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Spemann-Mangold Organizer
[1]
By: Philbrick, Samuel O'Neil, Erica Keywords: Organizers [2] Induction [3] Amphibians [4]
The Spemann-Mangold organizer [6], also known as the Spemann organizer [6], is a cluster of
cells in the developing embryo of an amphibian that induces development of the central
nervous system [7]. Hilde Mangold [8] was a PhD candidate who conducted the organizer [6]
experiment in 1921 under the direction of her graduate advisor, Hans Spemann [9] at the
University of Freiburg [10] in Freiburg, Germany. The discovery of the Spemann-Mangold
organizer [6] introduced the concept of induction [11] in embryonic development. Now integral to
the field of developmental biology, induction [11] is the process by which the identity of certain
cells influences the developmental fate of surrounding cells. Spemann received the Nobel
Prize in Medicine in 1935 for his work in describing the process of induction [11] in amphibians
[12]. The Spemann-Mangold organizer [6] drew the attention of embryologists, and it spurred
numerous experiments on the nature of induction [11] in many types of developing embryos.
In the first three decades of the twentieth century, Hans Spemann [9] experimented and led
graduate students in conducting experiments with South African clawed frog [13] embryos (
Xenopus laevis [14]) and newt embryos (Triturus taeniatus and Triturus cristatus [15]). Spemann
also developed the microtools needed for early experimental embryology [16], namely glass
needles [17] and micropipettes. To make a glass needle, Spemann held a glass rod over a
burner and pulled it apart so that it became incredibly thin in the middle. The thin needle-like
part of the rod was broken off, and then placed over a smaller burner called a micro-burner,
another one of Spemann?s inventions. When heated and drawn a second time, the needle
had an even finer point that allowed experimental embryologists to take embryos out of the
jelly membranes in which they were ensconced. Additionally, Spemann created micropipettes
that relied on the suction created by a piece of rubber covering the top of the hollow, thin
glass rod. The rubber could be depressed by the thumb of the user to create a minute amount
of suction and was useful for transplantation experiments. Experimental embryologists used
micropipettes to remove cells from developing gastrulas, and transplant the cells to new sites.
Prior to the Spemann-Mangold organizer [6] experiment, Spemann had focused on constricting
salamander [18] eggs at the blastopore [19] lip by tying single strands of his baby son?s hair
around the tiny eggs. Spemann observed that when the hair tightly constricted the eggs at the
dorsal end, across the blastopore [19] lip, two embryos developed. Spemann also tested the
degree to which constricting the embryo with hair led to different levels of conjoinment. For
example, when Spemann constricted the eggs only a little, two heads formed, but if he pulled
the hair strand tighter, the embryos developed separate heads and sets of forelimbs.
However, when Spemann conducted the same experiment but separated the dorsal end from
the ventral end by constriction, only the dorsal end developed, while the other half was left in
a vegetative state.
Building on those initial experiments, Spemann investigated how cell fates were determined
during embryogenesis [20]. Spemann was particularly interested in exploring the mechanism of
neural plate [21] induction [11]. The neural plate [21] is the embryonic structure that gives rise to
the central nervous system [7] during development. To explore neural plate [21] induction [11],
Spemann first performed a transplant experiment that was nearly identical to the later
organizer [6] experiment. Spemann transplanted the blastopore [19] lip from one newt gastrula [22]
into another, and noticed a second notochord [23] that developed at the site of transplantation.
However, the newts were of the same species and it was difficult to determine whether the
host tissue or transplanted tissue was acting to create the second nervous system.
Based on the intra-species transplantation experiments, Spemann hypothesized that the cells
at the blastopore [19] lip were composed of ectoderm [24]. The rationale was that the
transplanted cells appeared to assimilate with the ectoderm [24] of the host?s cells to form
neural structures. Spemann also believed the cells at the blastopore [19] lip became
determined in their fate first, and that fixed determination [25] then spread outward from that
blastopore [19] lip across the ectoderm [24]. Spemann was mistaken, however, as the organizer
[6] experiment would later demonstrate. Cells at the blastopore [19] lip are not ectoderm [24], but
mesoderm [26]. The mesoderm [26] cells of the blatopore lip invaginate over the course of
gastrulation [27] and are subjacent to the ectoderm [24].
Spemann revised his previous hypothesis after conducting transplantation experiments
between different newt species of the same genus. The eggs from one newt species were
pigmented (Triturus taeniatus), while eggs from the second species of newt were
unpigmented (Triturus cristatus [15]), allowing for visual identification of which tissues gave rise
to features observed. The transplantation of ectoderm [24] cells from one species (Triturus
cristatus [15]) at a distance from the blastopore [19] of a second newt?s gastrula [22] (Triturus
taeniatus) revealed that the transplanted tissue was progressively pulled towards the
blastopore [19] lip. Spemann realized that the cells at the lip of the blastopore [19] were
invaginating inward. Thus the ectoderm [24] undergoing neural differentiation [28] would be
sitting atop mesoderm [26] that formerly comprised the blastopore [19] lip. The blastopore [19] lip
was therefore composed of pre-mesodoermal cells that initiated the invagination of
surrounding cells in a process called gastrulation [27], which gives rise to the three embryonic
germ layers [29] (ectoderm [24], mesoderm [26], and endoderm [30]).
In the spring of 1921, Spemann assigned his graduate student, Mangold, with the task of
conducting a cross-species transplant of blastopore [19] lips between different newt species.
The tissue color was different between species, allowing Mangold to see whether the features
that developed were from transplanted or host tissue. Mangold used the microtools developed
by Spemann to excise the blastopore [19] lip of the unpigmented Triturus cristatus [15] egg [31],
and transplant it under the ectoderm [24] of a pigmented Triturus taeniatus newt egg [31]. The
transplanted blastopore [19] lip differentiated into a notochord [23] and somites [32], while the
ectoderm [24] of the host tissue that was sitting above the transplanted mesoderm [26]
differentiated into a neural plate [21]. The neural plate [21] then went on to form neural arches
and a completely separate central nervous system [7]. The ultimate result was what appeared
to be two embryos conjoined at the gut.
The importance of the organizer [6] experiment is the discovery that a part of the mesoderm [26]
influences the ectoderm [24] as the ectoderm [24] differentiates into central nervous system [7]
tissue. Spemann and Mangold published their finding of the amphibious organizer [6] in 1924
in the article, ?Über Induktion von Embryonalanlagen durch Implantation artfremder
Organisatoren (Induction of Embryonic Primordia by Implantation of Organizers from a
Different Species)?.
The techniques used to discover the Spemann-Mangold organizer [6] had limitations. The
technique for transplanting the organizer [6] involved surgery at a cellular scale, and it
demanded great precision. When possible, transplanting was difficult, and many things could
not be transferred under the surface of the ectodermic layer because it is only one cell thick in
many places. The fact that many materials could not be transplanted kept scientists from
testing the inductive capacity of other cellular materials on the embryo. The Einsteck method
circumvented that limitation. Spemann and Otto Mangold [33], Hilde Mangold?s husband,
developed the technique. While each claimed credit for the novel technique, the exact origin
of its invention is unknown. Spemann proposed that both may have discussed the idea
conversationally, and that each investigator felt justified in claiming credit for the idea.
The Einsteck method consists of using the glass and hair microsurgical tools developed by
Spemann to plant material inside of the blastocoels of a developing embryo in either the
blastula [34] or early gastrula [22] stage. This technique insures that material need not fuse with
or adhere to the ectodermic layer. It simply passes through the ectoderm [24] into the cavity
beneath, where it can affect the embryo. The insertion wound also heals quickly, leaving the
foreign material within the developing embryo to affect change.
Spemann?s co-researcher, Hanns Bruno Geinitz [35] transplanted a Spemann-Mangold
organizer [6] into developing blastocoels using the Einsteck method, which induced embryos
like the ones obtained in Spemann and Mangold?s original experiments. Geinitz expanded on
the original organizer [6] experiment by transferring organizers from frogs and toads into
salamander [18] gastrulae. Geinitz called this type of transfer xenoplastic because it involved
transplant of cells from a different genus, as opposed to heteroplastic, which involved crossspecies transfers like those used by Spemann and Mangold.
Although it was initially proposed that the Spemann-Mangold organizer [6] induced
differentiation [28] of the central nervous system [7], more recent mechanistic examinations have
revealed more complicated genetic interactions. Embryologists have determined that the
presence of the Spemann-Mangold organizer [6] impedes signaling to the overlying ectoderm
[24]. Instead of becoming skin cells, the organizer [6]-affected ectoderm [24] cells become central
nervous system [7] tissue. In 1992, Richard M. Harland [36] and William C. Smith [37] at the
University of California at Berkeley [38] in Berkeley, California discovered a protein integral to
cellular induction [11] at the Spemann-Mangold Organizer [5]. As the protein was essential for
neural development [39] and eventually the formation of the head, the scientists called it noggin
[40].
Since that discovery, the collective work of many experimental embryologists has revealed
patterns of genetic interactions. The developing blastula [34] secretes bone morphogenetic
protein-4 (BMP-4) from the ventral side of the embryo, opposite the organizer [6]. BMP-4
diffuses throughout the blastocoel [41] and induces skin cells where it binds to ectodermal cells.
However, the organizer [6] blocks BMP-4 from binding to the surrounding ectoderm [24] by
secreting the proteins chordin [42] and noggin [40]. Chordin and noggin [40] bind to BMP-4 in the
organizer [6]-affected area to prevent BMP-4 from binding to ectoderm [24] receptors. Instead of
becoming skin cells, the ectodermal cells in the area of the organizer [6] take the default path
of becoming central nervous system [7] tissues.
Edward De Robertis [43], the first scientist to isolate the Homeobox gene in 1984 and the codiscoverer of the protein chordin [42] in 1994, published a review of the changing conception [44]
of the organizer [6], ?Spemann?s Organizer and Self-Regulation in Amphibian Embryos.? In
the review, De Robertis covers much of the recent research examining the role of RNA and
gene signaling in embryonic induction [45]. De Robertis also explains the tendency of
embryonic cells to differentiate into neural plate [21] cells when exposed to organizing material
observed in many experiments that followed Spemann?s original publications.
The amphibious Spemann-Mangold organizer [6] has developmental analogues in both fish [46]
(embryonic shield) and bird (Hensen?s node) embryos that are responsible for body plan
arrangement. Spemann and Mangold?s work with induction [11] and organization [47] in
developing amphibian embryos culminated in Spemann being awarded the Nobel Prize in
Medicine in 1935. The Nobel Prize is not posthumously awarded, and Mangold had died prior
to Spemann's award. Embryologists continue to study the Spemann-Mangold organizer [6] and
induction [11] as they relate to body plans and nervous system development in amphibians [12].
Sources
1. Amundson, Ron. The Changing Role of the Embryo in Evolutionary Thought.
Cambridge: Cambridge University [48] Press, 2005.
2. Balinsky, Boris Ivan. An Introduction to Embryology [49]. Philadelphia: W. B. Saunders,
1970.
3. De Robertis, Edward M. ?Spemann?s Organizer and Self-Regulation in Amphibian
Embryos,? Nature Reviews Molecular Cell Biology 7 (2006): 296?302.
4. Fulton, Chandler, and Attila O. Klein. Explorations in Developmental Biology [50].
Cambridge: Harvard University Press [51], 1976.
5. Hamburger, Viktor. The Heritage of Experimental Embryology [52], Hans Spemann [9]
and the Organizer. New York: Oxford University Press, 1988.
6. Holtfreter, Johannes. ?Neural Induction in Explants which have Passed through a
Sublethal Cytolysis.? In Explorations in Developmental Biology [50], ed. Chandler Fulton
and Attila O. Klein. Cambridge: Harvard University Press [51], 1976. Abridged and
originally published in Journal of Experimental Zoology [53] 106 (1947): 197?222.
7. Kimball, John W. ?Organizing the Embryo: The Central Nervous System,? Biology
Pages, last modified May 17, 2011.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Spemann.html [54] (Accessed
November 28, 2011).
8. Maienschein, Jane. Whose View of Life? Cambridge, MA: Harvard University Press [51],
2003.
9. Sasai, Yoshiki, Bin Lu, Herbert Steinbeisser, Douglas Geissert, Linda K. Gont, Edward
M. De Robertis. ?Xenopus Chordin: A Novel Dorsalizing Factor Activated by OrganizerSpecific Homeobox Genes,? Cell 79 (1994): 779?90.
10. ?Spemann, Hans.? In Hutchinson Dictionary of Scientific Biography, ed. Roy Porter,
566?69. Oxford: Helicon Publishing, 2005.
11. Smith, William C., and Richard M. Harland [36]. ?Expression Cloning of Noggin, a New
Dorsalizing Factor Localized to the Spemann Organizer in Xenopus Embryos.? Cell 70
(1992): 829?40.
12. Spemann, Hans, and Hilde Mangold [8]. ?Induction of Embryonic Primordia by
Implantation of Organizers from a Different Species,? The International Journal of
Developmental Biology [50] 45 (2001): 13?38. Originally published in Archiv für
Mikroskopische Anatomie und Entwicklungsmechanik [55], 100 (1924): 599?63.
13. Waddington, Conrad Hal, Joseph Needham [56], and Dorothy M. Needham. ?PhysicoChemical Experiments on the Amphibian Organizer.? In Explorations in Developmental
Biology [50], ed. Chandler Fulton and Attila O. Klein. Cambridge: Harvard University Press
[51], 1976. Originally published in Nature 132 (1933): 239.
14. Zimmerman, Lyle B., Jose M. De Jesus-Escobar, and Richard M. Harland [36]. ?The
Spemann Organizer Signal Noggin Binds and Inactivates Bone Morphogenetic Protein4.? Cell 86 (1996): 599?606.
The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells
in the developing embryo of an amphibian that induces development of the central nervous
system. Hilde Mangold was a PhD candidate who conducted the organizer experiment in
1921 under the direction of her graduate advisor, Hans Spemann, at the University of Freiburg
in Freiburg, German. The discovery of the Spemann-Mangold organizer introduced the
concept of induction in embryonic development. Now integral to the field of developmental
biology, induction is the process by which the identity of certain cells influences the
developmental fate of surrounding cells. Spemann received the Nobel Prize in Medicine in
1935 for his work in describing the process of induction in amphibians. The SpemannMangold organizer drew the attention of embryologists, and it spurred numerous experiments
on the nature of induction in many types of developing embryos.
Subject
Embryos [57] Amphibians [58] Spemann, Hans, 1869-1941 [59] Embryological development [60]
Gastrulation [61] Developmental biology [62] Embryology, Experimental [63] Cell differentiation [64]
Nobel Prize winners [65] Neural tube [66] Somatic embryogenesis [67] Organizers, Embryonic [68]
Embryonic Induction [69]
Topic
Processes [70]
Publisher
Arizona State University. School of Life Sciences. Center for Biology and Society. Embryo
Project Encyclopedia.
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