Regional specification#Dorsal.2Fventral axis .26 organizer

Spemann's organizer referred to in embryology, the oldest and best-known example of an embryonic signal center. It was discovered by Hans Spemann (1869-1941) and Hilde Mangold ( 1898-1924 ). For his achievements in the field of embryology Spemann was awarded in 1935 the Nobel Prize in Physiology or Medicine. During the development of amphibians, for example, newts and frogs, the pattern formation of an embryo ( ontogeny ) controlled by a particular cell group. This cell group that is " organized " the development of all other cells and was therefore referred to as the organizer of Spemann.

The organizer is located in the so-called "gray crescent " of the fertilized egg. The zygote can be before the first cell division ( cleavage ) are divided into three sections ( see drawing). The dark colored yolk- rich part and the bright yolk- poor part separated by the gray crescent. These areas are distributed on different cells during the segmentation and Blastulation. The cells that emerge from the gray crescent, directly influence the development of the embryo in dorso- ventral direction and cell differentiation in their immediate environment using the emission of different signaling proteins. Chordin this plays a role. This is an inhibitor of TGF -beta- related signaling proteins such as BMP4 (bone morphogenetic protein ). While chordin affects the cells on the dorsal side, BMP acts on the cells to the ventral side. This creates a material gradient ( a gradient ) of the signal activity between the ventral and dorsal, also called " sculpting Gradient". This gradient has shaping function, since by reducing the influence of the BMP -producing cells gastrulation is triggered. It starts namely exactly at the point where the BMP has the lowest concentration, ie directly on the gray crescent. There, the blastopore or primitive mouth is.

Thus, this cluster of cells is crucial for the formation of the longitudinal axis of the embryo through gastrulation because the invagination of the blastopore is connected to a specialization of the tissue in his neighborhood. The role played by the localized to the blastopore lip - cell clusters it has earned him the nickname organizer. The name was linked with that of his co- discoverer Spemann ( Spemann 's organizer ).

Has demonstrated the role of organizer of Hans Spemann and Hilde Mangold by a microsurgical experiment on pig embryos. Transplanting the early gastrula organizer to another embryo to there other location of the target embryo gastrulation begins at two locations. In this way, doubling as a result of two organizer regions, an additional set of body structures, but now on a single embryo. Depending on the site of implantation leading to more or less mature Siamese twins.

Signaling proteins play in other, later formative mechanisms, such as the facial features, a central role. During the manipulation of such mechanisms, for example, created a facial duplication. Mutation of a gene that is responsible for the synthesis of the so-called sonic hedgehog protein, such deformities are also a natural way.