Male haploid cells through direct spherification

Abstract

To obtain de novo male gametes capable of inducing full preimplantation blastocyst development using a novel three-dimensional (3D) culture system. Mouse embryonic stem cells (mESCs) were spherified by plunging in sodium alginate followed by calcium chloride, delineating a 3D environment that simulates the seminiferous tubule. As a control, mESCs cultured on two-dimensional plates were used. Plates and spheres containing mESCs from both methods were exposed to Activin-A, bFGF, and KSR followed by exposure to BMP4, LIF, SCF, and EGF to promote differentiation into male germ-like cells. Cells were assessed for VASA, DAZL, and BOULE on days 3 and 10. Cells were later injected into activated oocytes and monitored using time-lapse imaging on days 15, 22, 29, and 36. Control conceptuses generated using mature epididymal spermatozoa were also monitored via time-lapse imaging. On day 3, cells differentiated on plates expressed VASA at 1% and DAZL at 29%. In spheres, VASA was expressed at a rate of 15% and DAZL at a rate of 45% (P<.001). On day 10, cells differentiated on plates had VASA expression of 7%, DAZL of 23%, and BOULE of only 0.5%. Cells differentiated into spheres expressed VASA at a rate of 20%, DAZL at 43%, and BOULE at 10% (P<.001). Subsequent differentiation in spheres on day 3 exhibited a DAZL (expressed in spermatogonia) expression of 43% and a VASA (further spermatogenesis progression) expression of 15%. On day 10, DAZL and VASA expressions were reassessed and increased to 45% and 18%, respectively. BOULE, a marker expressed solely in postmeiotic spermatocytes, was expressed at 8%, whereas acrosin was expressed in spermatids at 2%. On day 15, VASA expression plateaued at 17%, BOULE peaked at 10%, and acrosin reached 5%. On day 22, expression of VASA increased to 19%, BOULE decreased to 8%, and acrosin peaked at 7%. On day 29, VASA expression peaked at 20%, BOULE dropped to 2%, and acrosin remained stable at 7%. On day 36, VASA expression remained at 13%, whereas BOULE and acrosin expression decreased to 0% and 1%, respectively. The control cohort attained 88.4% fertilization and 76.9% blastocyst rates. De novo gametes achieved fertilization rates of 35.0%, 61.1%, 81.8%, and 50.0% on days 15, 22, 29, and 36, respectively. Neogametes-generated blastocyst rates were 5.0%, 16.7%, 36.4%, and 8.3% for days 15, 22, 29, and 36, respectively. Our novel 3D differentiation model can generate functional gametes and is aimed at obviating the need for allogeneic/xenogeneic transplantation. The decreased overall marker expression and the reduced blastocyst development indicated that intrasphere germ cell differentiation correlated with the length of mouse spermatogenesis at approximately 30 days. Future experiments will be conducted to confirm the reproducibility of our findings and the eventual generation of offspring.