![]() ![]() Spemann and Mangold found the first evidence of the organizing center, thereafter called the “Spemann organizer”, and its major role in the development of vertebrates. When transplanted to the ventral side of the embryo, the center will induce the formation of a secondary axis, promoting the development of the central nervous system, organs, and tissues, as well as the formation of the main body axis. This center consists of a cluster of cells in the developing embryo that have the ability to interact and instruct morphogenesis in the surrounding cells during gastrulation. Spemann and Mangold discovered the organizing center in the dorsal blastopore lip of amphibians. The major findings were that the transplant had altered the fate of the overlying cells and that the neural folds were built from recipient cells and not donor cells. The transplanted dorsal tissue differentiated mostly into a notochord, while the ectoderm of the host dorsal tissue that was sitting above the transplanted region (blastopore lip) was induced and differentiated to form a Siamese twin containing dorsal tissues such as somites and a neural plate, which would form the central nervous system, forming the bulk of a second axis. In 1924, to understand the processes involved in developmental biology, Spemann and Mangold transplanted a blastopore lip between different ectodermal regions of amphibian embryos. A major milestone had been achieved for developmental biology. This discovery also introduced the concept of induction in embryonic development, which refers to the method used by specific cells to affect the fate of other embryonic cells. ![]() Similar induction events have been shown to be important in the formation of other ectodermal structures, such as the lens of the vertebrate eye (2).In 1924, to understand the processes involved in developmental biology, Spemann and Mangold transplanted a blastopore lip between different ectodermal regions of amphibian embryos. This second neural tube was partially formed from cells in the host embryo that had been instructed, or induced, by the transplanted cells. Not only did a neural tube develop in the normal position, but a second neural tube formed near the transplanted dorsal lip cells. In a series of classic experiments, Mangold and Spemann transplanted cells from the dorsal lip of the blastopore of a donor salamander embryo to a region on the opposite side of a host embryo of a different species of salamander (the two different species were used to allow the donor and host tissues to be distinguished after the transplantation). The ectoderm will form both the epidermis and most of the nervous system, but requires a signal from the cells of the dorsal lip of the blastopore in order to form the neural tube. These three germ layers-the endoderm, mesoderm, and ectoderm-are responsible for forming the various tissues and organs of the embryo. The particular region that Spemann identified, the dorsal lip of the blastopore, is usually referred to as the Spemann organizer in his honor.Įarly in embryogenesis, when the amphibian embryo consists of a ball of cells called the blastula, the formation of an invagination called the blastopore leads to the formation of the three germ layers. This is the idea that certain regions of the embryo, called organizers, are responsible for instructing other tissues to follow particular developmental pathways (1). ![]() One of the most important ideas in developmental biology over the last 75 years was put forth by Hans Spemann based on transplantation in amphibian embryos. ![]()
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