| Summary: | 碩士 === 國立臺灣大學 === 生化科學研究所 === 89 === The fertilization envelope of fish prevents polyspermy, and protects the embryo from all kinds of environmental damages. At the time of fertilization, eggs undergo cortical reaction, and the chorion is transformed into fertilization envelope (FE). The differences between chorion and FE are that the FE has some new constituents from the cortical granules, and that the constituents of FE are crosslinked. Crosslinking between the molecules of chorion/FE renders FE hardened and robust. At present, it is generally accepted that in fish eggs, transglutaminase (TGase) is responsible for the crosslinking.
In our preliminary study, we confirmed that TGase participates in the hardening of carp chorion. Therefore, we study the property of TGase of carp egg. In carp egg, TGase is located around the cortical granules and on the chorion. It is more abundant in cytoplasm than on chorion. During cortical reaction, the cytosolic TGase is exocytosed and added to the chorion. The molecular weight of TGase of the chorion is 65kDa, and that of cytoplasm is 63kDa. Both have a pI value around 5.9. The TGase activity of egg is totally inhibited by 10mM EDTA or cadaverine. The cytosolic TGase activity is slightly activated in eggs, if compared with oocytes and cortical-reacted eggs whereas the TGase activity on the membrane is not activated. In any stage of egg, the cytosolic TGase activity is higher than that of chorion. Transcription of TGase gene starts very early during oogenesis. Its mRNA can be detected in previtellogenic oocytes. TGase is also expressed in many other tissues, such as liver, kidney, spleen, and brain.
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