For growing it is critical to determine the spatial relationship between structures within the embryo. In the early stages of development of the organism is necessary to determine the relative orientation of a plurality of segments and organs of the body.For example, the direction of the head-tail is on the craniocaudal or anteroposterior axis is established very early in embryogenesis (restrainedly axis in the subsequent development), and probably determined by the entry point of the sperm, fertilizing the egg.
The second area dorsoventrally axis, here for definition of dorsal and ventral structures responsible series of interacting proteins and signaling molecules. To install polarity dorsoventral axis along the spinal cord involved of the morphogenetic factor Sonic Hedgehog (discussed later). Finally, it should be installed in the axis that defines left and right side.
This axis is important for proper development of the heart and positioning of internal organs; for example, the anomaly in the X-linked ZIC3 gene involved in the definition of this axis, leads to heart defects and situs inversus, where some organs of the chest and abdomen are on the wrong side.
Three axes presented in the whole embryo, must also be present in the early development of the limb. Within the limb of the organism must determine proximaldistal axis (shoulder-fingers), the anterior-posterior axis (thumb-little finger) and dorsoventral axis (the palm is the back of the hand). At the cellular level individual cells also determine the axis of polarity, for example bezalkoholna axis of the proximal tubular cells or axons, and dendrites of the neuron. Thus, the definition of the axes in the embryo, the limbs and in cells — a fundamental process in development.
Once defined the axis of the body, the body imposes on her development programme. In principle, the formation of axes can be viewed as drawing a line through the mass of cells and determining which end should be head, then the imposition of the program is to divide the embryo into segments and assigning these segments matching, e.g. head, thorax, abdomen and so on.
Gene NOH plays a major role in the determination of the structures along the anteroposterior axis. Ultimately, cells or groups of cells acquire positional information that is associated, primarily, with their position in the body, which determines their further development. (According to the concept of positional information Wolpert, the cell “knows” its location in the coordinate system of the embryo body and differentialsa in accordance with this provision; positional information a cell receives from other cells) human Stem cells derived from early embryos — the subject of intensive research and ethical debate.
Although the use of stem cells for cloning an entire human is extremely unethical and entirely, current research focuses on the creation of specific types of stem cells to correct damaged tissues and organs for regenerative medicine.