1. Introduction/ Objective 2. Materials 3. Procedure 4. Results 5. Discussion 6. Acknowledgement/ Works Cited/ Links

Effect of ethanol on development of Danio reriro

Brian Hwang
Swarthmore College. Swarthmore, PA
BIO 024, Cebra-Thomas

The objective of the experiment is to determine the effects of ethanol exposure on the embryonic development of zebrafish through observation of physical defomities.

Embryonic development of zebrafish, Danio reriro, is affected by ethanol in a manner similar to higher vertebrates (Blader and Strähle, 1998). Therefore, investigating the effects of ethanol on zebrafish embryo many promote knowledge and understanding of fetal alcohol syndrome in humans. Blader and Strahle confirmed that exposure of zebrafish embryos to ethanol causes cyclopia and craniofacial abnormalities and alters gene expression in the ventral aspects of the fore and midbrain (1998). Exposure of zebrafish embryos to ethanol also induces developmental abnormalities of the notochord and spinal cord, and malformation of the body trunk (Blader and Strähle, 1998).

In order to understand the origin of the deformities, it is necessary to know how embryonic cells of zebrafish normally migrate during gatrulation. During gastrulation, blastoderm cells epibolize over the yolk. When about half the yolk cell becomes covered with blastoderm cells, the margin of epibolizing blastoderm cells form the epiblast and the hypoblast. Epiblast and hypoblast intercalate to form the organizer, known as the embryonic shield, at the dorsal side of the embryo (Gilbert, 2003). Hypoblast cells of the embryonic shield converge, extend anteriorly, and narrow along the dorsal midline of the hypoblast (Gilbert, 2003). Some of these cells eventually form the prechordal plate and the notochord (Gilbert, 2003). Prechodal plate cells seem to be crucial in explaining the origin of ethanol induced deformities.

Though little is known about the underlying mechanisms behind the deformities, it is known that the ectopic position of the prechordal plate cells is characteristic of zebrafish exposed to ethanol (Blader and Strähle, 1998). It is, therefore, believed that ethanol is responsible for the abnormal migration of prechordal plate cells that ultimately causes cyclopia and other deformities. The prechordal plate cells express genes like goosecoid and islet-1, which control cell differentiation in the anterior region of the embryo (Blader and Strähle, 1998). Hence, prechordal-specific genes are expressed ectopically to bring about the observed deformities.

In addition to the deformities, ethanol appears to cause abnormal cell death (Sulik et al., 1988). Ethanol exposure at early development stages results in significant death among the cells destined to give rise to facial structures (Sulik et al., 1988). Ethanol seems to achieve apoptosis by activating the cells’ self-destruction machineries (Sulik et al., 1988). Therefore, in addition to the ectopic prechordal plate-specific gene expression, ethanol induced apoptosis appears to contribute to the observed deformities in zebrafish embryos (Sulik et al., 1988).

This experiment seeks to determine the effects of exposure of ethanol on zebrafish development through observation of physical deformities. Most of the procedures were adopted from Blader and Strähle’s experiment (1998). 30% epiboly stage, also called the late blastula stage, is followed immediately by gastrulation (Gilbert, 2003). Therefore, embryos at 30% epiboly stage at the latest will be used to ensure that ethanol will affect cell migration before it occurs. The results will be compared to Blader and Strahle’s.

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