Ultrastructure, protein synthesis and secretion of day-6 rabbit blastocysts cultured in a chemically defined, protein-free medium

Promotion of gastrulation by maternal growth factor in cultured rabbit blastocysts

Rabbit blastocysts of day 6 post coitus were cultured in a chemically defined, protein-free medium for 24 h. Although the trophoblast continued to grow, the embryonic disc degenerated. Addition of basic fibroblast growth factor (FGF-2, of human recombinant or bovine origin, 10 ng/ml) to the culture medium resulted in significant developmental progress. The embryonic disc became pear-shaped showing a round anterior edge and a posterior node. The primitive streak and Hensen's node indicated that gastrulation had begun. Mesoderm formation was confirmed from histological sections and by localization of the expression of T-gene transcripts in whole-mount preparations. FGF-2 mRNA was detected in both day-6 endometrium and day 6-blastocysts using in vitro translation followed by immunoprecipitation with a monoclonal antibody to FGF-2. In the uterine secretions of day-6 pregnant and pseudopregnant animals, several proteins exhibiting FGF-2 antigenicity were detected on Western blots following two-dimensional gel electrophoresis. As day-6 blastocysts required exogenous FGF-2 in vitro and as FGF-2 of uterine origin is present in the uterine secretion, the maternal growth factor can promote gastrulation in vivo.

Effect of oxygen concentration in the incubator's gas phase on the development of cultured preimplantation rabbit embryos

Development of rabbit preimplantation embryos cultured under 20, 5 or 1% oxygen was studied. Three-day-old morulae were cultured in a protein-free medium (BSM II supplemented with 5 mg PVP/ml medium) for 24 and 48 h. Embryonic development was evaluated by gross morphology and by incorporation of tritiated thymidine as an indicator of cell proliferation. The lower oxygen concentrations yielded significantly better embryo development at 24 and at 48 h than the 20% concentration. There was no significant difference in development between 5% and 1% oxygen. Addition of the radical scavanger superoxiddismutase (SOD), either alone or in combination with catalase or reduced glutathione, did not improve embryo development even in the 20% oxygen group. Our data suggest the need to reduce in vitro oxygen levels from 20% to more physiological concentrations.

Effect of various growth-promoting factors on preimplantation bovine embryo development in vitro

One-cell bovine embryos produced by in vitro oocyte maturation (IVM) and in vitro fertilization (IVF) were cultured in chemically defined medium (CDM) to which the following growth-promoting factors were added separately: transferrin (Tf, 10 ug/ml), epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), transforming growth factor-betal (TGF-beta1), insulin-like growth factor-one (IGF-I), insulin-like growth factor-two (IGF-II), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and nerve growth factor (NGF), all at 10 ng/ml. The embryos were cultured for a total of 10 days and were assessed. The culture medium was changed every 2 days. There were no beneficial effects of growth factors on embryo development to morula or hatched blastocyst stages of development. However, supplementation with EGF approached significance (P<0.08) when compared with that of CDM alone at the blastocyst stage of development. The results suggest that supplementation with growth factors does not improve bovine IVM-IVF embryo development when cultured under chemically-defined conditions.

Fibroblast growth factor induces primitive streak formation in rabbit pre-implantation embryos in vitro

Culturing of rabbit pre-implantation embryos was performed in Ham's F10 medium supplemented with polyvinylpyrrolidone. Under these culture conditions, day 6 post coitum blastocysts increased their diameter within 24 h to 80% of that of day 7 blastocysts grown in vivo. Despite this substained growth, the embryonic disc remained undifferentiated with clear signs of degeneration after 24 h of culture. Basic fibroblast growth factor (bFGF) was able to overcome this developmental block. After 12 h of culture, day 6 blastocysts showed pear-shaped embryonic discs, and after 24 h, the primitive streak with Hensen's node was visible. The bFGF had no comparable effects on day 5 and day 7 blastocysts. The embryonic discs of day 5 blastocysts degenerated, even in the presence of bFGF, whereas day 7 blastocysts were able to form their primitive streak, also in the absence of bFGF. TGF beta 1 did not promote embryonic development in vitro. The data indicate that the onset of mesoderm formation in the rabbit is controlled by a growth factor of the FGF-family.