The fact that the cells projected in a uniform and consistent way suggests, suggests, the researchers say, that the early blastocyst's axis of bilateral symmetry predicts the spatial patterning of the post-implantation embryo.

"This is the first evidence that the polarity at post-implantation stages, when the body plan is established, can be traced back to events before implantation," says Zernicka-Goetz."

The fact that the fertilized egg of the mouse - and probably other mammals -- share this principle of early organization with other organisms offers fuel for future studies.

"Knowing what we now do, the mouse embryo model will be that much more effective for these studies, and the other models studied may be informative of things we hadn't anticipated; in other words, the finding may make frogs more germane to us," says Zernicka-Goetz.

Researchers have already identified molecular systems in frogs that are strongly implicated in inducing gastrulation, and these systems could play an important role in animals with backbones, including mammals, the researchers say. It is possible that the as-yet-unidentified molecular mechanisms of body formation in the mouse embryo could be similar to those seen in the frog.

The new results, the researchers say, could also prove useful for gaining control over embryonic stem cells. "Looking at what's going on molecularly in embryos at the time of gastrulation could provide insight into the molecular forces underlying embryonic stem cell differentiation," says Pedersen. "This could provide the missing clue as to how to control the differentiation of stem cells in vitro."

The most likely way to get embryonic stem cells to differentiate into specific cell lines, he surmises, is to do what the embryo does - first make them differentiate into endoderm, mesoderm and ectoderm. Once this has been achiev
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Contact: Jennifer O'Brien
jobrien@pubaff.ucsf.edu
415-476-2557
University of California - San Francisco
19-Dec-1999