Mitchell L A, Nixon B, Aitken R J
Reproductive Science Group, Discipline of Biological Sciences, School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW, Australia.
Mol Hum Reprod. 2007 Sep;13(9):605-13. doi: 10.1093/molehr/gam043. Epub 2007 Jun 26.
Mammalian spermatozoa must undergo a post-ejaculatory period of maturation, known as capacitation, before they can engage in the process of fertilization. Studies in the mouse have established that capacitation facilitates sperm-zona recognition via mechanisms that involve the appearance of tyrosine phosphorylated chaperone proteins on the sperm surface overlying the acrosome, the site of sperm-zona recognition. In this study, we examined whether a similar relationship existed between the tyrosine phosphorylation events associated with capacitation and sperm-zona interaction in human spermatozoa. These studies confirmed that capacitation is associated with an increase in both sperm-zona binding and an increase in tyrosine phosphorylation over the sperm tail. However, we could not detect the surface expression of phosphotyrosine residues over the sperm head, as observed with murine spermatozoa. Moreover, although we could clearly detect a number of chaperone proteins in human spermatozoa including HSPE1, DNAJB1, HSPD1, HSPA1A, HSPCA, HSPH1, HSPA5 and TRA1, none of these molecules were expressed on the sperm surface. On the basis of these results, it is unlikely that these proteins play an active role in the remodeling of the sperm surface during capacitation. We conclude that strong species-specific differences exist in the molecular mechanisms that drive sperm-egg recognition and that alternative, chaperone-independent, mechanisms must underpin sperm-zona interaction in the human.
哺乳动物的精子在射精后必须经历一段成熟过程，即获能，之后才能参与受精过程。对小鼠的研究表明，获能通过一些机制促进精子与透明带的识别，这些机制涉及顶体（精子与透明带识别的部位）上方精子表面酪氨酸磷酸化伴侣蛋白的出现。在本研究中，我们检测了与获能相关的酪氨酸磷酸化事件和人类精子与透明带相互作用之间是否存在类似关系。这些研究证实，获能与精子与透明带结合增加以及精子尾部酪氨酸磷酸化增加有关。然而，我们无法检测到精子头部磷酸酪氨酸残基的表面表达，而在小鼠精子中可以观察到这种表达。此外，尽管我们能够清楚地检测到人类精子中的多种伴侣蛋白，包括HSPE1、DNAJB1、HSPD1、HSPA1A、HSPCA、HSPH1、HSPA5和TRA1，但这些分子均未在精子表面表达。基于这些结果，这些蛋白质在获能过程中对精子表面重塑发挥积极作用的可能性不大。我们得出结论，在驱动精卵识别的分子机制中存在强烈的物种特异性差异，并且在人类中，精子与透明带相互作用必定有其他不依赖伴侣蛋白的机制作为支撑。
