Heytens E, Parrington J, Coward K, Young C, Lambrecht S, Yoon S-Y, Fissore R A, Hamer R, Deane C M, Ruas M, Grasa P, Soleimani R, Cuvelier C A, Gerris J, Dhont M, Deforce D, Leybaert L, De Sutter P
Department of Reproductive Medicine, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium.
Hum Reprod. 2009 Oct;24(10):2417-28. doi: 10.1093/humrep/dep207. Epub 2009 Jul 7.
In mammals, oocyte activation at fertilization is thought to be induced by the sperm-specific phospholipase C zeta (PLCzeta). However, it still remains to be conclusively shown that PLCzeta is the endogenous agent of oocyte activation. Some types of human infertility appear to be caused by failure of the sperm to activate and this may be due to specific defects in PLCzeta.
Immunofluorescence studies showed PLCzeta to be localized in the equatorial region of sperm from fertile men, but sperm deficient in oocyte activation exhibited no specific signal in this same region. Immunoblot analysis revealed reduced amounts of PLCzeta in sperm from infertile men, and in some cases, the presence of an abnormally low molecular weight form of PLCzeta. In one non-globozoospermic case, DNA analysis identified a point mutation in the PLCzeta gene that leads to a significant amino acid change in the catalytic region of the protein. Structural modelling suggested that this defect may have important effects upon the structure and function of the PLCzeta protein. cRNA corresponding to mutant PLCzeta failed to induce calcium oscillations when microinjected into mouse oocytes. Injection of infertile human sperm into mouse oocytes failed to activate the oocyte or trigger calcium oscillations. Injection of such infertile sperm followed by two calcium pulses, induced by assisted oocyte activation, activated the oocytes without inducing the typical pattern of calcium oscillations.
Our findings illustrate the importance of PLCzeta during fertilization and suggest that mutant forms of PLCzeta may underlie certain types of human male infertility.
在哺乳动物中，受精时卵母细胞的激活被认为是由精子特异性磷脂酶Cζ（PLCζ）诱导的。然而，PLCζ是否为卵母细胞激活的内源性因子仍有待确凿证实。某些类型的人类不育症似乎是由精子无法激活卵母细胞所致，这可能是由于PLCζ存在特定缺陷。
免疫荧光研究表明，PLCζ定位于可育男性精子的赤道区域，但缺乏卵母细胞激活能力的精子在同一区域未显示出特异性信号。免疫印迹分析显示，不育男性精子中的PLCζ含量降低，在某些情况下，还存在分子量异常低的PLCζ形式。在一例非圆头精子症病例中，DNA分析鉴定出PLCζ基因中的一个点突变，该突变导致该蛋白催化区域出现显著的氨基酸变化。结构建模表明，这种缺陷可能对PLCζ蛋白的结构和功能产生重要影响。将与突变型PLCζ对应的cRNA显微注射到小鼠卵母细胞中时，未能诱导钙振荡。将不育的人类精子注射到小鼠卵母细胞中未能激活卵母细胞或触发钙振荡。注射此类不育精子后，通过辅助卵母细胞激活诱导两个钙脉冲，可激活卵母细胞，但不会诱导典型的钙振荡模式。
我们的研究结果说明了PLCζ在受精过程中的重要性，并表明PLCζ的突变形式可能是某些类型人类男性不育症的潜在原因。
