182 In Vitro Derivation of Male Germ Cells from Bovine Bone Marrow-Derived Mesenchymal Stem Cells

Abstract

During the last few years, the in vitro derivation of germ cell lineages from stem cells has emerged as an exciting new strategy for obtaining mature gametes. In vitro gamete derivation technology has potential applications as an alternative method for dissemination of elite animal genetics, production of transgenic animals, and conservation of endangered species. Germ cell differentiation and gametogenesis is a complex process and potential of different stem cell donors (i.e. SSC, ESC, iPSC) for in vitro male germ cell derivation has been inconsistent. Mesenchymal stem cells (MSC) may be suitable candidates for in vitro gamete derivation considering their (1) plasticity that is not limited to mesodermal derivatives, (2) availability of abundant tissues sources for isolation, (3) high proliferative potential, (4) simple and inexpensive isolation, and (5) high potential for cell therapy, including autologous or allogenic transplantation. The present study aimed to induce differentiation of MSC isolated from bone marrow derived from bovine male fetuses (bfMSC) into the germ cell lineage using an in vitro approach based on the exogenous effect of retinoic acid (RA) and bone morphogenetic protein 4 (BMP4). Differentiation media consisted in control media (DMEM with high glucose plus 10% fetal bovine serum, 100 IU mL⁻¹ penicillin, 100 μg mL⁻¹ streptomycin, and 0.25 μg mL⁻¹amphotericin B) supplemented with RA (0.01, 0.1, or 1 µM) or BMP4 (10, 50, or 100 ng mL⁻¹). Cell samples were obtained from differentiating and control bfMSC cultures and analysed for expression of housekeeping genes β-ACTIN and GAPDH, pluripotent genes OCT4 and NANOG, germ cell genes FRAGILLIS, STELLA, and VASA, male germ cell genes DAZL, PIWIl2, and STRA8, and meiotic biomarker SCP3 by quantitative-PCR (Q-PCR). OCT4, NANOG, and DAZL were immunodetected in undifferentiated and differentiated bfMSC using flow-cytometry analysis. The mRNA expression of DAZL was activated by RA or BMP4 supplementation, although no differences (P > 0.05) were detected among different concentrations. DAZL and NANOG mRNA levels increased (P < 0.05) from Day 7 to Day 21 during supplementation of RA (0.1 μM). In comparison, DAZL mRNA levels increased (P < 0.05) at Day 14 during supplementation of BMP4 (100 ng). OCT4 and SCP3 mRNA levels were not affected by RA or BMP4 treatments. Transcripts of FRAGILLIS, STELLA, VASA, PIWIl2, and STRA8 were not detected in control or differentiated bfMSC. Higher (P < 0.05) percentages of undifferentiated bfMSC were positive for NANOG (80.6%) and OCT4 (83.4%). DAZL- and NANOG-positive cells were 2.1% and 2.9%, and 95.9% and 97.8% at Days 0 and 21 of RA treatment, respectively. Data indicated that expression of germ cell biomarker DAZL in bfMSC is activated and increased after in vitro supplementation of RA and BMP4. Moreover, NANOG mRNA levels were regulated by RA treatment. Similar levels of SCP3 mRNA expression suggest that differentiated bfMSC were not induced into meiosis. Thus, exposure of bfMSC to RA or BMP4 under in vitro conditions might induce an early stage of premeiotic germinal differentiation.