Kim Kye-Seong, Gerton George L
Pochon CHA University College of Medicine, Cell and Gene Therapy Research Institute, CHA General Hospital, Seoul, Korea.
Dev Biol. 2003 Dec 1;264(1):141-52. doi: 10.1016/j.ydbio.2003.08.006.
Although its exact role in fertilization is unknown, the acrosome is a very important, exocytotic organelle overlying the anterior aspect of sperm from many species. Structurally and functionally, the acrosome can be considered to consist of soluble and particulate compartments. One component of the particulate acrosomal matrix is the zona pellucida-binding protein sp56. Our demonstration that this protein is within the acrosomal matrix and not on the sperm plasma membrane has led us to reexamine the events of acrosomal exocytosis and the role of the sperm acrosomal matrix in the fertilization process. To visualize the soluble compartment, we have utilized sperm from transgenic mice that carry soluble green fluorescent protein (GFP) in their acrosomes and, as a means to assess the exposure of acrosomal matrix components, we have tested the ability of these sperm to bind beads coated with antibodies to sp56. The loss of GFP from the acrosomes and the binding of the beads by the sperm undergoing capacitation serve as indicators of distinct stages of acrosomal exocytosis, allowing us to define intermediates of acrosomal exocytosis that occur during the course of sperm capacitation. These experiments demonstrate that the exposure and release of acrosomal proteins during spontaneous acrosomal exocytosis is not synchronous but is regulated during capacitation. Furthermore, acrosomal exocytosis under these conditions required calcium in the medium. On the basis of these findings, we propose an alternative model for acrosomal exocytosis that considers a role for these intermediates of exocytosis during capacitation and sperm-ZP interactions.
尽管顶体在受精过程中的确切作用尚不清楚，但它是覆盖许多物种精子前端的一个非常重要的、进行胞吐作用的细胞器。从结构和功能上看，顶体可被认为由可溶性和颗粒性区室组成。颗粒性顶体基质的一个成分是透明带结合蛋白sp56。我们证明这种蛋白存在于顶体基质内而非精子质膜上，这使我们重新审视顶体胞吐作用的过程以及精子顶体基质在受精过程中的作用。为了观察可溶性区室，我们利用了在顶体中携带可溶性绿色荧光蛋白（GFP）的转基因小鼠的精子，并且，作为评估顶体基质成分暴露情况的一种方法，我们测试了这些精子结合包被有抗sp56抗体珠子的能力。顶体中GFP的丢失以及获能精子对珠子的结合，作为顶体胞吐作用不同阶段的指标，使我们能够定义在精子获能过程中发生的顶体胞吐作用的中间阶段。这些实验表明，在自发顶体胞吐作用过程中顶体蛋白的暴露和释放并非同步，而是在获能过程中受到调控。此外，在这些条件下顶体胞吐作用需要培养基中的钙。基于这些发现，我们提出了一种顶体胞吐作用的替代模型，该模型考虑了这些胞吐作用中间阶段在获能和精子与透明带相互作用过程中的作用。
