Cross Nicholas L
Department of Physiological Sciences, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Biol Reprod. 2004 Oct;71(4):1367-73. doi: 10.1095/biolreprod.104.030502. Epub 2004 Jun 23.
Ejaculated mammalian sperm must complete a final maturation, termed capacitation, before they can undergo acrosomal exocytosis and fertilize an egg. In human sperm, loss of sperm sterol is an obligatory, early event in capacitation. How sterol loss leads to acrosomal responsiveness is unknown. These experiments tested the hypothesis that loss of sperm sterol affects the organization of cold detergent-resistant membrane microdomains (lipid "rafts"). The GPI-linked protein CD59, the ganglioside GM1, and the protein flotillin-2 were used as markers for lipid rafts. In uncapacitated sperm, 51% of the CD59, 41% of the GM1, and 90% of the flotillin-2 were found in the raft fraction. During capacitation, sperm lost 67% of their 3beta-hydroxysterols, and the percentages of CD59 and GM1 in the raft fraction decreased to 34% and 31%, respectively. The distribution of flotillin-2 did not change. Preventing a net loss of sperm sterol prevented the loss of CD59 and GM1 from the raft fraction. Fluorescence microscopy showed CD59 and GM1 to be distributed over the entire sperm surface. Flotillin-2 was located mainly in the posterior head and midpiece. Patching using bivalent antibodies indicated that little of the GM1 and CD59 was stably associated in the same membrane rafts. Likewise, GM1 and flotillin-2 were not associated in the same membrane rafts. In summary, lipid rafts of heterogeneous composition were identified in human sperm and the two raft components, GM1 and CD59, showed a partial sterol loss-dependent shift to the nonraft domain during capacitation.
射出的哺乳动物精子必须完成一个称为获能的最终成熟过程，才能发生顶体胞吐并使卵子受精。在人类精子中，精子固醇的丢失是获能过程中一个必不可少的早期事件。固醇丢失如何导致顶体反应性尚不清楚。这些实验检验了以下假设：精子固醇的丢失会影响耐冷去污剂膜微区（脂质“筏”）的组织。糖基磷脂酰肌醇连接蛋白CD59、神经节苷脂GM1和蛋白flotillin-2被用作脂质筏的标记物。在未获能的精子中，51%的CD59、41%的GM1和90%的flotillin-2存在于筏组分中。在获能过程中，精子损失了67%的3β-羟基固醇，筏组分中CD59和GM1的百分比分别降至34%和31%。flotillin-2的分布没有变化。阻止精子固醇的净损失可防止筏组分中CD59和GM1的丢失。荧光显微镜显示CD59和GM1分布在整个精子表面。flotillin-2主要位于精子头部后部和中段。使用二价抗体进行贴片显示，很少有GM1和CD59稳定地存在于同一膜筏中。同样，GM1和flotillin-2也不在同一膜筏中。总之，在人类精子中鉴定出了组成各异的脂质筏，并且在获能过程中，两种筏组分GM1和CD59显示出部分依赖于固醇丢失的向非筏结构域的转移。
