1. Mike Meade
Dr. Srinivasan
Developmental Biology
26 April 2015
The Development of Cardiogenic Mesoderm
Introduction
As already known, the three germ layers that develop during gastrulation
eventually develop into necessary structures for the body through the process of
organogenesis including vital organs such as the heart. What is to be explained in this
review is the specification and development of cardiac mesoderm, also known as the
heart field. The heart field is divided in the primary and secondary heart field. The
secondary heart field forms at the anterior portion of the body and the right ventricle and
cardiac outflow tract are eventually derivatives of it (Brand 2003). There are many
signaling paths and proteins that are involved in the formation of cardiac mesoderm
including BMP, noggin/chordin, wnt, mesp1, and mmp-3. Specifically there will be a
focus on BMP and noggin in this review as well as their interactions with all of the
aforementioned proteins and pathways.
The Importance of Inhibition
Before going any further it may useful to mention and briefly explain inhibition
since it is one of the most important aspects of development in regard to cardiac
mesoderm that first must be understood is the interaction of proteins and pathways in

2. their regard to turn others on or inhibit others. A very crucial example of this is the
ability of noggin and chordin to inhibit BMP, specifically BMP-4. By noggin and chording
inhibiting BMP the cardiac and blood-forming fields will not form in the center of an
embryo. Another inhibitory effect is the effect of dickkopf to repress wnt. An over
expression of wnt without inhibition leads to an overabundance of cells marked for blood
rather than cardiac mesoderm. Of course these paths of inhibition are not so simple
requiring cascading of signals and will be explained further later in the review.
Cardiogenic Mesoderm Develops from Lateral Plate Mesoderm
Cardiogenic mesoderm specifically develops from lateral plate mesoderm
through various signaling. While noggin and BMP are both important in developing
cardiogenic mesoderm, Wnt is also necessary and must be inhibited in order for later
signals of BMP to perform their job. BMP activates two genes known as Nkx2-35 and
Mesp1. Mesp1 is important for multiple reasons including that it prevents heart
progenitors from being re-specified as another type of mesoderm and also represses
brachyury, sox17, and goosecoid insuring that cardiac precursor cells will not become
other structures such notochord or endoderm (Gilbert p.453). In relation to Wnt, Mesp1
activates the dickkopf gene, which is a Wnt inhibitor. Wnt must be inhibited in order for
BMP to properly perform its function and signaling path.
PARM1 enhances BMP signaling
At this point it is obvious to see that BMP signaling is important in the
specification of cardiogenic mesoderm, but there also has to be signaling that regulates
BMP signaling. An article from 2012 showed the effects off the protein PARM1 on BMP

3. signaling. At normal levels PARM1 may not have as much of an effect on BMP, but
over expression enhances the effects of BMP2 and BMP4 (Nakanishi, N., Takahashi,
T., Ogata, T., Adachi, A., Imoto-Tsubakimoto, H., Ueyama, T., & Matsubara, H. 2012).
The expression of PARM1 is followed by mesodermal markers, which happens during
the differentiation of cardiomyocytes. Cardiomyocytes develop from cardiac mesoderm,
so the larger picture in BMP signaling and PARM1 is through the specification and
development of cardiac mesoderm to eventually develop fully into cardiomyocytes or
cardiac muscle cells.
Noggin Increases the Expression of MMP-3
As previously stated, noggin is an inhibitor of BMP and also critical during
development of cardiac mesoderm and cardiomyocytes. In addition to interacting with
BMP, noggin also interacts with mmp-3 by increasing the expression of it. Without
noggin present BMP is an inhibitor of mmp-3. If mmp-3 is inhibited by BMP there is a
decrease in cardiac differentiation. Mmp-3 is necessary for the activation of genes such
as Gata-4 which are specific cardiac markers that allow for cells to differentiation and be
specified for cardiac development (Hong, S., Kang, J., Park, J., Ryu, E., Choi, S., Lee,
S., . . . Seo, J. 2010). In the development of cardiac mesoderm and cardiomyocytes it
is often important to not only understand how certain proteins and genes are turned on
and what they contribute to the cascading of signals, but also to understand why some
are turned off. In this part of development it is necessary for BMP to be inhibited by
noggin. If it were the case that noggin was not inhibiting BMP, then mmp-3 would not
be able to activate Gata-4 and other cardiac markers. Without the activation of Gata-4,

4. differentiating cells would not be able to be marked for creating cardiac mesoderm and
then developing into cardiomyocytes.
BMP Activates MESP1
As noted earlier, wnt signaling must be inhibited by genes such as dickkopf and
Cerberus in order for BMP to convert lateral plate mesoderm to cardiac mesoderm. If
BMP is not present in order to activated mesp1, which activates dickkopf, then wnt
would not be inhibited. Wnt, specifically wnt8 actually inhibits the formation of cardiac
mesoderm, but instead is important in specifying cells to the fate of blood. While blood
is clearly a very important and necessary part of the body of nearly all living beings, if
wnt is never inhibited then there can be no heart formation because the formation of
cardiac mesoderm and cardiomyocytes may be interrupted and possibly not form all
due to over expression of cells marked for the fate of blood. This is another case in
which is critical to see how inhibition of certain signaling paths is required for other
structures to form. Over expression of wnt8 without ever being inhibited would convert
all lateral plate mesoderm to become specified for blood and cardiac mesoderm would
not be able to properly develop.
Current Model of Cardiogenic Mesoderm Development
The current model of the development of cardiogenic mesoderm is tied in with all
of the aforementioned signaling pathways as well as later plate mesoderm. Wnt, BMP,
noggin, Mesp1, and others are all crucial. The neural tube secretes wnt signals that
specify lateral plate mesoderm to hemangiogenic mesoderm (blood). In the anterior
part of the body, dickkopf inhibits wnt, which allows BMP and FGF8 to work on

5. converting lateral plate mesoderm to cardiogenic mesoderm. Also to be noted here is
that FGF and BMP are both needed in the posterior for heart formation (Brand 2003)
Chordin and noggin are secreted from the notochord so that blood-forming fields are not
formed in the middle of the embryo. Chordin and noggin of course are inhibitors of BMP
and block BMP signaling. BMP activates Mesp1, which in turn activates dickkopf.
Mesp1 when activated also prevents genes that would specify cells for fates other than
cardiac mesoderm. This is the basic model of the development and specification of
cells for cardiac mesoderm. To go further into the development of cardiomyocytes is to
further understand BMP signaling and its inhibition by noggin. BMP must be inhibited
by noggin in order for mmp-3 to activate cardiac markers such as gata-4, which mark
differentiating cells for the creation and development of cardiomyocytes.
The Problems With the Current Model
The current model of the specification of cardiogenic mesoderm and the
development of cardiomyocytes is still not perfect and an area of current research. One
thing that is unclear is how noggin can elevate mmp-3 expression (Hong, S., Kang, J.,
Park, J., Ryu, E., Choi, S., Lee, S., . . . Seo, J. 2010). In the experiment entitled
“Association of Matrix metalloproteinase-3 with cardiogenic activity during Noggin-
induced differentiation of mouse embryonic stem cells” from 2010 the researchers
explored how inducing noggin affects mmp-3. They were able to show that mmp-3 is
regulated and has increased activity due to noggin, but were unable to tell exactly how
noggin was doing this. Also it seems unclear if BMP is alone required to activate mesp1
and if another signaling path could achieve the same thing. This is important because it
leads to the inhibition of wnt8. This leads to another gap in the model. If nothing is

6. there to inhibit wnt, then can cardiac mesoderm even attempt to develop or do all cells
become specified for hemangiogenic mesoderm? It is crucial to understand all of these
aspects of development in order to understand if each signaling pathway is sufficient for
their role and if their over expression (in other words not being inhibited when
necessary) causes serious issue in development.
Possible Future Research and Experiments
Certain experiments would be necessary in order to fill the gaps in the current
models for the development of cardiac mesoderm and cardiomyocytes. An experiment
to attempt to solve the gap of how noggin elevates mmp-3 could be to see how BMP
acts on mmp-3 in the absence of noggin. In other word perform a “lose it” experiment
losing noggin. Also it would be necessary to ensure that BMP was close enough to act
on mmp-3. Next is the question of whether the absence of BMP would cause over
expression of wnt where it is normally inhibited and if cardiac mesoderm in those areas
(posterior) would be able to form. This could be another “lose it” experiment in which
BMP was removed from the posterior. If cardiac mesoderm was still able to form in the
posterior half, then wnt8 may not be capable of inhibiting it on its own or another
signaling pathway may be able to activate mesp1, which would in turn activate dickkopf
to block wnt signaling. If cardiac mesoderm was not able to develop and there was an
overabundance of cells being specified for hemangiogenic mesoderm then the opposite
would be true.

7. Annotated Bibliography
1. Nakanishi, N., Takahashi, T., Ogata, T., Adachi, A., Imoto-Tsubakimoto, H.,
Ueyama, T., & Matsubara, H. (2012). PARM-1 promotes cardiomyogenic
differentiation through regulating the BMP/Smad signaling pathway. Biochemical
and Biophysical Research Communications,428(4), 500-505.
2. Hong, S., Kang, J., Park, J., Ryu, E., Choi, S., Lee, S., . . . Seo, J. (2010).
Association of Matrix metalloproteinase-3 with cardiogenic activity during Noggin-
induced differentiation of mouse embryonic stem cells. International Journal of
Cardiology, 141(1), 49-60.
3. Kattman, S., Witty, A., Gagliardi, M., Dubois, N., Niapour, M., Hotta, A., . . .
Keller, G. (2011). Stage-Specific Optimization of Activin/Nodal and BMP
Signaling Promotes Cardiac Differentiation of Mouse and Human
Pluripotent Stem Cell Lines. Cell Stem Cell, 8(2), 228-240.
4. Liu, Y., Asakura, M., Inoue, H., Nakamura, T., Sano, M., Niu, Z., . . . Schneider,
M. (2007). Sox17 is essential for the specification of cardiac mesoderm in
embryonic stem cells. PNAS,104(10), 3859–3864-3859–3864.
5. Schneider, V., & Mercola, M. (2001). Wnt antagonism initiates cardiogenesis in
Xenopus laevis. Genes and Development, 15(1), 304-315.
6. Brand, T. (2003). Heart development: Molecular insights
into cardiac specification and earlymorphogenesis. Developmental
Biology, 258(1), 1-19.

8. 7. Gilbert, S. (2014). Lateral Plate Mesoderm and the Endoderm.
In Developmental Biology(10thed., Vol. 1, pp. 451-453). Sunderland, MA:
Sinauer Associates.
Figures/Examples
Figure 1: Example of BMP being antagonized (inhibited) in blastula stage. While this is
not during gastrulation as discussed in the review it allows for the ability to see how
BMP is inhibited and its expression patterns.

9. Figure 2: Development pathway to cardiac mesoderm showing BMP gradients
Figure 3: Lateral Plate Mesoderm to Cardiac Mesoderm Specification