Xenopus Laevis Lab Report

During the first lab experience involving Xenopus laevis, I had many questions. One of my most burgeoning questions was the result of the in vitro fertilization of the Xenopus eggs. To begin, the female frogs were gently massaged in a manner that was similar to the method of amplexus males use in order to release the eggs. The released eggs were placed in a petri dish where they were to be fertilized by the sperm of a male frog, who had donated his life prior to the running of the IVF treatment. In order to fertilize the eggs, the testis was diced into a small piece and then was moved around the petri dish touching every egg present in hopes of fertilizing each one. The eggs were then left for five minutes before adding a simple saline solution.
During this process, my main questions revolved around the egg. Before making contact with the testis and the eggs had a greenish-white and black appearance. The somewhat resembled marbles covered in goop. As the sperm and egg made contact the eggs appeared to become more distinct in color. Within each fertilized egg there was a white half and a darker grey-black half. These halves I learned were the vegetal (white) and animal (gray-black). The vegetal half was nearly always on the bottom of the fertilized eggs as it is denser than the newly rapidly dividing animal half.
From the Jones and Lopez textbook, I was able to initially learn that egg activation is a “series of biochemical and physical changes in the egg” (pg 166-167). Egg activation includes the cortical reaction, completion of meiosis, an increase in the metabolic rate of the egg, as well as the synthesis of proteins, RNA, and DNA. Each of these steps is fundamental to preparations required for embryonic development. If the initial release of Ca++ during egg activation takes place, the developing zygote will be able to continue