Custom essays on Xenopus and Avian as Model Organisms for Developmental Neurobiology

Avian
Life cycle and nervous system

Avian (chick) is one of the most widely-spread domestic animals available to experiments and widely-used in experiments in different fields of science. The life cycle of the avian includes several key stages through which the bird passes in the course of maturing. The life cycle begins with laying eggs by a chicken. Eggs are the primary stage of the formation of an avian. The embryo inside eggs develops throughout 21 days. During this time, the embryo grows into a chick. The egg must be kept warm for the embryo to survive and to keep the embryo growing. The egg’s shell protects the embryo while it grows. The chick uses its egg tooth to hatch out of the egg. After that the next stage of the life cycle of an avian begins. At first, chicks are wet and have feathers that are called down. The feathers are poorly developed but down dry fast. From the moment of hatching out, chicks can walk right away. They eat seeds, bugs, and worms. Chicks grow more feathers in about four weeks. A comb grows on a chick’s head and a wattle grows under a chick’s beak. Chicks are fully grown into chickens in six months.
The life cycle of avian can be presented as follows:

The nervous system of avians is well-developed and it is more complicated compared to Xenopus. This is why avians are often better and more frequently used by researchers, especially when they conduct researches involving nervous system and neurology.
Benefits of Avian and experiments involving Avian
Today, avians are widely-used in scientific experiments and studies which relate to different fields of science. In actuality, the development of experiments involving avians is determined by the large opportunities to study not only the model after its birth but also avians allow researchers to trace the development of the embryo in an egg, which is very important because it helps researchers to understand better the process of the development of the embryo and changes that occur to the embryo in the course of its formation. At the same time, researchers are interested in the study of avians because they have a lot of similarities to humans. At any rate, in terms of their physiological structure and their nervous system they are closer to humans than Xenopus. As a result, researchers can conduct experiment which can reveal certain reactions and functions of body as well as responses of avians’ body on the impact of external factors to forecast the effects of such influences and functions on humans. Furthermore, experiments involving avians are traditionally reliable and the risk of errors is relatively low. In addition, they do not have limitations at the genetic level such as Xenopus have.
Limitations of Avian and experiments involving Avian
Nevertheless, in spite of seeming usefulness and availability of avains from a scientific point of view, experiments involving avians may have certain limitations. First of all, it is important to understand that avians are not humans. Even though they are widely-used in medical experiments, the outcomes of these studies are not always reliable. In fact, experiments involving avians helped to uncover various diseases and develop effective ways of their prevention. In this respect, it is worth mentioning the avian flu, which have become one of the major threats to the mankind in recent years but researches involving avians helped to tackle this problem. However, researches involving avians and their outcomes cannot be extrapolated on humans to the full extent. In addition, it is important to remember that the nervous system of avians is still different from that of humans that also imposes certain limitations on studies involving avians.
The contribution of Avian made to neuroscience researches
Researches involving avians have a profound impact on the development of the modern science. Numerous studies proved to be particularly helpful in the field of neurology. In this respect, it is possible to refer to the study conducted by A.J. Fischer and others, “Glucagon-Expressing Neurons within the Retina Regulate the Proliferation of Neuron Progenitors in the Circumferential Marginal Zone of the Avian Eye”.
Glucagon-expressing retinal amacrine cells have been implicated in regulating postnatal ocular growth. Furthermore, experimentally accelerated rates of ocular growth increase the number of neurons added to the peripheral edge of the retina. Accordingly, researchers assayed whether glucagon-expressing neurons within the retina regulate the proliferation of progenitors in the circumferential marginal zone (CMZ) of the postnatal chicken eye. Researchers found that glucagon-containing neurites are heavily clustered within the CMZ at the peripheral edge of the retina. Many of these neurites originate from a cell type that is distinct from other types of retinal neurons, which researchers termed large glucagon-expressing neurons (LGENs). The LGENs are immunoreactive for glucagon and glucagon-like peptide 1 (GLP1), have a unipolar morphology, produce an axon that projects into the CMZ, and are found only in ventral regions of the retina. In dorsal regions of the retina, a smaller version of the LGENs densely ramifies neurites in the CMZ. Intraocular injections of glucagon or GLP1 suppressed the proliferation of progenitors in the CMZ, whereas a glucagon-receptor antagonist promoted proliferation. In addition, researchers found that glucagon, GLP1, and glucagon antagonist influenced the number of progenitors in the CMZ. Eventually researchers concluded that the LGENs may convey visual information to the CMZ to control the addition of new cells to the edge of the retina.Wepropose that glucagon/GLP1 released from LGENs acts in opposition to insulin (or insulin-like growth factor) to regulate precisely the proliferation of retinal progenitors in the CMZ.
Xenopus v. Avians
It proves beyond a doubt that both Xenopus and Avians are widely-used in scientific experiments. Both species have their own advantages and drawbacks. In this respect, it should be said that Xenopus can be used successfully in various scientific studies, including genetics, developmental biology, neuroscience and others. However, they have substantial limitations because they are not always applicable when complex experiments have to be conducted because of the relative simplicity of their physiology. In this regard, avians are in an advantageous position because they are more advanced from a physiological point of view. Therefore, more sophisticated experiments may be conducted involving avians. The results of these experiments may be useful for the further studies involving more advanced species and, in some cases, findings of studies involving avians may be useful for humans, especially for the medical science. Consequently, avians are better to use in experiments, although Xenopus are also good models for experiments.

 
Works Cited:
Fischer, A.J. et al. “Glucagon-Expressing Neurons within the Retina Regulate the Proliferation of Neuron Progenitors in the Circumferential Marginal Zone of the Avian Eye.”
Gimlich, R.L. and J.Cooke. “Cell lineage and the induction of second nervous systems in amphibian development.” Nature. 306(5942):471–473.
Kato, Y. et al. “Neuralization of the Xenobus by Inhibition of p/300 Creb-Binding Protein Function.”
Lee, J.E. et al. “Conversion of Xenopus Ecoderm into Neurons by NeuroD, a Basic Helix-Loop-Helix Protein.”
Richter, K., P.J. Good, and I.B. Dawid. “A developmentally regulated, nervous system-specific gene in Xenopus encodes a putative RNA-binding protein.” The New Biologist, 2, 1990, 556-565.
Richter, K., H. Grunz, and I.B. Dawid. “Gene expression in the embryonic nervous system of Xenopus laevis.” Proc. Natl. Acad. Sci. 85 1988, 8086-8090.