斑马鱼性腺发育的组织学观察

在过去几十年,斑马鱼(Danio rerio)由于其发育周期短且速度快,胚胎发育透明,已经成为众多研究领域的典型模式生物.斑马鱼的性腺发育和分化非常特殊,雄性和雌性幼鱼的性腺在早期全部发育成"类卵巢"结构.目前,对于斑马鱼的性别分化和性腺分化机制还不清楚.本文以孵化后不同时期的斑马鱼仔鱼和幼鱼的生殖腺为材料,经石蜡切片和苏木精染色后,荧光显微镜下观察了斑马鱼仔鱼性腺从出现、分化到成熟的发育过程.结果发现:孵化后5～10日龄仔鱼腹腔两侧可以观察到没有分化的生殖腺,其中的生殖细胞明显比周围的体细胞大;孵化后14～24日龄仔鱼的生殖腺中可见由卵原细胞分裂形成的生殖包囊,其中的生殖细胞进一步分化、分裂形成体积更大、数量更多的卵母细胞;25日龄左右的仔鱼,其性腺成为在腹腔两侧对称,而且在组织结构上也较为典型的卵巢样结构.到35日龄前后可见一部分仔鱼的性腺逐步由卵巢样结构向精巢结构转变的过程.我们在2周左右的仔鱼的性腺中观察到了生殖包囊存在,这一现象还未见有前人报道.在本试验中,我们不仅清楚地观察到类似卵巢的性腺中"卵母细胞"逐渐凋亡消失的过程,还观察到性腺由最初的类似卵巢样结构逐渐变成典型的精巢结构的整个过程.这些研究成果将为发育生物学提供有价值的信息和第一手资料.     

泽蛙的性腺分化及温度对性别决定的影响

通过组织学方法观察了泽蛙(Rana limnocharis)原始生殖细胞(PGCs)的迁移、原始性腺的形成和性腺分化,并且探讨在不同的培育温度条件下性腺分化的差异。泽蛙的性腺分化有其特殊性:生殖嵴形成时,其中既有体细胞,又有原生殖细胞;无论原始性腺是分化成为精巢还是卵巢,其中都出现一个初生性腔。蝌蚪孵化后的17-34d(Gosner 26-38期)为性腺分化的敏感时期。在蝌蚪孵化后的第2d(Gosner 25期),分别用不同水温18℃±1℃、30℃±1℃、32℃±1℃、34℃±1℃培育蝌蚪,直至完成变态幼蛙(Gosner 46期)形成。自然水温23℃-25℃为对照。对照组的雌、雄性比接近1∶1(1∶1.06);18℃±1℃实验组的雌、雄比例为1.83∶1,雄性率仅35.1%(P<0.01);从30℃±1℃实验组起,雄性率提高,34℃±1℃实验组的雄性率达74.0%(P<0.01)。较高的培育温度可使泽蛙蝌蚪性别分化趋向雄性,而较低的培育温度则使蝌蚪雌性化。泽蛙的性别分化属于温度依赖型性决定(TSD)。当前全球性气候变暖对两栖类性比的稳定存在着威胁。     

革胡子鲇原始生殖细胞的起源、迁移及性腺分化

革胡子鲇又称埃及胡子鲇,是一种多次产卵类型的硬骨鱼。作者用组织学、组织化学、电子显微镜等方法对革胡子鲇的原始生殖细胞(Primordial germ cells,PGCs)的起源、特征、迁移方式和性腺分化进行了研究。实验结果:PGCs来源于内胚层;PGCs的细胞质中存在着一种与生殖细胞有关的电子致密物--生殖质(Germ plasm);PGCs在迁移过程中有主动迁移的能力;PGCs到达生殖嵴的部位后,与生殖上皮细胞(Epithelisl cells)一起共同形成原始性腺;原始性腺分别逐步向精巢和卵巢分化;生殖质与性腺的分化有密切关系;卵巢的分化比精巢早。       

小鼠生殖细胞的胚胎发育

本文综述了近年来小鼠胚胎发育过程中生殖细胞的起源、迁移与增殖、性别分化及其基因组修饰等方面的研究进展。小鼠生殖细胞在7~7.5dpc时由原始生殖细胞（PGC）演变而来,至12.5dpc时PGC全部迁移进入生殖嵴,到13.5dpc时停止分裂。Steel/c-kit信号途径在PGC迁移过程中起重要作用。生殖细胞的性别主要是由生殖腺中体细胞的微环境决定的。Y染色体上存在精子形成所必需的基因。生殖细胞的全基因组范围的重新甲基化晚于胚胎体细胞的重新甲基化,到18.5dpc时才完成。雌性生殖细胞的X染色体重新活化在14.5~15.5dpc时完成,并且与生殖嵴的性别分化无关。 Abstract:This paper reviewed the recent progress of the origin,migration and proliferation,sex determination,and genomic modification of murine germ cells during its embryonic development. Murine germ cells originate from primordial germ cells at about 7~7.5dpc. Then PGCs migrated into germinal ridge at about 12.5dpc during which Steel/c-kit signal pathway plays important roles and stopped division at 13.5dpc. The sex of germ cells was mainly determined by the soma microenvironment in the gonad. And there are essential genes for sperm formation on the Y chromosome. The de novo methylation of murine germ cells was much later than soma cells and was completed at about 18.5dpc. The X chromosome reactivation of female germ cells was finished at about 14.5~15.5dpc which was independent of sexual differentiation of germinal ridge.     

黄鳝性腺自然逆转过程中vasa基因的表达分析

本研究采用RNA反义探针原位杂交技术,对vasa基因在黄鳝(Monopterusalbus)性腺发育过程中的表达情况进行了分析。结果表明:vasamRNA在Ⅰ、Ⅱ、Ⅲ期卵母细胞的胞质中均匀分布,在Ⅳ、Ⅴ期卵母细胞中vasamRNA有向胞质外周皮层迁移集中的趋势,但不明显;退化的卵粒也呈现vasamRNA阳性反应;在Ⅲ、Ⅳ期卵巢的被膜中检测到带有vasa阳性信号的细胞,这些细胞可能是待向精原细胞分化、迁移到卵巢被膜上的原始生殖细胞(Primordialgermcell,PGC),在性逆转过程中这些PGC可能由卵巢被膜迁移到精小叶中并发育成精子;在成熟精巢中,vasa在精原细胞和初级精母细胞中表达。进一步采用碱性磷酸酶染色法分析黄鳝卵巢及精巢后发现:在卵巢中,除了卵母细胞外,卵巢被膜中也检测到了带有碱性磷酸酶阳性信号的细胞;在成熟精巢中,只在生殖腺囊内的雄性生殖细胞中检测到碱性磷酸酶,而精巢被膜中没有检测到带有碱性磷酸酶阳性信号的细胞。本研究结果初步表明:黄鳝的雄性生殖细胞可能起源于雌性阶段卵巢被膜中的原始生殖细胞[动物学报51(3):469-475,2005]。     

中华鳖性腺的发生与发育研究

为了揭示中华鳖性腺的发生与发育规律,在(32±0.5)℃温度下孵化鳖卵,72h时,从组织切片中可见原始生殖细胞移向中肠附近的内胚层;第5天生殖嵴形成;第13天性腺分化为皮质和髓质;第16天性腺开始分化为精巢或卵巢,至第22天时分化结束,形成精巢或卵巢.胚胎期、稚鳖和1龄鳖的性腺均呈短细管状,表面光滑,无色,胶状透明;2龄、3龄、4龄鳖的精巢呈长椭圆形.稚鳖的卵巢发育至卵原细胞期,组成精巢的曲细精管不明显,管内为精原细胞;1龄幼鳖的卵巢发育至初级卵泡期,精巢的曲细精管内精原细胞的数量增加;2龄和3龄鳖的卵巢处于生长卵泡期,3龄末的卵巢内可见到成熟卵泡,2龄鳖的曲细精管内出现初级精母细胞,3龄末的曲细精管开始出现精细胞和精子;4龄鳖的卵巢发育至成熟卵泡期,曲细精管内由管壁向管腔依次为精原细胞、初级精母细胞、次级精母细胞、精细胞和精子.结果表明,在(32±0.5)℃温度下,鳖胚发育至22d时,精巢或卵巢形成;在自然条件下,中华鳖至4龄时,性腺才完全发育成熟.     

黄颡鱼性腺分化的组织学观察

运用组织学方法,观察黄颡鱼(Pelteobagrus fulvidraco)性腺分化过程.结果表明,在水温(20±1)℃条件下,卵巢分化时间明显早于精巢.卵巢分化最早发生于孵出后13 d左右,其主要标志为原始性腺横切面上出现一个组织突起,进而形成卵巢腔;精巢分化的最早标志为精小叶和输精管的形成,开始于孵出后55 d.在发育早期,雌性生殖细胞的活动及分化明显早于雄性生殖细胞.孵出后25 d,卵原细胞开始通过有丝分裂快速增殖,孵出后34 d左右进入成熟分裂阶段;精原细胞在孵出后55 d时才开始大量增殖,成熟分裂最早发生于孵出后64 d.     

中国大鲵生殖腺胚后发育的形态学观察

为探寻中国大鲵(Andrias davidianus)生殖腺胚后发育的特点及规律,采用解剖学与组织学技术对其形态结构变化进行了观察.结果表明,大鲵的原始生殖腺开始出现于出膜28～49 d;出膜133～175 d时一些个体生殖腺内已初步分化出原始卵泡;出膜259 ～343 d时一些个体生殖腺内已初步分化出生精小叶;出膜427 d时,卵巢已明显分化为皮质与髓质,且髓质内出现了卵巢腔,精巢内生精小叶及其内的腔隙、精巢间质等分化已较为明显;出膜511 d时精巢分化为明显的生精小叶和非成熟小叶两个区域.本文认为,大鲵与其他无羊膜类原始生殖腺的分化一般发生在胚后阶段,而且雌性的分化时间早于雄性.     

棘胸蛙的性腺分化及温度对其性别决定的影响

单性养殖在棘胸蛙(Quasipaa spinosa)养殖中意义显著。为了了解棘胸蛙性腺分化,并探讨在不同的培育温度条件下性腺分化的差异。通过组织切片观察了棘胸蛙原始性腺的形成和性腺分化。棘胸蛙的性腺分化有其特殊性:生殖嵴形成时,其中既有体细胞,又有原始生殖细胞(PGCs);无论原始性腺是分化成为精巢还是卵巢,其中都出现一个带有单层扁平上皮初生性腔,当单层扁平上皮逐渐消失后形成次生性腔。性腔周围的PGCs开始长大2—3倍时,性腺将分化成为卵巢;体细胞渗入性腔中,使腔隙变小直至消失,这种原始性腺分化成为精巢。棘胸蛙蝌蚪孵化后的l7—80 d(Gosner 25—26期)为性腺分化的敏感时期。实验选取同一批次刚孵出蝌蚪(Gosner 24期),分别用不同水温(16±1)℃、(27±1)℃、(31±1)℃3组实验组及自然水温(23±1)℃对照组条件下的培育蝌蚪。结果显示,对照组的雌、雄性比为26∶24,雄性率接近50%;(16±1)℃实验组的雌、雄比例为33∶17,雄性率仅34%(P0.05);从(27±1)℃实验组起,雄性率提高,(31±1)℃实验组的雄性率达70%(P0.05)。棘胸蛙的性别分化属于温度依赖型性决定(TSD)。较高的培育温度可使棘胸蛙蝌蚪性别分化趋向雄性,而较低的培育温度则使蝌蚪雌性化。     

小鼠卵巢几个重要发育事件的初步研究

选定多个阶段小鼠卵巢进行切片染色和生殖细胞计数统计等分析,以发现该阶段小鼠卵巢的发育特点。结果显示在胚胎发育第12.5 d的生殖嵴中,大部分的生殖细胞正进行有丝分裂增殖,并以生殖包囊的形式存在;在出生后第2 d的小鼠卵巢中,有大量紧密接触的原始卵泡,表明生殖包囊刚完成重组形成原始卵泡;在第5 d的小鼠卵巢中,原始卵泡仍占有大部分比例,但也有大量的初级卵泡处于发育之中;在出生后第10 d的卵巢中同时有原始卵泡、初级卵泡和次级卵泡的发育;老年小鼠(16个月大)卵巢中已基本没有卵母细胞。     

Sexual Cannibalism as a Manifestation of Sexual Conflict

Sexual cannibalism is a well-known example for sexual conflict and has many facets that determine the costs and benefits for the cannibal and the victim. Here, I focus on species in which sexual cannibalism is a general component of a mating system in which males invest maximally in mating with a single (monogyny) or two (bigyny) females. Sexual cannibalism can be a male strategy to maximize paternity and a female strategy to prevent paternity monopolization by any or a particular male. Considerable variation exists between species (1) in the potential of males to monopolize females, and (2) in the success of females in preventing monopolization by males. This opens up exciting future possibilities to investigate sexually antagonistic coevolution in a largely unstudied mating system.Sexual cannibalism, the killing and consumption of potential or actual mating partners in a mating context, has been termed a “pinnacle of sexual conflict” because of the dramatic ending of the act for one mating partner, mostly the male (Elgar and Schneider 2004). This contradiction of traditional sex roles may be one reason why the phenomenon of sexual cannibalism has intrigued naturalists for a long time. In the context of sexual conflict, sexually cannibalistic behavior of females is a harmful trait, and antagonistic traits are expected to evolve in males, which can be considered the reverse of most other examples in which females respond to male harm (see Perry and Rowe 2014). I will discuss potential antagonistic traits to sexual cannibalism in males but will also show that the above view is too simplistic when it comes to spider mating systems characterized by very low male mating rates.It is important to note that there are different kinds of sexual cannibalism based on very different evolutionary scenarios (Elgar and Schneider 2004; Prenter et al. 2006; Wilder et al. 2009). The most extreme divide exists between cannibalism before sperm transfer, which can only benefit the cannibal, and sexual cannibalism during or after sperm transfer (from here on termed postinsemination sexual cannibalism), which can benefit the cannibal and the victim (Elgar and Schneider 2004). Despite a longer history of research on preinsemination sexual cannibalism, the evolutionary causes and consequences of postinsemination sexual cannibalism are generally less debated.There are reports (often anecdotal) on the occurrence of sexual cannibalism from diverse invertebrate taxa (Elgar 1992) and it may well occur in all predatory invertebrates that are potentially cannibalistic (Polis 1981). It is beyond the scope of this brief review to list and evaluate all reported occurrences. Rather, I will start with a brief account of the generally discussed causes and consequences of sexual cannibalism and will then concentrate on the conflicting interests of the sexes regarding postinsemination sexual cannibalism in mating systems that are characterized by very low male mating rates.Studies that investigate sexual cannibalism experimentally are mostly concerned with (1) nutritional aspects, (2) the importance of sexual size dimorphism and sexual selection, and, increasingly, (3) behavioral syndromes. The aggressive spillover hypothesis suggests that preinsemination sexual cannibalism is part of a behavioral syndrome in which aggression against mating partners spills over from a foraging context (Arnqvist and Henriksson 1997). There is mixed support for this idea in the few species that have been looked at. In several spider species, females consistently differ in their aggressiveness and these differences affect sexual cannibalism (for a recent debate about the evidence for this hypothesis, see Johnson 2013; Kralj-Fišer et al. 2013b; Pruitt and Keiser 2013).A majority of studies have taken a unilateral view and have been concerned with the “motivation” of the cannibal; because sexual cannibalism generally occurs in predators, hunger is a well-supported motivation (Wilder et al. 2009). Many predators are food-limited, and, assuming a trade-off between foraging and mating, the balance may tilt toward foraging under particular circumstances (modeled by Newman and Elgar 1991). Food and mate availability will influence the costs and benefits of sexual cannibalism for females and have been one focus of a recent review on sexual cannibalism (Wilder et al. 2009).In all predatory and cannibalistic animals, mating partners impose selection on each other’s abilities to avoid or resist aggression. This selection pressure is asymmetrical if one sex is physically dominant. Indeed, the differences in size between females and males often determine the frequency of sexual cannibalism, perhaps because the potential to resist a cannibalistic attack is size-dependent (Elgar 1992; Wilder and Rypstra 2008). Usually, males are the victims and females are the cannibals. Yet, reversed sexual cannibalism has also been reported and appears to be associated with the reversed pattern in sexual size dimorphism. Examples are the water spider, Arygoneta aquatica (Schutz and Taborsky 2005, 2011) and role-reversed wolf spiders (Aisenberg et al. 2011). In the gnaphosid spider, Micaria sociabilis, large, young males cannibalize old and relatively smaller females (Sentenska and Pekar 2013). These examples further support the notion that the relative size differences of a mating pair play a part in determining the likelihood of sexual cannibalism. Patterns can be found both on a between-species comparative scale and on a within-species scale (Wilder and Rypstra 2008; Wilder et al. 2009), and they are also reported as an underlying pattern in cannibalism outside a mating context (Bleakley et al. 2013). Furthermore, there is anecdotal evidence for the same pattern in hermaphrodites (e.g., Goto and Yoshida 1985; Michiels et al. 2003), which may constitute a particularly interesting case to study, as the power asymmetries are less obviously related to the male or female role.In asymmetric encounters, the costs and risks of aggressive behavior toward potential mating partners are low for the dominant partner. Toward smaller males, females could use aggressiveness as a means of partner choice. Indeed, many studies suggest that sexual selection in addition to gaining a meal may be the adaptive value of sexual cannibalism (Prenter et al. 2006). From the female perspective, aggressive behavior directed toward males may serve as a general screening of partner quality, a mechanism often described as indirect mate choice (Elgar and Nash 1988; Prenter et al. 2006; Kralj-Fišer et al. 2012). A screening method implies that females attack every male, and suitors that cannot withstand and persist an attack will be killed and consumed; alternatively, females may differentiate between males and attack and consume only those males that do not meet certain quality criteria (reviewed in Prenter et al. 2006). The latter has been found in wolf spiders (Wilgers and Hebets 2012). The latter mechanism of direct choice is more complex than the indirect one as it requires perception and assessment of quality cues, and large enough benefits of choosiness are expected to match the costs. Mate rejection via sexual cannibalism is considered a particularly extreme case of sexual conflict mostly because rejection can lead to death. Although this may be true for the individual male that loses all future reproductive success, frequencies of preinsemination sexual cannibalism might be rather low (Kralj-Fišer et al. 2013b). Please note that in almost every species, a certain proportion of individuals will be excluded from the mating market and will have no mating success. The claim that prevention of mating success via sexual cannibalism results in more intense sexual conflict than exclusion from mating with less drastic measures has, to my knowledge, never been tested. Because of the scarcity of data on natural frequencies of preinsemination cannibalism, a meta-analysis would not reveal a realistic picture at this stage. Hence, to date, it is not feasible to compare the relative strength of selection imposed by a cannibalistic mate choice strategy against a strategy with less drastic consequences of mate rejection. More studies are needed to unravel the exact nature of sexual selection under the threat of ending as a meal. Below, I will briefly sketch possible responses to selection imposed by sexually cannibalistic females before or during insemination.     

The Relationship between Sexual Selection and Sexual Conflict

Evolutionary conflicts of interest arise whenever genetically different individuals interact and their routes to fitness maximization differ. Sexual selection favors traits that increase an individual’s competitiveness to acquire mates and fertilizations. Sexual conflict occurs if an individual of sex A’s relative fitness would increase if it had a “tool” that could alter what an individual of sex B does (including the parental genes transferred), at a cost to B’s fitness. This definition clarifies several issues: Conflict is very common and, although it extends outside traits under sexual selection, sexual selection is a ready source of sexual conflict. Sexual conflict and sexual selection should not be presented as alternative explanations for trait evolution. Conflict is closely linked to the concept of a lag load, which is context-dependent and sex-specific. This makes it possible to ask if one sex can “win.” We expect higher population fitness if females win.Many published studies ask if sexual selection or sexual conflict drives the evolution of key reproductive traits (e.g., mate choice). Here we argue that this is an inappropriate question. By analogy, G. Evelyn Hutchinson (1965) coined the phrase “the ecological theatre and the evolutionary play” to capture how factors that influence the birth, death, and reproduction of individuals (studied by ecologists) determine which individuals reproduce, and “sets the stage” for the selective forces that drive evolutionary trajectories (studied by evolutionary biologists). The more modern concept of “eco-evolutionary feedback” (Schoener 2011) emphasizes that selection changes the character of the actors over time, altering their ecological interactions. No one would sensibly ask whether one or the other shapes the natural world, when obviously both interact to determine the outcome.So why have sexual conflict and sexual selection sometimes been elevated to alternate explanations? This approach is often associated with an assumption that sexual conflict affects traits under direct selection, favoring traits that alter the likelihood of a potential mate agreeing or refusing to mate because it affects the bearer’s immediate reproductive output, whereas “traditional” sexual selection is assumed to favor traits that are under indirect selection because they increase offspring fitness. These “traditional” models are sometimes described as “mutualistic” (e.g., Pizzari and Snook 2003; Rice et al. 2006), although this term appears to be used only when contrasting them with sexual conflict models. The investigators of the original models never describe them as “mutualistic,” which is hardly surprising given that some males are rejected by females.In this review, we first define sexual conflict and sexual selection. We then describe how the notion of a “lag load” can reveal which sex currently has greater “power” in a sexual conflict over a specific resource. Next, we discuss why sexual conflict and sexual selection are sometimes implicitly (or explicitly) presented as alternative explanations for sexual traits (usually female mate choice/resistance). To illustrate the problems with the assumptions made to take this stance, we present a “toy model” of snake mating behavior based on a study by Shine et al. (2005). We show that empirical predictions about the mating behavior that will be observed if females seek to minimize direct cost of mating or to obtain indirect genetic benefits were overly simplistic. This allows us to make the wider point that whom a female is willing to mate with and how often she mates are often related questions. Finally, we discuss the effect of sexual conflict on population fitness.     

Sexual selection

Sexual selection is a concept that has probably been misunderstood and misrepresented more than any other idea in evolutionary biology, confusion that continues to the present day. We are not entirely sure why this is, but sexual politics seems to have played its role, as does a failure to understand what sexual selection is and why it was initially invoked. While in some ways less intuitive than natural selection, sexual selection is conceptually identical to it, and evolution via either mechanism will occur given sufficient genetic variation. Recent claims that sexual selection theory is fundamentally flawed are simply wrong and ignore an enormous body of evidence that provides a bedrock of support for this major mechanism of organic evolution. In fact it is partly due to this solid foundation that current research has largely shifted from documenting whether or not sexual selection occurs, to addressing more complex evolutionary questions.     

性反转

性反转(sex reversal)是指生物个体从一种性别特征转变为另一种相反的性别特征的性别转变现象。性反转只有雌雄异体的生物才会出现的现象,雌雄同体的生物并没有此类现象发生。性反转有2种类型：1)获得性性反转：此类性反