Rat hepatoma reuber H-35 cells produce a 2-cell stage-specific inhibitor of the cleavage of mouse embryos.

We purified an embryonic stage-specific inhibitor produced by rat hepatoma Reuber H-35 cells against cleaving mouse 2-cell embryos and defined its biological properties. Zygotes obtained from CD-1 mice (a strain that shows a 2-cell block in vitro) or C57BL/6 and B6C3F1 mice (strains that do not) were cultured in media with and without 50 microM EDTA, respectively. The development of the zygotes from all strains was arrested at the 2-cell stage when zygotes were cocultured with Reuber H-35 cells. However, the embryos from C57BL/6 and B6C3F1 were less sensitive than those from CD-1 against the inhibitory effects of development. This inhibitory effect was also evident in medium conditioned with the Reuber H-35 cells. The factor from the conditioned medium was separated into its < 10 000 M(r) fraction by ultrafiltration and was further purified in fraction B-25 as a single peak by reverse-phase column chromatography. An incubation as short as 3-h during the late 2-cell stage (G2 phase) with fraction B-25 suppressed cleavage in 61.5% of the CD-1 embryos (30.3% in control culture). Although the inhibitory effect was reversible, embryos that cleaved again either degenerated or were retarded at various stages in their subsequent development. Additionally, a long-term incubation of developing zygotes with the inhibitory factor caused a significant reduction in [3H]thymidine (TdR) incorporation into the DNA of CD-1 2-cell embryos as well as developmental arrest at the interphase of the 2-cell stage. These results indicated that this factor will serve as a valuable tool with which to clarify the proliferating mechanism of the preimplantation embryo.