Lipid is an important constituent of cell membrane. Membrane lipid composition of spermatozoa has been correlated to different function. Many researchers have related membrane lipid with survival success after cryopreservation or cold shock. Sperm maturation and acrosome reactions are natural phenomenon, but cryopreservation or cold shock is not. Therefore, sperm cells are not programmed for such change and undergo stress. So the change in membrane lipid composition due to cold shock or cryopreservation may be looked upon as response of spermatozoa to a certain stressed condition. A significant body of research worked on the relationship between membrane lipid and fatty acid composition and ability of cell to tolerate adverse change in temperature. However, as the approach of different research groups was different, it is very difficult to compare the changes. Studies have been done with different species, ejaculated/seminal or epididymal sperm. Lipid analyses have been done with whole cell membrane isolated by different methods. Fatty acids estimated were from whole cell, plasma membrane, head membrane, or phospholipids. The cryopreservation condition, media composition, and diluents/cryoprotectants were also different. At this onset a comprehensive review is needed to cover changes of sperm membrane lipid composition of different species under different cryopreservation conditions. 1. Introduction Sperm cell is unique in many respects including structure and function. It is capable of fertilizing egg; it functions in a body different from its origin and gender. Its plasma membrane is also different from most other cell membranes in lipid composition. It contains high amount of polyunsaturated fatty acids (PUFA), especially diPUFA (phospholipids esterified with two PUFA), which is found only in sperm, retina, and certain brain areas [1, 2]. In particular, PUFA are known to contribute to membrane fluidity and flexibility [3–5]. Membrane lipid composition has been related to their specific functions, because it promotes the creation of microdomains with different fluidity, fusogenicity, and permeability characteristics [2], required for reaching and fusing with the oocyte. Phospholipids are the most representative lipid fraction of the sperm cell membranes, of which phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin are the major components [6]. Lipid and fatty acid composition of sperm cells differ not only for different animals [7, 8] but also for different species [9–12], even for fertile and subfertile population of same species
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