精子成熟和体外受精

无论在体内或体外,精子和卵子的成熟对于受精的成功都是必需的。精子的成熟不仅包括在雄性动物体内所发生的过程,亦包括在雌性动物所发生的获能过程。牛精子是在输卵管中获能。在体内,获能活性存在于发情时的输卵管液中,而不存在于黄化输卵管液中。实验证明,发情输卵管液的获能活性是因其中含有氨基多糖(Glycosaminoglycan):肝素或硫酸肝素。在体外,肝素可使牛精子获能,使鲜精或冻精的受精率超过70％。用肝素获能的精子作体外受精,已能使胚胎发育,并已出生犊牛。肝素使精子获能的机理尚不清楚。肝素可     

哺乳动物精子获能机理及体外研究

精子获能是哺乳动物精卵融合之前必须经历的一个阶段。自发现精子获能现象以来,对精子获能机制的研究已取得一些进展,但仍有不少问题需要进一步研究。精子获能为体外受精研究获得突破性进展,为人类直接观察受精过程和研究受精机理奠定了基础。文章主要对精子获能的变化、机制及体外研究进行了综述。     

添加物对精子体外获能的影响及其分子机制

获能是哺乳动物精子的成熟过程和受精的必要前提,获能液中添加物从不同方面影响精子获能;本文阐述了肝素、Ca2 载体A23187、葡萄糖、孕酮、咖啡因等添加物对精子体外获能的影响及其作用机制。     

水貂银狐精子体外获能前后表面元素变化的研究

哺乳动物精子的体外获能是体外受精中的一个关键问题,而元素成分又在精子获能中发挥着极其重要的作用。Yanagimachi(1982)提出仓鼠精子的体外获能与钙元素有关;Mrsny等(1987)发现钾、镁元素是仓鼠精子获能和顶体反应所必需的;Hyne(1984)又证实钠也是豚鼠精子体外获能或顶体反应最重要的元素。然而,在野生动物水貂和银狐精子获能前后元素成分的变化,至今国内外尚     

精液中去获能因子的研究进展

精子与卵母细胞融合形成新生命是高度契合的复杂事件,获能反应的发生对该进程具有关键性的作用。精子为完成获能反应,会释放稳定质膜状态的因子,这些因子被定义为去获能因子,过早释放或者异常释放去获能因子,将引起精子的质膜不稳定提前获能,最终影响精子进入雌性生殖道的运动能力。目前,对去获能因子的研究,主要集中在分离鉴定及功能探究,并取得一定的进展。本文对近年来探究的去获能因子按照作用机理进行了分类,归纳总结了功能特征等方面的信息,为改善精子获能条件和提高精卵结合发生率奠定分子生物学基础,对解释获能现象及精卵结合机制提供更深层次的科研思路。     

不同培养液对蓝狐精子体外获能效果的比较试验

采用上游法分离优化精子,用mTyrod’s液(T)、BO液(B)以及高渗液(HIS)3种不同培养液,在5%CO2的培养箱中进行获能培养,获能培养时间为6h。利用考马斯亮蓝染色法检测精子顶体反应率,伊红-苯胺黑染色法检测活精子比率以及观测法检测精子活力。在培养的0、1、2、4、6h时分别检测上述指标并统计分析,从而筛选出适合蓝狐精子体外获能的培养液。结果显示:B培养液优于T、HIS培养液,最佳获能培养时间t≥6h;HIS可以提高精子顶体反应率,但较高的渗透压不利于精子保存,不建议使用。     

苯甲酸钠咖啡因对牛精子体外获能的影响——牛精子穿入去透明带仓鼠卵实验

K·Goto 等用含咖啡因的 BO 液(Brac-ketl 和 Oliphant,1975)对牛精子进行体外获能处理,成功地完成了体外受精。部分受精牛卵发育至桑椹期。我们用苯甲酸钠咖啡因(上海兽药厂产)作试剂,添加到 BO 溶,液中,对牛精子进行体外获能培养,发现牛精子很快死亡。为此,我们研究了该种试剂对牛精子体外获能的影响及提高苯甲酸钠咖啡因对牛精子体外获能促进作用的方法。     

哺乳动物精子获能的分子机制

精子获能是精子能够与卵母细胞发生顶体反应和受精的一个重要生理前提。精子获能的分子机制相当复杂,许多报道表明精子获能受到多种细胞信号途径的调控。尽管目前尚未完全明确,但是许多研究表明获能精子发生许多结构和生化变化,包括蛋白酪氨酸磷酸化、精子膜胆固醇外流、活性氧的产生及精子膜超极化,这些变化都有助于精子获能的发生。Ca2 和HCO3-通过对cAMP的调控有助于获能完成,葡萄糖、孕酮和肝素作为获能液的重要添加物,通过不同途径促发精子获能。文章从这些方面对获能做一综述,在此基础上提出以后的研究方向。     

获能液及精子密度对牛性控精子体外受精成功率的影响

本实验探讨了不同的精子获能添加物、精子密度、精子获能液对牛性别分离精子体外受精（IVF）的影响。结果表明：受精液中同时添加10μg/mL的肝素与5mmol／L的咖啡因,能促进牛性控精子体外获能与受精。精子密度在1．0×10^6个/mL时其囊胚发育率最高。用BO液和mTyrode’s液对牛性控精子进行获能和受精处理．其受精效果差异不显著（P〉0．05）,但BO液作用时间短对早期胚胎的发育影响较小,比较适合牛性控精子IVF。     

葡萄糖在牛体外受精及胚胎发育中的影响

在牛精子获能液中添加不同浓度的葡萄糖,应用体外培养技术对牛精子体外获能及早期胚胎发育进行研究,通过观察顶体反应、超激活、活率和早期胚胎发育率,筛选出获能液中最适葡萄糖浓度及其有利于牛早期胚胎发育的最佳浓度.结果表明:葡萄糖是精子获能和维持超激活运动的主要能源物质,其代谢过程中产生的活性氧在牛精子体外获能、受精过程中起重要作用,高浓度(超过9.15 mM)葡萄糖有利于获能的完成;但是对早期胚胎发育不利,对早期胚胎发育来说其最适添加量为6.10 mM,此时的囊胚率最高.     

Effect of capacitation of stallion sperm with polyvinylalcohol or bovine serum albumin on penetration of bovine zona-free or partially zona-removed equine oocytes

Experiments were conducted to study effects of macromolecules on stallion sperm capacitation and fertilization as determined by penetration of bovine zona-free and equine partially zona-removed oocytes. Stallion sperm were capacitated in TYH medium (modified Krebs-Ringer bicarbonate) supplemented with either 1 mg/mL of polyvinylalcohol (PVA) or 4 mg/mL of BSA. Capacitation was induced with 8 bromoadenosine cyclic monophosphate (8BrcAMP; 0.5 mM) alone or in combination with 0.1 microM of ionomycin. Intraspecies gametes were co-incubated in TYH/PVA or TYH/BSA for 18 to 20 h. For zona-free bovine oocytes, penetration rate (35%) with the combination of 8BrcAMP and ionomycin in PVA-containing medium was higher (P < 0.05) than any treatment in BSA-containing medium (5 to 6%). A similar study was conducted using equine oocytes with partially removed zonae. Sperm capacitated and used for in vitro fertilization (IVF) in PVA-containing medium had higher penetration rates (P < 0.01) than sperm in BSA-containing medium (54 vs. 11%). The effect of equine preovulatory follicular fluid on bovine oocyte penetration was assessed. Bovine oocytes were matured in tissue culture medium-199 with 0, 20, 50, or 100% equine preovulatory follicular fluid, and 1 IU/mL of equine chorionic gonadotropin. Stallion sperm were treated with 8BrcAMP + ionomycin in PVA- or BSA-containing media. The penetration rates of bovine zona-free oocytes by stallion sperm were again higher with PVA (47%) than BSA (18%; P < 0.01). Penetration rates of oocytes matured in 100% follicular fluid were higher (P < 0.05) than for oocytes matured with 0% follicular fluid. The effects of equine follicular fluid and PVA/BSA during sperm capacitation on standard bovine IVF were examined. Culture of bovine oocytes with equine follicular fluid did not affect oocyte maturation or penetration rates after IVF. Bovine sperm capacitated with heparin in PVA-containing medium yielded lower (P < 0.05) fertilization rates than those capacitated in BSA-containing medium when incubated with both zona-intact and zona-free bovine oocytes. In summary, PVA was superior to BSA for ionophore-induced capacitation of equine sperm for penetration of zona-free bovine oocytes or partially zona-removed equine oocytes, but not for standard bovine IVF with bovine sperm. Zona-free bovine oocytes may be useful for assaying in vitro capacitation and fertilization of stallion sperm.     

Methyl‐β‐Cyclodextrin Improves Sperm Capacitation Status Assessed by Flow Cytometry Analysis and Zona Pellucida‐Binding Ability of Frozen/Thawed Bovine Spermatozoa

Mammalian sperm undergo a series of biochemical transformations in the female reproductive tract that are collectively known as capacitation. Cyclodextrins added to the sperm culture medium have been described to induce in vitro sperm capacitation, enabling its use in protein‐free media. However, the additive capacitating effect of methyl‐β‐cyclodextrin (MβCD) in the medium containing bovine serum albumin (BSA) is unknown in the bovine species. In this study, we evaluated the effects of incubating frozen–thawed bovine spermatozoa in a BSA‐containing medium supplemented with MβCD on different sperm quality and functional parameters. Sperm viability decreased with the addition of MβCD in a dose‐dependent manner (p < 0.05), and DNA damage could be observed but only with the highest concentration of MβCD. However, pre‐incubation of spermatozoa in MβCD‐supplemented medium improved the capacitation status as assessed by the increase in plasma membrane fluidity, intracellular calcium concentration, induced acrosome reactivity and zona pellucida (ZP)‐binding ability (p < 0.05). Thus, we conclude that MβCD supplementation is able to enhance the capacitation status of frozen–thawed bovine spermatozoa cultured in capacitation medium containing BSA and could result in a valid strategy for its application on artificial reproductive technologies such as in vitro fertilization or intracytoplasmic sperm injection.     

牛成熟卵母细胞体外受精的研究进展

这篇论文论述了牛成熟卵母细胞体外受精的研究进展,主要从精子的制备方法,获能液的组成、精子获能的判定、受精方,法以及卵母细胞受精与否的评定5个方面加以阐述,并展望了体外受精的研究方向。     

Effects of exposure to methylglyoxal on sperm motility and embryonic development after fertilization in mice

Methylglyoxal (MG) is a precursor for the generation of endogenous advanced glycation end-products involved in various diseases, including infertility. The present study evaluated the motility and developmental competence after in vitro fertilization of mouse sperm which were exposed to MG in the capacitation medium for 1.5 h. Sperm motility was analyzed using an SQA-V automated sperm quality analyzer. Intracellular reactive oxygen species (ROS), membrane integrity, mitochondrial membrane potential, and DNA damage were assessed using flow cytometry. The matured oocytes were inseminated with MG-exposed sperm, and subsequently, the fertilization and embryonic development in vitro were evaluated in vitro. The exposure of sperm to MG did not considerably affect the swim-up of sperm but resulted in a deteriorated sperm motility in a concentration-dependent manner, which was associated with a decreased mitochondrial activity. However, these effects was not accompanied by obvious ROS accumulation or DNA damage. Furthermore, MG diminished the fertilization rate and developmental competence, even after normal fertilization. Collectively, a short-term exposure to MG during sperm capacitation had a critical impact on sperm motility and subsequent embryonic development after fertilization. Considering that sperm would remain in vivo for up to 3 days until fertilization, our findings suggest that sperm can be affected by MG in the female reproductive organs, which may be associated with infertility.     

Changes in fertilization medium viscosity using hyaluronic acid impact bull sperm motility and acrosome status

The female reproductive tract, in particular the composition of the uterine and oviduct fluids, is responsible, at least in part, for triggering sperm cell modifications, essential for the acquisition of fertilization ability. Hyaluronic acid (HA) is a glycosaminoglycan present in these fluids, and its role in the fertilization process and sperm functionality is still barely understood. This work was designed to (a) determine the rheological characteristics of the fertilization medium by the addition of HA and (b) determine the HA influence on sperm motility and functional status. To that end, the in vitro fertilization medium was supplemented with 4 doses of HA (6, 60, 600 and 6,000 µg/ml) and analysed for viscosity and adhesion strength characteristics. Then, thawed semen from 6 bulls were incubated in these media and assessed at 4 different moments for morphological and functional parameters (plasma and acrosomal membrane integrities, mitochondrial membrane potential, capacitation, acrosomal reaction, and motility). The rheological evaluation showed that the addition of HA was able to increase both the viscosity and the adhesion strength of the fertilization medium, especially in the 6,000 µg/ml group in which the effect was more pronounced. No influence of HA could be observed on mitochondrial potential, and acrosomal and plasma membrane integrities. However, HA supplementation, at lower doses, led to an increase in the number of reacted sperm, as well as changes in motility parameters, with increase in the number of motile, rapid and progressive spermatozoa. In conclusion, the addition of HA alters the rheological properties of the fertilization medium and leads to the improvement of the properties related to sperm motility and capacitation, without compromising other functional aspects of the cell.     

Cytochrome c upregulation during capacitation and spontaneous acrosome reaction determines the fate of pig sperm cells: linking proteome analysis

To identify the mechanisms underlying capacitation, we undertook a high-resolution differential proteomic analysis of pig sperm cells. Two-dimensional gel electrophoresis and subsequent MALDI-TOF mass spectrometry analyses led to identification of 56 differentially expressed proteins. After induction of capacitation in vitro, the well-established markers of the capacitation (lactadherin P47, acrosomal protein SP-10 precursor, prohibitin, proteasomes, DJ-1 protein and arylsulfatase-A) and TCA cycle proteins (isocitrate dehydrogenase, malate dehydrogenase and pyruvate dehydrogenase) were identified. During induction, cytochrome c expression via the p53 pathway increased, however apoptotic executors, such as caspase-3, decreased significantly. Therefore, we tested the hypothesis that cytochrome c upregulation in spermatozoa is capable of activating tyrosine phosphorylation for capacitation, rather than apoptosis. Exposure of sperm cells to soluble Na2CrO4 [Cr (VI)], which induces cytochrome c upregulation, caused a dose- and time-dependent increase in tyrosine phosphorylation of sperm proteins in non-capacitating medium. In contrast, supplementation of cyclosporin A, which blocks cytochrome c upregulation, inhibited tyrosine phosphorylation of sperm proteins. Furthermore, spermatozoa in capacitation medium or non-capacitation media supplemented with soluble Cr (VI) showed similar levels of capacitation. These findings indicate that differential expression of many of these proteins has previously been unrecognized in sperm cells incubated in capacitation medium also suggest that a gradual increase of cytochrome c during incubation to induce capacitation determines sperm cell fate, i.e., apoptosis or further development for fertilization.     

Signalling Events and Associated Pathways Related to the Mammalian Sperm Capacitation

Capacitation is a biological phenomenon occurring prior to fertilization and is a multiple event process. Many physiological and biochemical changes takes place during the process; these changes are related to lipid composition of membrane, intracellular modulation of ion concentration, protein phosphorylation, sperm movement and membrane permeability. These events occur when the sperm is exposed to the new environment of ion concentration in the female reproductive tract. Ions such as bicarbonate and calcium facilitate capacitation by activating adenylyl cyclase, thus initiating protein kinase A (PKA) signalling cascade. Extracellular‐regulated kinase pathway is activated by ligand binding to the membrane receptors and intracellular activation by reactive oxygen species (ROS). Activation of these pathways leads to the phosphorylation of different proteins, which is associated with events such as capacitation, hyperactivation and acrosome reaction that are essential for successful fertilization. Extensive studies were carried out on protein phosphorylation in relation to capacitation, but its role still remains ambiguous.     

Premature capacitation of frozen-thawed spermatozoa from subfertile Japanese black cattle

Artificial insemination (AI) subfertility is an indication of failure of AI with frozen-thawed sperm classified as normal by conventional semen examination. Recently, 8 AI-subfertile Japanese Black cattle (S1-S8) were identified using the routine AI test or in vivo fertilization test, which included AI with frozen-thawed sperm of superovulated females and subsequent non-surgical recovery of presumptive zygotes. In the present study, we assessed capacitation states and in vitro oocyte penetration of frozen-thawed sperm from these bulls to estimate causal factors of AI subfertility. Frozen-thawed sperm from 8 AI-subfertile (S1-S8) and 9 fertile (F1-F9, control) bulls were washed and then used for a chlortetracycline (CTC) staining assay and in vitro fertilization test. The CTC staining assay revealed that approximately 50% of the sperm from 4 of the AI-subfertile bulls (S5-S8) were prematurely progressing into the capacitation state immediately after washing and resuspension in a CaCl(2)-lacking medium. In contrast, most of the sperm from the fertile bulls and other AI-subfertile bulls (S1-S4) remained uncapacitated. Addition of CaCl(2) to the medium effectively promoted a spontaneous acrosome reaction in the sperm samples from the AI-subfertile bulls (S5-S8). Moreover, the in vitro fertilization test showed that rates of sperm penetration into oocytes were significantly lower in sperm samples from the AI-subfertile bulls (S5-S8) than in the control sperm samples from the fertile bulls (F2-F4 and F7-F9). It has previously been suggested that prematurely capacitated sperm undergo a spontaneous acrosome reaction possibly due to uncontrolled influx of calcium ion, and consequently they possess relatively lower in vitro fertilizing ability. It is therefore possible that premature capacitation of sperm used for AI is a causal factor of subfertility of male Japanese Black cattle and a potentially good marker for identification of subfertile bulls for removal from AI programs.     

Changes in hyaluronidase, acrosin, and N-acetylhexosaminidase activities of dog sperm after incubation

Hyaluronidase, acrosin and N-acetylhexosaminidase activities were examined in sperm collected from 12 beagle dogs and in culture medium after 0.5 hr and 7 hr of sperm incubation. The activities of the three enzymes were significantly higher at 7 hr than at 0.5 hr (P < 0.05, 0.01), and the increases were associated with sperm capacitation. It was considered that the three enzymes in the dog sperm are related to fertilization by reason of the findings of the release of these enzymes from the sperm into the medium after 7 hr of incubation.