 days. On immunocytochemical staining during the second passage, some single cells adhering to the plate appeared to be both Oct-4 and α6-integrin positive. During the third passage, the mGCs were induced for 48 h by retinol acid (RA) on Sertoli cell-feeder layer, followed by 5–7 days culture in an RA-free medium. Some elongated sperm-like cells appeared in the medium at this stage. We found that the most effective concentration of RA for the inducement was 10–7 mol l−1 (P < 0.01). The haploid cells in suspension were identified by FCA. The elongated sperm-like cells showed proacrosome-like structure and the flagellum with fibre construct under electron microscopy. The mRNA of outer dense fibre-3 (ODF-3) and transcription protein-1 (TP-1) could be detected in the suspended cells by using reverse transcription polymerase chain reaction (RT-PCR). About 23.1% bovine oocytes could be activated to perform cleavage by intracytoplasmic injection with the sperm-like cells, but embryos did not further develop. Our investigation further demonstrated that foetal cattle mGCs could be induced in vitro into haploid sperm in the short term.