Download letters to the editor - AJP - Regulatory, Integrative and Comparative

Am J Physiol Regulatory Integrative Comp Physiol 283: R549–R551, 2002;
10.1152/ajpregu.00107.2002.
letters to the editor
The following letters refer to an “In focus” article by
H. Ehmke (Developmental physiology of the cardiovascular system. Am J Physiol Regulatory Integrative
Comp Physiol 282: R331–R333, 2002).
The Chicken Embryo in Developmental Physiology of
the Cardiovascular System: A Traditional Model with
New Possibilities
http://www.ajpregu.org
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0363-6119/02 $5.00 Copyright © 2002 the American Physiological Society
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To the Editor: In the February 2002 issue of American
Journal of Physiology-Regulatory, Integrative and
Comparative Physiology, Ehmke (7) focuses on unsolved issues and interesting findings in the field of
developmental physiology of the cardiovascular system. Ehmke addresses the need for new useful models
to study embryonic/fetal cardiovascular structure and
function and rightly points out the potential of the
zebrafish (Danio rerio) as an experimental model. The
merits of this model organism for integrative physiology were reviewed by Briggs (4).
The chicken (Gallus gallus) is a species that deserves
attention when the developmental physiology of the
cardiovascular system is considered. The attractiveness of the chicken embryo as an experimental model
to study angiogenesis (1), heart formation (11, 20), and
the development of neurohumoral cardiac control (12,
19) has long been recognized. Recent studies have
shown that the chicken embryo, like the zebrafish (9),
can also be used to study developmental changes in
local vascular tone and hemodynamic control. Reactivity of isolated femoral and carotid arteries of chicken
embryos can be studied by means of wire myograph
techniques from embryonic day 15 of the 21 days of
incubation (15), and precise surgical preparation and
intravital microscopy enable the measurement of mesenteric vascular diameter in the intact fetus at even
earlier stages of development (22). Very recently the
changes in pulmonary arterial reactivity during the
transition from in ovo to ex ovo life (which takes more
time than in mammalians and therefore can be studied
in more detail) have been investigated in the chicken
embryo (25).
Other studies have used fluorescent microspheres
and cannulation procedures (branches of chorioallantoic vein) to investigate time-dependent changes in
cardiac output distribution, blood pressure, and heart
rate in early and late stages of incubation (2, 3, 18, 26).
These studies have provided methods that give important insights in the development of cardiovascular
physiological mechanisms in the chicken embryo. In
addition, they demonstrate substantial comparability
in basic mechanisms of fetal cardiovascular control
between the chicken and mammalian species (6). The
response to acute hypoxia has been extensively studied
in this respect (6, 10, 17).
As Ehmke (7) mentions and argues is the case for the
zebrafish (4), a good experimental model should also
give the opportunity to study the developmental function of single genes or complex genetic pathways. The
role of specific genes and transcription factors, like
endothelial PAS protein 1, in cardiovascular development has been investigated in the chicken embryo (8).
A “chicken alternative” for the endothelin (ET)-1 and
ET type A receptor null mice has even been made by
pharmacological in ovo inactivation of the gene product
(14). Over the past few years, worldwide collaborations
have made large progress in the production of a molecular map of the chicken genome and provide new molecular tools (e.g., microarray) (24). This and the large
diversity in genotypes (due to natural and experimental selection) that are also phenotypically characterized (for instance, see Refs. 16, 21) will only increase
the potential of the chicken embryo to be used as a
model to unravel the role of specific genes in developmental physiology.
As the chicken embryo, like the zebrafish, develops
outside the mother, effects of external stresses on cardiovascular development can be studied without interferences of maternal hormonal, metabolic, or hemodynamic alterations. The most common causes of
prenatal stress, namely malnutrition and chronic hypoxia (as seen in placental insufficiency), can be studied
independently (13, 23, 27), and pharmacological or
toxic substances are easily applicable via injections of
compounds into the air cell (5). These practical advantages make the chicken embryo and the adult chicken,
in which cardiovascular pathology has been observed
(16, 21), important animal models to study mechanisms in the intriguing new field of developmental
physiology that deals with the prenatal programming
of cardiovascular pathology. This tractability for experimental manipulation, its rich history in developmental biology, the short incubation time, and the new
possibilities of genomic tools emphasize the importance of the chicken embryo as a model organism in
developmental physiology of the cardiovascular system
alongside traditional models, such as the fetal sheep,
and promising new models, like the zebrafish.
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Villamor E, Ruijtenbeek K, Pulgar V, De Mey JGR, and
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chicken embryos during transition to ex vivo life. Am J Physiol
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K. Ruijtenbeek
Dept. of Pediatrics
University Hospital Maastricht
6202 AZ Maastrict, The Netherlands
J. G. R. De Mey
Dept. of Pharmacology & Toxicology
Cardiovascular Research Institute Maastricht
6200 MD Maastricht, The Netherlands
E-mail: [email protected]
C. E. Blanco
Dept. of Pediatrics
University Hospital Maastricht
6202 AZ Maastrict, The Netherlands
REPLY
To the Editor: I thank Ruijtenbeek et al. for their
comments. They rightly make the point for the chicken
embryo as a model system to study cardiovascular
integrative physiology and homeostasis during development. The chicken embryo shares several features
with the zebrafish, like an external development, a
relatively short incubation time, and a wide availability, which substantially facilitate its investigation.
Furthermore, later stages of embryological development are very similar in the chicken and mouse embryo, and many fundamental mechanisms of development (e.g., those of limb formation) have been
discovered in this species. Indeed, the major textbook
Principles of Development by Wolpert and colleagues
(16) lists the chicken embryo, together with Xenopus
laevis, Drosophila melanogaster, Caenorhabditis elegans, Arabidopsis thaliana, the mouse, and the zebrafish, as one of the canonical model systems of developmental biology.
Nevertheless, the virtues of the chicken embryo and
the zebrafish as model systems of developmental physiology should not be confused. For many reasons, the
zebrafish will remain the dream system for genomewide screens (2, 6, 12). Its short generation time and
large progeny size, high permeability to molecules
added to the water, external development, and trans-
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8.
LETTERS TO THE EDITOR
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LETTERS TO THE EDITOR
REFERENCES
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1. Altimiras J and Crossley DA II. Control of blood pressure
mediated by baroreflex changes of heart rate in the chicken
embryo (Gallus gallus). Am J Physiol Regulatory Integrative
Comp Physiol 278: R980–R986, 2000.
2. Briggs JP. The zebrafish: a new model organism for integrative
physiology. Am J Physiol Regulatory Integrative Comp Physiol
282: R3–R9, 2002.
3. Crossley D II and Altimiras J. Ontogeny of cholinergic and
adrenergic cardiovascular regulation in the domestic chicken
(Gallus gallus). Am J Physiol Regulatory Integrative Comp
Physiol 279: R1091–R1098, 2000.
4. Dragon S and Baumann R. Erythroid carbonic anhydrase and
hsp70 expression in chick embryonic development: role of cAMP
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AJP-Regulatory Integrative Comp Physiol • VOL
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Villamor E, Ruijtenbeek K, Pulgar V, De Mey JGR, and
Blanco CE. Vascular reactivity in intrapulmonary arteries of
chicken embryos during transition to ex ovo life. Am J Physiol
Regulatory Integrative Comp Physiol 282: R917–R927, 2002.
Wolpert L, Beddington R, Jessell T, Lawrence P, Meyerowitz E, and Smith J. Principles of Development (2nd ed).
Oxford: Oxford Univ. Press, 2001.
Heimo Ehmke
Institut für Physiologie
Universität Hamburg
20246 Hamburg, Germany
E-mail: [email protected]
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parency mean that zebrafish are ideally suited for
large-scale random mutagenesis screens. Over the past
20 years, a huge amount of genomic information has
been accumulated, and it is expected that the entire
zebrafish genome will become available in the near
future. Because the gene order appears to be conserved
in most parts of zebrafish and human chromosomes,
genetic screens in zebrafish will most likely help us to
understand the function of human genes.
However, the cardiovascular system of the chicken
resembles the human cardiovascular system much
more closely than does that of the zebrafish. As emphasized by Ruijtenbeek et al., the basic mechanisms of
cardiovascular control seem to be very similar in
chicken and mammalian species (1), and cardiovascular physiology and pathology can be well studied in
adult chicken. In addition, much physiological information is available for the chicken. This is also reflected by a surge of recent studies on chicken embryos
published in American Journal of Physiology-Regulatory, Integrative and Comparative Physiology (1, 3–5,
7–11, 13–15). Thus the chicken appears to be particularly suited for studies investigating the long-term
consequences of factors acting during embryogenesis.