Which of the following statements about compaction is TRUE? The overall size of the embryo grows during compaction Membranes separating individual cells break down Cells on the outside of the compacted embryo become trophoblast After compaction, all cells in the embryo are pluripotent
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" - Compaction is a process that occurs in early embryonic development where the cells (blastomeres) become tightly packed together. This process does not increase the overall size of the embryo; rather, it makes the cells more compact. Therefore, this statement Show more…
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Madhur L.
Mammalian embryos undergo a process known as compaction at the 8-cell stage whereby the loose aggregation of cells "compacts" into a ball with enhanced cell-cell surface contact. You wish to observe this event (compaction), so you flush out newly formed 8-cell embryos from a pregnant mouse and place them in a culture medium that you have prepared. As anticipated, the loose aggregate of cells compacts as you observe them. Your classmate does the same exercise, but does not observe compaction in his embryos. After much discussion, your classmate admits that he did not add Ca++ to his culture medium. Scanning electron micrographs of mouse embryos at the 8-cell stage before compaction and after compaction. The rough appearance of the blastomere surfaces is caused by numerous microvilli. A) If compaction is due to the presence or activation of one type of cell-cell adhesive molecule, what molecule do you think it might be? Explain your choice. B) You then wonder if any additional cell-cell interactions might occur during compaction, so you do the following experiment. You inject two fluorescent dyes individually into one cell of the 8-cell embryo prior to, or after, compaction. You then observe the distribution of the dyes over the next several minutes. One of the dyes is red (designated "R") and has a molecular weight of 40,000 daltons, while the other dye is green (designated "G") and has a molecular weight of 330 daltons. The results of your experiment are shown below. (The letter "G" or "R" in a cell indicates the presence of that dye in the cell.) Is there any evidence of additional cell-cell interactions during compaction? Explain.
Sri K.
Compaction. In mammalian embryos such as the mouse, the fertilized egg divides three times to form eight loosely packed cells, which become tightly adherent in a process known as compaction. In the late 1970 s, several laboratories made antibodies against mouse cell surface proteins. The antibodies prevented compaction, as did removal of $\mathrm{Ca}^{2+}$ from the medium. What sort of protein do the antibodies probably recognize, and why?
Adi S.
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