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Dependence of fertilization in sea urchins, Strongylocentrotus purpuratus, on microfilament formation and internal calcium concentrationBy Megan Lundeberg, Amy Ruggerio and Amy Isaacson

Nominated by Janet Shambaugh, Associate Professor of Biology 

From the Author: As part of an assignment in Developmental Biology, I was asked to examine the reactions of the egg and sperm during the fertilization process of sea urchins. Along with my lab partners, I proposed and conducted experiments to investigate the importance of microfilament formation and calcium concentration to these reactions. I wrote this lab report as a summary of my findings.

From the Faculty Nominator: This report describes original research conducted by Megan and her two lab partners, Amy Isaacson and Amy Ruggerio, in response to an assignment for Bio 378 Developmental Biology. I provided a question and the tools to answer it during an initial laboratory period. The students have one additional week to design and conduct experiments to answer any related question that extends the initial observations. Each student writes an individual report on the findings in the style of a professional journal article with three to five primary sources as references. The intention of this assignment is to have students experience the laboratory as a practicing scientist would. The initial question I pose is deceptively simple to a budding embryologist: Are microfilaments required for the cortical reaction in sea urchin eggs? As the name implies, microfilaments are thin and tiny structures that are used by cells like railroad ties for such processes as muscle movement and cell division and are the targets of some cancer chemotherapy drugs. The cortical reaction refers to a release of substances from the egg surface--substances that create a tough covering around the fertilized egg. This so-called fertilization envelope both prevents further sperm entry and protects the developing embryo. The release is triggered at fertilization by an increase in calcium ions. I provided male and female sea urchins, a microfilament disrupter known as cytochalasin, and a calcium ionophore, which allows calcium to cross cell membranes. The question seems simple to answer—just add cytochalasin into a mixture of eggs and sperm to see if the formation of the fertilization envelope is prevented. If it is prevented, then microfilaments must be required for the cortical reaction. Consider this, however--what if this drug has a toxic effect on sperm? Or is not used at the effective dose? If so, then our conclusions might not be valid. The experimental design must include a plan to test for these and other contingencies. Megan’s report impressed me in several ways. It was evident to me that she and her partners put extraordinary thought into designing their experiments to take into account many contingencies, including those I describe above. In addition, Megan’s report clearly showed that she understood how to write each section as a professional scientist would write. This level of quality is extremely rare for an undergraduate and only comes with practice reading a large number for original research reports in the scientific literature. Megan’s presentation of the results from these experiments was also thorough. In addition, she provided original analysis for her results that showed a depth of understanding. She used more references than required and used them effectively—again, a difficult task for an undergraduate. She must have put extraordinary time into producing this paper that went way beyond my expectations for this assignment. Her efforts with the experiments and the written report demonstrate her true love of science and learning.

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