Stojanov T, O'Neill C
Human Reproduction Unit, Department of Physiology, University of Sydney, Royal North Shore Hospital of Sydney, St. Leonards, New South Wales 2065, Australia.
Biol Reprod. 1999 Mar;60(3):674-82. doi: 10.1095/biolreprod60.3.674.
Platelet-activating factor (PAF; 1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent ether phospholipid. It is one of the preimplantation embryo's autocrine growth/survival factors. It may act via a G protein-linked receptor on the embryo; however, the evidence for this is conflicting. The recent description of the intracellular form of the PAF:acetlyhydrolase enzyme as having structural homology with G proteins and Ras also suggests this as a potential intracellular receptor/transducer for PAF. This study used reverse transcription-polymerase chain reaction to examine the ontogeny of expression of the genes for these proteins in the oocyte and preimplantation-stage embryo. Transcripts for the G protein-linked PAF receptor were detected in the late 2-cell-stage embryo and in all stages from the 4-cell stage to blastocysts. They were also present in unfertilized oocytes and newly fertilized zygotes but only at relatively low levels. The incidence of expression was generally low and variable in late zygotes and early 2-cell embryos. Expression past the 2-cell stage was alpha-amanitin sensitive. The results indicated that mRNA for this receptor is a maternal transcript that was degraded during the zygote-2-cell stage. New expression of the receptor transcript required activation of the zygotic genome. Fertilization of embryos in vitro caused this transcript not to be expressed in the zygote. Culture of zygotes (irrespective of their method of fertilization) caused expression from the zygotic genome to be retarded by more than 24 h. This retardation did not occur if culture commenced at the 2-cell stage. The transcripts for the subunits of intracellular PAF:acetylhydrolase were not detected in oocytes or at any stage of embryo development examined, despite their being readily detected in control tissue. This study confirms the presence of the G protein-linked PAF receptor in the 2-cell embryo and describes for the first time its normal pattern of expression during early development. The adverse effects of in vitro fertilization (IVF) and embryo culture on the expression of this transcript may be a contributing factor for the poor viability of embryos produced in this manner. The reduced expression of PAF-receptor mRNA following IVF predicts that such embryos may have a deficiency in autocrine stimulation and also suggests that supplementation of growth media with exogenous PAF would be only partially beneficial. The effect of IVF and culture may also explain the conflicting literature.
血小板活化因子（PAF；1 - O - 烷基 - 2 - 乙酰 - sn - 甘油 - 3 - 磷酸胆碱）是一种强效醚磷脂。它是植入前胚胎的自分泌生长/存活因子之一。它可能通过胚胎上的G蛋白偶联受体发挥作用；然而，这方面的证据存在矛盾。最近对PAF：乙酰水解酶细胞内形式的描述表明其与G蛋白和Ras具有结构同源性，这也提示它可能是PAF的潜在细胞内受体/转导器。本研究采用逆转录 - 聚合酶链反应来检测这些蛋白的基因在卵母细胞和植入前阶段胚胎中的表达发育情况。在2 - 细胞晚期胚胎以及从4 - 细胞阶段到囊胚的所有阶段均检测到了G蛋白偶联PAF受体的转录本。它们也存在于未受精的卵母细胞和新受精的合子中，但水平相对较低。在晚期合子和早期2 - 细胞胚胎中，表达发生率通常较低且存在差异。2 - 细胞阶段之后的表达对α - 鹅膏蕈碱敏感。结果表明，该受体的mRNA是一种母源转录本，在合子 - 2 - 细胞阶段被降解。受体转录本的新表达需要合子基因组的激活。体外受精的胚胎在合子中导致该转录本不表达。合子培养（无论其受精方式如何）导致合子基因组的表达延迟超过24小时。如果在2 - 细胞阶段开始培养，则不会出现这种延迟。尽管在对照组织中很容易检测到，但在卵母细胞或所检测的胚胎发育的任何阶段均未检测到细胞内PAF：乙酰水解酶亚基的转录本。本研究证实了2 - 细胞胚胎中存在G蛋白偶联PAF受体，并首次描述了其在早期发育过程中的正常表达模式。体外受精（IVF）和胚胎培养对该转录本表达的不利影响可能是导致以此方式产生的胚胎活力不佳的一个因素。IVF后PAF受体mRNA表达降低预示此类胚胎可能存在自分泌刺激缺陷，也表明用外源性PAF补充生长培养基仅具有部分益处。IVF和培养的影响也可能解释了文献中的矛盾之处。
