Spemann's organizer
The organizer, in the context of embryonic development, refers to a specific region or group of cells within an embryo that plays a pivotal role in regulating and influencing the development of surrounding tissues. The organizer is responsible for releasing signaling molecules that create concentration gradients of these molecules, which in turn guide the differentiation and fate of neighboring cells. This concept was first described by embryologist Hans Spemann, who identified a region in amphibian embryos capable of inducing the formation of neural tissue and other structures.
The organizer is often characterized by its ability to induce changes in neighboring cells that lead to the development of specific tissue types. It sets up instructive signals that direct cells to adopt certain fates and establish different regions within the developing embryo. These signals can include factors that inhibit certain developmental pathways, allowing other pathways to predominate.
The best-known example of an organizer is Spemann's organizer, which was discovered through the Spemann-Mangold experiment. This region, located in the dorsal lip of the blastopore in amphibian embryos, has the ability to induce the formation of neural tissue when transplanted to a different part of the embryo.
In summary, the organizer is a fundamental concept in developmental biology, representing a localized region with the ability to influence and guide the differentiation of neighboring cells during embryonic development. It is central to the establishment of body axes, tissue patterning, and the overall formation of various structures within the developing embryo.
Spemann's organizer is a critical concept in developmental biology that was first proposed and studied by the German embryologist Hans Spemann in the early 20th century. The organizer refers to a specialized region of embryonic tissue that has the remarkable ability to influence the development of nearby cells into specific tissue types and structures. This discovery provided key insights into embryonic development and led to the understanding of cell differentiation and pattern formation.
Experiment:
I. The most famous experiment conducted by Hans Spemann to demonstrate the existence and function of the organizer involved transplantation experiments using salamander embryos. In this experiment, Spemann and his colleague Hilde Mangold performed the following steps:
1. They took an early gastrula-stage embryo of one salamander species.
2. They carefully removed a small piece of tissue from the dorsal lip of the blastopore (the region that would later become the anus).
3. This tissue, now known as the "Spemann-Mangold organizer," was then transplanted into the dorsal lip region of a second embryo from a different salamander species.
4. The transplanted organizer tissue influenced the neighboring cells of the recipient embryo to differentiate into neural tissue, eventually forming a second nervous system.
This experiment demonstrated that the organizer tissue possessed the ability to induce surrounding cells to differentiate into neural tissue, even in a different species. It provided evidence for the existence of signals and molecules involved in pattern formation and tissue differentiation.
II. Grafting Two Embryos Together: In another experiment, Spemann and his student Hilde Proescholdt grafted two embryos together at the gastrula stage, creating a conjoined twin embryo. They grafted the dorsal lip of the blastopore (the organizer) of one embryo onto the ventral side of another embryo. The result was that the grafted tissue induced the host embryo's cells to develop into a secondary nervous system and notochord, essentially creating a Siamese twin with two distinct nervous systems and notochords. This experiment further supported the idea of induction and the importance of the organizer in influencing tissue development.
Both of these experiments provided strong evidence for the role of the organizer in directing embryonic development and inducing neighboring cells to differentiate into specific tissues. They laid the foundation for our understanding of developmental biology and the concept of signaling gradients and interactions that guide the formation of different cell types in a developing embryo.
Types of Organizers:
There are two main types of organizers identified based on their locations and roles during embryonic development:
1. Primary Organizer (or Spemann-Mangold Organizer):
This is the organizer tissue that was originally studied by Hans Spemann and Hilde Mangold. It is formed during gastrulation at the dorsal lip of the blastopore. The primary organizer secretes signaling molecules, such as members of the bone morphogenetic protein (BMP) and Wnt families, that play a crucial role in neural induction and the establishment of the dorsoventral axis.
2. Secondary Organizer:
Also known as axial mesoderm or head organizer, the secondary organizer forms anterior to the primary organizer during the later stages of development. It is responsible for influencing the formation of the head structures in vertebrates. The secondary organizer secretes factors like FGF (fibroblast growth factor) that contribute to the development of the head region.
Spemann's organizer refers to a specialized region of embryonic tissue with the ability to induce neighboring cells to differentiate into specific tissue types. The primary and secondary organizers play crucial roles in pattern formation, neural induction, and the establishment of body axes during embryonic development.