The timing and mode of hamster blastocyst escape from the zona pellucida in vitro ("hatching") and in vivo were compared on the basis of dynamic and static images captured on videotape and computer, respectively. In vivo, most embryos (> or = 80%) escaped between 0030 h and 0600 h on Day 4 of pregnancy. The zona gradually thinned globally and greatly increased in diameter, eventually disappearing. Attachment of blastocysts to the uterine epithelium followed within 4 h. Retarded embryos also showed global zona lysis. In contrast, zona escape in vitro was delayed > or = 29 h both in blastocysts cultured from 1-cell embryos and in blastocysts flushed from uteri of mated, naturally cycling hamsters at 2330 h on Day 3. Zonae were focally lysed; then blastocysts egressed through the hole, leaving most of the zona intact. Global zona lysis never occurred, and retarded embryos did not escape. In conclusion, the striking morphological and temporal differences in zona escape indicate that the hatching behavior routinely observed in cultured hamster blastocysts is not representative of normal events, and implicate a uterine contribution to normal zona escape that is lacking in culture.

The behaviour of bovine, equine and human blastocysts was studied in vitro by time-lapse videomicrography and computer imaging. This study revealed that cytoplasmic extensions of the trophectoderm ['trophectoderm projections' (TEP)] were expressed by embryos of all three species, prior to or during zona escape. Bovine and human blastocysts escaped their zonae with a combination of blastocoele expansion, collapse and re-expansion coupled with the penetration of the zona pellucida by TEP. In equine embryos, after several cycles of blastocoele expansion and collapse, trophectoderm ruptured the zona with the concomitant appearance of TEP. This study provides documentation that TEP are expressed by a diverse range of mammalian species, bringing the total number of species in which this phenomenon is found to six, since TEP are also known to be expressed by guinea-pig, hamster and rhesus monkey blastocysts, representing rodents, ungulates and primates. In all species studied, the dynamic nature (extension, retraction, and angular movement) of the TEP was similar, moving in an undulating manner with rapid cycles of extension and retraction. Because TEP appear to be a general feature of mammalian blastocysts, they are implicated in one or more key events in early development, namely zona escape, attachment and/or implantation.

No abstract

The authors hypothesized that donor primordial germ cells (PGC) are useful as vehicles of gene transfer in birds. The PGC have been identified in the blastula prior to incubation. They have been isolated from the Stage 7 germinal crescents, Stage 17 blood, and Stage 30 gonads. The percentages of PGC in these three embryonic sources were 2, .003 and 1.5%, respectively. The isolated PGC have been used as antigens to produce specific antibodies that have served as major tools in identification, isolation, and forming enriched in vitro cultures of PGC. Sterile hosts for normal donor PGC have been induced by use of ultraviolet irradiation, treatment with the chemical busulfan, and crossing rooster with female quail to form a sterile host termed "quickens." Micromanipulator technology, along with refinement of techniques to avoid trauma, will allow 80% hatchability. Integration of all the above biotechnology has led to successful use of PGC as vehicles of gene transfer and production of autogenic quail.