The day after the 7th day of the Creation:Breakthrough of human embryo in vitro culture

正Since the creation of intelligent creatures,we are no longer the puppets of the creator.For thousands of years,people have been thinking about the nature and the future of ourselves,and reconstruction of the process of life has become the ultimate dream for us.In 1951,William Harvey,a British scientist,elaborated the theory of the structure and function of embryos for the first time in his book"the reproduction of animals",which established the foundation for people to explore the process and the mechanism of embryonic development.     

Prebursal stem cells in the intraembryonic mesenchyme of the chick embryo at 7 days of incubation.

Cyclophosphamide-treated 18-day-old chick embryos were transplanted with cells from 7-day intraembryonic mesenchyme; the recipients and donors were identical at the major histocompatibility locus. At the age of 35 days, the cell recipients were studied to determine the reconstitution capacity of the transplanted cells. The transplantation resulted in a complete restoration of IgM and IgG class antibody production against human gammaglobulin and Brucella abortus, and of microscopic morphology of the bursa of Fabricius and of the germinal center formation in the spleen. These findings demonstrate that 7-day intraembryonic mesenchyme of the chick embryo harbor prebursal stem cells. These findings confirm our previous observations in the yolk sac-embryo chimeras indicating that lymphoid stem cells originate in the intraembryonic hematopoietic sites.     

Cell proliferation during cicatrization of the integument in the 5 day chick embryo

A cell proliferation study during wound healing of the excised integument of the flank in 5-day chick embryos was performed by pulse labelling using a single isotope (tritiated thymidine). The embryos were operated according to the experimental protocol already published (Thevenet and Sengel, 1973; Thevenet, 1981). 20 microCi of 3H-thymidine were deposited on the integument of the right flank of unoperated (controls) and operated embryos fixed 1 (start control), 2, 12 and 24 h after the excision. Mean labelling index of the unoperated epidermis was 13.7% at 5 days and 21.5% at 6 days of incubation. 2 hours after the excision, labelling index of the operated epidermis increased, on average, to 175% with respect to the labelling index of the controls, in the proximal zones near the wound edges; in the distal zones, the labelling index was lower than that of the controls. The labelling index in the dermis was, on average, 23.4% at 5 days and 28.5% at 6 days of incubation. 2 hours after the excision, the labelling index of the operated dermis increased, on average, to 165% with respect to that of the controls; later it decreased again and remained slightly higher or slightly lower than that of the controls. The increase of the labelling index of the operated integument persisted for a maximum of 6 h after the excision.     

Penetration of chick embryo erythrocytes by toxoplasma gondii tachyzoites in simplified incubation media

The ability of Toxoplasma gondii tachyzoites to penetrate chick embryo erythrocytes (CEE) and the extent of penetration were examined in various simplified, incubation media. Toxoplasma gondii penetrated CEE well in serum-free Eagle's minimum essential medium or in Hanks' balanced salt solution, but much less in phosphate buffered saline (PBS). However, the addition of glucose alone to PBS substantially increased the penetration. A similar effect was seen with other monosaccharides, except galactose. A further, marked increase in penetration was noticed if magnesium ion (but not calcium ion) was added to PBS containing glucose. The present results indicate that T. gondii can penetrate CEE well in simplified incubation solutions such as PBS only when magnesium ion and a monosaccharide are added. Their possible role is discussed in relation to cellular adhesiveness, because the adherence of the parasite to the host cell membrane may be the first step in the penetration process.     

Relative growth rates of maxillary mesenchyme in the chick embryo

Chick embryos were injected with [3H]-thymidine at days 3-7 of incubation and were fixed and embedded in plastic. The embryos were divided into three stage groupings of development [Hamburger and Hamilton: J Morphol 88:49-92, 1951], and labeling indices were determined for each of the following delineated regions within the maxillary process at each stage: region 1, subepithelial mesenchyme located at the medial side of the maxillary process adjacent to the roof of the stomodeum; region 2, subepithelial mesenchyme at the ventral tip of the maxillary process (as seen on cross section); region 3, subepithelial mesenchyme at the lateral portion of the maxillary process below the eye; and region 4, interior mesenchyme defined as the central portion of the maxillary process and separated from the epithelium by the three other regions. Results indicated that differences exist among the regions examined and that these differences were stage specific. At stages 19-21 and stages 24-25 1/2, growth rates were higher in subepithelial regions than interiorly. At stages 28-29, however, a statistically significant difference among the regions was not found. These results suggested that there is an association between growth rates in the maxillary process mesenchyme and its proximity to the overlying epithelium and that these effects are related to the stage of development.