Final answer:
Axis formation in the mouse embryo is determined by signals from extra-embryonic tissues, particularly involving the node and primitive streak, which play a crucial role in establishing the body's three-dimensional structure through signaling.
Step-by-step explanation:
The formation of axes in the mouse embryo is a critical aspect of its development. After fertilization, during the process known as gastrulation, complex interactions occur involving signals from the embryo's environment that lead to differentiation and the establishment of the body axes. Extra-embryonic tissues, particularly the primitive streak and the node, play a crucial role in signaling to the internal cells of the embryo about how to organize into the body's three-dimensional structure. These structures release chemical signals that guide the formation of the anterior-posterior axis, amongst others.
Furthermore, experiments, like the one by Spemann and Mangold, confirmed that certain cells are genetically programmed to define the body's axis by transplanting dorsal cells and observing the development of a second notochord in the transplanted site of the embryo. This signifies that axis formation is under strong genetic control and the influence of specific localized cell groups. Therefore, the correct answer to the question, 'How is axis formation in the mouse embryo determined?' is E. By signals from extra-embryonic tissues, as this option encompasses the role of significant structures such as the node, which is part of the extra-embryonic tissues.