Sperm from beta 1,4-galactosyltransferase-null mice are refractory to ZP3-induced acrosome reactions and penetrate the zona pellucida poorly.
Sperm from beta 1,4-galactosyltransferase-null mice are refractory to ZP3-induced acrosome reactions and penetrate the zona pellucida poorly.
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作者：
Q. Lu;B. Shur
多种精子表面成分被认为通过结合卵膜糖蛋白ZP3上的糖苷配体介导配子识别。每种候选受体的功能都基于不同程度的间接和直接证据；然而，这些候选受体的靶向突变对受精的影响尚未报道。在本文中，我们描述了靶向突变对ZP3候选受体beta1,4-半乳糖转移酶的影响，beta1,4-半乳糖转移酶是研究最多的。令人惊讶的是，半乳糖转移酶缺失（gt[-/-]）的雄性是可生育的；然而，与野生型精子相比，gt（-/-）雄性精子结合的放射性标记的ZP3较少，并且不能像野生型精子那样对ZP3或抗半乳糖转移酶抗体进行顶体反应。相比之下，gt（-/-）精子通常会对钙离子载体做出顶体反应，从而绕过ZP3结合的要求。gt（-/-）精子不能经历zp3诱导的顶体反应，这使得它们在生理上不如野生型精子，因为它们在体外相对不能穿透卵皮并使卵母细胞受精。因此，尽管ZP3结合和随后的顶体反应的诱导对于受精是不可缺少的，但它们赋予了受精精子生理上的优势。第二种小鼠的特点是失去了负责zp3依赖性信号转导的长半乳糖基转移酶异构体，但保持了正常的高尔基半乳糖基化水平。来自这些小鼠的精子表明，gt（-/-）小鼠的精卵相互作用缺陷是由于精子表面长半乳糖基转移酶同种异构体的缺失直接导致的，并且与精子发生过程中细胞内半乳糖基化状态无关。
A variety of sperm surface components have been suggested to mediate gamete recognition by binding to glycoside ligands on the egg coat glycoprotein ZP3. The function of each of these candidate receptors is based upon varying degrees of circumstantial and direct evidence; however, the effects on fertilization of targeted mutations in any of these candidate receptors have not yet been reported. In this paper, we describe the effects of targeted mutations in beta1,4-galactosyltransferase, the best studied of the candidate receptors for ZP3. Surprisingly, galactosyltransferase-null (gt[-/-]) males are fertile; however, sperm from gt(-/-) males bind less radiolabeled ZP3 than wild-type sperm, and are unable to undergo the acrosome reaction in response to either ZP3 or anti-galactosyltransferase antibodies, as do wild-type sperm. In contrast, gt(-/-) sperm undergo the acrosome reaction normally in response to calcium ionophore, which bypasses the requirement for ZP3 binding. The inability of gt(-/-) sperm to undergo a ZP3-induced acrosome reaction renders them physiologically inferior to wild-type sperm, as assayed by their relative inability to penetrate the egg coat and fertilize the oocyte in vitro. Thus, although ZP3 binding and subsequent induction of the acrosome reaction are dispensable for fertilization, they impart a physiological advantage to the fertilizing sperm. A second strain of mice was created that is characterized by a loss of of the long galactosyltransferase isoform responsible for ZP3-dependent signal transduction, but which maintains normal levels of Golgi galactosylation. Sperm from these mice show that the defective sperm-egg interactions in gt(-/-) mice are due directly to a loss of the long galactosyltransferase isoform from the sperm surface and are independent of the state of intracellular galactosylation during spermatogenesis.