蜜蜂级型分化机理

蜜蜂是整个大自然生态系统中不可或缺的一部分,能有效地为多种植物和农作物授粉。蜜蜂是典型的真社会性昆虫,其生殖劳动分工现象有重要进化意义。而级型分化是导致劳动分工的一个重要因素,蜜蜂级型分化现象的机理研究已成为目前重要的研究热点之一。本文对近年来蜜蜂级型分化机理方面的研究进展进行了综述。国内外很多学者从营养、激素、基因表达、蛋白质和表观遗传等方面对蜜蜂级型分化机理进行了研究。蜂王浆中富含的57 kDa、蜂王幼虫期充足的食物量以及蜂王幼虫期高滴度的保幼激素(JH)和蜕皮激素(MA)等都可促进蜂王卵巢的发育以及诱导蜂王表型产生;而工蜂浆中富含的双香豆酸可诱使工蜂表型的产生。近年研究表明,表皮生长因子受体(Egfr)、胰岛素受体底物基因(Irs)、雷帕霉素基因(Tor)和甲基转移酶3(Dnmt3)等基因均可影响蜂王和工蜂的分化;蛋白质表达谱分析表明,不同时间点的蜂王幼虫和工蜂幼虫表达的差异蛋白质很多;表观遗传分析表明,DNA甲基化、microRNAs以及组蛋白乙酰化均是导致蜂王和工蜂级型分化的因素。此外,发育空间和蜂王浆均可通过调控基因的DNA甲基化水平影响蜜蜂幼虫的级型分化。     

表观遗传学与蜜蜂级型分化的研究进展

蜜蜂是一种高度社会化的昆虫,一个完整健康的蜂群通常是由蜂王、工蜂和雄蜂组成。尽管蜂王和工蜂的遗传物质相同,但它们在形态特征、行为职能和寿命方面表现出显著的差异。许多研究结果表明,营养因素是造成蜜蜂级型分化现象的主要原因,它可以影响蜂王幼虫和工蜂幼虫体内大量基因和蛋白的差异表达。随着表观遗传学的发展,人们对基因表达的调控机制有了新的认识,它与DNA甲基化、非编码RNA调控和组蛋白乙酰化等密切相关。这也为蜜蜂级型分化的分子机制提供了新的理论。本文就表观遗传学和蜜蜂级型分化的研究进展做一综述。     

LncRNA在蜜蜂级型分化中的功能研究

蜜蜂的级型分化被证实是由蜂王浆中的Royalactin决定,工蜂和蜂王幼虫在级型分化时编码基因的表达差异也被广泛研究.我们发现,在蜜蜂幼虫的级型分化过程中,lncRNA也有着显著的表达差异,因此认为,lncRNA也参与了蜜蜂的级型分化过程.进一步的分析显示,lncRNA可能通过影响上下游基因的转录和功能执行的方式,在蜜蜂早期发育的多细胞组织发育、神经系统发育和转录调控的过程中起到重要的调控作用.     

蜜蜂级型分化相关生理因子研究进展

蜜蜂Apis melliferaL.是典型的社会性昆虫,蜂群内蜂王和工蜂的级型分化现象吸引了众多研究者的高度关注。蜜蜂级型分化是一个极为复杂的生长发育调节过程,许多重要生理因子参与其中,包括保幼激素、蜕皮激素、胰岛素/胰岛素类似物信号通路等。本文概述了蜜蜂级型分化相关生理因子研究进展:保幼激素决定着蜜蜂级型发育的轨迹并能阻止卵巢发育过程中细胞的程序性死亡;蜕皮激素协同保幼激素发挥调节作用;蜜蜂蜂王与工蜂的躯体大小及相关器官大小的级型特异性差异与胰岛素/胰岛素类似物信号通路密切相关。此外,本文还介绍了蜜蜂级型分化模型,该模型系统描述了上述各生理因子对级型分化的综合作用。     

本期重点推介

正蜜蜂Apis spp.是具有级型分化的社会性昆虫。揭示其级型分化及调控机理,对认识社会性昆虫的演化形成机制、不同级型的发育和维持机理以及对其更好地加以应用均有重要的参考价值。已有研究表明,蜂王浆的主要蛋白成分———王浆主蛋白(major royal jelly proteins,MRJPs)在蜜蜂的级型分化中具有重要的功能。mrjp8是mrjps家族中较晚发现的一个成员。为了进一步明确mrjp8基因表达与蜜蜂级型分化的关系,福建农林大学蜂学学院李江红等对西方蜜蜂Apis mellifera不同发育龄期工蜂体内,以及成年工蜂、新出房蜂王和雄蜂不同组织中的mrjp8表达水平进行了检测,发现     

蜂王幼虫与工蜂幼虫发育期食物消耗量的研究

以意大利蜜蜂Apis mellifera ligustica雌性幼虫为试验材料,用鲜王浆、葡萄糖、果糖和酵母抽提物分别配制不同日龄的蜂王幼虫食物和工蜂幼虫食物,采用室内人工饲养蜜蜂幼虫技术饲养12h以内的蜂王幼虫和工蜂幼虫,直到幼虫出现排便和吐丝行为,记录幼虫生长发育期间消耗的总食物量。结果表明:1只蜂王幼虫在生长发育期平均消耗196.8mg蜂王幼虫食物,而1只工蜂幼虫在生长发育期平均消耗139.4mg工蜂幼虫食物。     

熊蜂级型分化研究进展

熊蜂是众多野生植物及农作物的有效授粉昆虫,具有重要的经济和生态价值。熊蜂复杂的生长发育过程及社会性使其成为社会生物学研究的最佳模式生物之一。社会性昆虫的生殖劳动分工具有重要的进化意义,而级型分化是形成生殖劳动分工的基础。蜜蜂级型分化的研究已取得诸多重要成果,其机理也得到了较为深入的阐释,而熊蜂的社会性研究尚未形成系统,与蜜蜂研究相差甚远。近来的研究表明,饲喂频率或者饲喂总量的差异能够引起熊蜂级型分化的发生。保幼激素和蜕皮激素与熊蜂幼虫的发育紧密联系,在熊蜂级型分化的过程中发挥重要作用。一些参与蜜蜂级型分化的基因,在熊蜂级型间也存在差异表达。此外,群体间的相互作用以及蜂王和工蜂间的竞争也是促进熊蜂级型分化发生的重要因素。本文从营养、激素调控、群体发展及相互作用等方面综述熊蜂级型分化机制,并对未来的研究提出可能方向。     

中华蜜蜂dynactin p62基因的克隆及不同发育阶段表达分析

为探究中华蜜蜂Apis cerana cerana dynactin p62基因的表达特性, 本研究克隆了中华蜜蜂dynactin p62的基因组DNA序列(GenBank登录号： JX101463) 和mRNA序列（GenBank登录号： JX101464）; 采用荧光定量PCR检测了中华蜜蜂dynactin p62在不同发育时期（3日龄和6日龄幼虫、 刚羽化出房蜜蜂）三型蜂中mRNA的表达量。结果表明： 该基因基因组DNA序列全长为2 403 bp, mRNA序列全长为1 491 bp, 编码496个氨基酸残基, 预测的蛋白分子量为56.49 kD, 等电点为8.31。系统发育分析表明中华蜜蜂dynactin p62与西方蜜蜂Apis mellifera dynactin p62聚成一支。该基因在不同发育时期均有表达, 在雌性蜜蜂（蜂王和工蜂）中, 刚羽化成虫期的表达量显著高于幼虫期(P<0.05), 并且同一发育时期相比, 工蜂的表达量显著高于蜂王(P<0.05); 而该基因在雄蜂中表达量没有明显的规律性。这些结果提示该基因可能与中华蜜蜂级型分化有关。     

意大利蜜蜂血淋巴HP19蛋白的表达及功能

昆虫血淋巴蛋白HP19主要参与蜕皮激素调控昆虫的变态及发育进程,蜂群内的工蜂、蜂王和雄蜂具有不同的变态和发育历期,为探究hp19在调控意大利蜜蜂Apis mellifera ligustica三型蜂变态发育中的作用,本研究利用实时荧光定量PCR技术对hp19在不同发育时期的工蜂、雄蜂和蜂王体内的转录水平进行检测。结果表明,该基因在工蜂和雄蜂3龄幼虫体内表达量分别为参照基因的104和105倍,在5龄幼虫体内的表达则分别降为参照的10和102倍,蛹期表达量又都显著提高。hp19在蜂王整个幼虫期的表达保持在参照的102倍,封盖后逐渐上升,至化蛹前达到参照的105倍。在成年工蜂体内的表达为参照的104倍,而在新羽化蜂王和雄蜂体内表达水平为参照的107倍,但在性成熟的产卵蜂王和雄蜂体内的表达显著降低至参照的104倍。hp19在三型蜂体内这种不同的表达模式说明其不仅与三型蜂差异的变态发育历期有关,还可能与雄蜂和蜂王的生殖有关,具有多样的生物学功能。     

意蜂SOD和POD同工酶在工蜂、雄蜂和蜂王之间的比较

用聚丙烯酰胺凝胶电泳的方法,以意大利蜜蜂工蜂、雄蜂和蜂王以及两种不同大小幼虫之间的超氧化物歧化酶(SOD)和过氧化物酶(POD)同工酶分别作了比较。结果表明,这2种同工酶在意蜂幼虫阶段与成体阶段均有明显差异;意蜂工蜂、雄蜂和蜂王都有着不同的同工酶谱型。说明意蜂同工酶在种内的表达受到发育程度、进食质量、分化方向等因素的影响。     

黑胸散白蚁幼期不同品级的发育和分化

在黑胸散白蚁Reticulitermes chinensis发育和分化过程中,发现有假工蚁、假若蚁两种虫态。假工蚁由6龄和7龄工蚁转化发育而来,假若蚁由4龄和5龄若蚁转化发育而来。显微测量结果表明,黑胸散白蚁的胚后发育主要包括2个龄期的幼蚁期、6个以上龄期的工蚁期、4个龄期的若蚁期和有翅成虫。在此基础上分析了其他虫态的分化来源,发现兵蚁由3～7龄工蚁分化发育而来,翅鳞型和长翅芽型补充生殖蚁由6龄若蚁转化发育而来,短翅芽型补充生殖蚁由4龄和5龄若蚁转化发育而来,微翅芽型补充生殖蚁既可由4～6龄工蚁转化发育而来,又可由假工蚁和假若蚁转化发育而来,无翅型补充生殖蚁由3～7龄工蚁转化发育而来。提出了黑胸散白蚁群体中不同品级个体的可能分化途径。     

Juvenile-hormone-dependent interaction of actin and spectrin is crucial for polymorphic differentiation of the larval honey bee ovary

Programmed cell death in the worker ovary of Apis mellifera reduces the number of ovarioles during metamorphosis from 150-200 primordia to less than 10. In contrast, practically all ovarioles in the ovary of queens survive to the adult stage. The correct formation and persistence of polyfusomes has been suggested as a critical factor for ovariole survival. We have analyzed the developmental dynamics of F-actin and alpha-spectrin in fusomes of queen and worker larvae, and in juvenile-hormone-treated worker larvae. Small fusomes containing actin and spectrin can be detected in the ovaries of fourth instar larvae in both castes. After molting to the fifth instar, the actin-spectrin association persists in the enlarged fusomes of queen ovarioles. In workers, actin dissociates from the fusomal and cortical alpha-spectrin. Coinciding with the appearance of apoptosis markers, large agglomerates of actin are detectable in worker ovarioles. Treatment of fourth-instar worker larvae with juvenile hormone rescues ovarioles from apoptosis and maintains the actin-spectrin association. Juvenile-hormone-dependent actin-spectrin interaction is thus one of the earliest steps in the differentiation of a polymorphic ovary. Plasticity in ovariole numbers as a result of hormone-dependent fusome formation may be a more widespread phenomenon in insects, extending beyond caste polymorphism in highly eusocial Hymenoptera.     

黑胸散白蚁幼期不同品级的发育和分化

在黑胸散白蚁Reticulitermes chinensis发育和分化过程中,发现有假工蚁、假若蚁两种虫态。假工蚁由6龄和7龄工蚁转化发育而来,假若蚁由4龄和5龄若蚁转化发育而来。显微测量结果表明,黑胸散白蚁的胚后发育主要包括2个龄期的幼蚁期、6个以上龄期的工蚁期、4个龄期的若蚁期和有翅成虫。在此基础上分析了其他虫态的分化来源,发现兵蚁由3～7龄工蚁分化发育而来,翅鳞型和长翅芽型补充生殖蚁由6龄若蚁转化发育而来,短翅芽型补充生殖蚁由4龄和5龄若蚁转化发育而来,微翅芽型补充生殖蚁既可由4～6龄工蚁转化发育而来,又可由假工蚁和假若蚁转化发育而来,无翅型补充生殖蚁由3～7龄工蚁转化发育而来。提出了黑胸散白蚁群体中不同品级个体的可能分化途径。     

mRNA expression and DNA methylation in three key genes involved in caste differentiation in female honeybees(Apis mellifera)

In honeybee(Apis mellifera)colonies,queens and workers are alternative forms of the adult female honeybee that develop from genetically identical zygotes but that depend on differential nourishment.Queens and workers display distinct morphologies,anatomies and behavior,better known as caste differentiation.Despite some basic insights,the exact mechanism responsible for this phenomenon,especially at the molecular level,remains unclear although some progress has been achieved.In this study,we examined mRNA levels of the TOR(target of rapamycin)and Dnmt3(DNA methyltransferase 3)genes,closely related to caste differentiation in honeybees.We also investigated mRNA expression of the S6K(similar to RPS6-p70-protein kinase)gene linked closely to organismal growth and development in queen and worker larvae(1-day and 3-day old).Last,we investigated the methylation status of these three genes in corresponding castes.We found no difference in mRNA expression for the three genes between 1st instar queen and worker larvae;however,3rd instar queen larvae had a higher level of TOR mRNA than worker larvae.Methylation levels of all three genes were lower in queen larvae than worker larvae but the differences were not statistically significant.These findings provide basic data for broadening our understanding of caste differentiation in female honeybees.     

Reproductive skew and the origin of sterile castes

Reproductive skew theory has not heretofore formally addressed one of the most important questions in evolutionary biology: How can whole-life sterile castes evolve? We construct a transactional skew model investigating under what conditions a subordinate in a multimember group is favored to develop into a morphologically specialized worker caste. Our model demonstrates that, contrary to former expectations, the ecological and genetic conditions favoring caste differentiation are far more restrictive than those favoring high skew. Caste differentiation cannot be selected in saturated, symmetrical relatedness groups unless the genetic relatedness among group members is extremely high. In contrast, it can be selected in the saturated, asymmetrical relatedness (parent-offspring) groups with complete skew. If we also consider the future reproduction of subordinates, caste differentiation is possible only after the group size reaches a certain critical point. Most importantly, caste differentiation in a parent-offspring group increases its saturated group size. The positive feedback between group size and the degree of caste differentiation can continue in principle until completely sterile worker castes emerge. Thus, at least in the case of parent-offspring groups, group size but not the degree of reproductive skew may be a better index of the level of social complexity. A scheme for the evolution of sterile worker castes that integrates the role of group size into the framework of reproductive skew theory is proposed.     

Wing disc development during caste differentiation in the ant Pheidole megacephala (Hymenoptera: Formicidae)

The genus Pheidole has three distinct castes in females: queen, major, and minor workers. It has been believed that the larvae of major workers have prominent mesothoracic wing discs, although the minor worker larvae lack them. Here we conducted histological examinations of wing discs during larval development in P. megacephala. We show that all three castes have mesothoracic wing discs, at least in their early stage of the final larval instar, and that the wings degenerate differently in the dimorphic worker castes. The minute wing discs of minor workers neither grow nor metamorphose but disappear during the prepupal stage. On the contrary, the wing discs of major workers evaginate at the onset of the prepupal stage but subsequently degenerate by apoptotic cell death. This apoptotic wing degeneration in the prepupal stage was contradistinguished from wing degeneration in some lepidopteran insects, in which apoptosis occurs in the pupal wing buds. Our results suggest that each worker caste shows a different degeneration process to express the wingless character and that apoptotic degeneration has been adopted in association with the evolution of worker dimorphism.     

Development of non-reproductive castes in the neotropical termite generaCornitermes,Embiratermes andRhynchotermes (Isoptera,Nasutitermitinae)

Summary The developmental pattern of the neuter castes was studied in the mandibulate nasute generaCornitermes, Embiratermes andRhynchotermes. InCornitermes walkeri, all the workers and soldiers are male. There are two larval and a single worker instar. Workers can molt into presoldiers. InEmbiratermes chagresi andRhynchotermes perarmatus, both sexes are present among the neuters. A slight sexual dimorphism (males > females) is discernible among both larval instars and among workers ofE. chagresi; female workers can molt into presoldiers. InR. perarmatus, the sexual dimorphism is conspicuous from the first larval instar on. Male larvae go through two instars, then give rise to workers, which do not molt. InR. perarmatus, there is no worker stage in females, but a third larval instar, preceding the presoldier. Hypotheses are proposed as to the evolution of these caste patterns, attempting to conciliate present knowledge of Nasutitermitinae phylogeny and known evolutionary trends affecting termite caste patterns, according to the species' ecology.Research Associate: National Fund for Scientific Research (Belgium).     

Gene expression patterns associated with caste and reproductive status in ants: worker‐specific genes are more derived than queen‐specific ones

Variation in gene expression leads to phenotypic diversity and plays a central role in caste differentiation of eusocial insect species. In social Hymenoptera, females with the same genetic background can develop into queens or workers, which are characterized by divergent morphologies, behaviours and lifespan. Moreover, many social insects exhibit behaviourally distinct worker castes, such as brood‐tenders and foragers. Researchers have just started to explore which genes are differentially expressed to achieve this remarkable phenotypic plasticity. Although the queen is normally the only reproductive individual in the nest, following her removal, young brood‐tending workers often develop ovaries and start to reproduce. Here, we make use of this ability in the ant Temnothorax longispinosus and compare gene expression patterns in the queens and three worker castes along a reproductive gradient. We found the largest expression differences between the queen and the worker castes (~2500 genes) and the smallest differences between infertile brood‐tenders and foragers (~300 genes). The expression profile of fertile workers is more worker‐like, but to a certain extent intermediate between the queen and the infertile worker castes. In contrast to the queen, a high number of differentially expressed genes in the worker castes are of unknown function, pointing to the derived status of hymenopteran workers within insects.     

黑胸散白蚁下唇腺的解剖和扫描电镜观察

【目的】通过研究黑胸散白蚁Reticulitermes chinensis下唇腺解剖构造及其在不同品级个体间的分化,为进一步探索口交哺和品级分化机制提供参考。【方法】通过显微解剖观察,了解黑胸散白蚁下唇腺的形态构造及其在不同品级个体间的分化;通过扫描电镜观察,了解下唇腺的结构及神经支配;通过饮水实验,研究工蚁饮水及下唇腺囊的贮水功能。【结果】黑胸散白蚁下唇腺是左右对称结构,每侧构造由一个下唇腺腺泡群、一个下唇腺囊及相关的导管组成。每侧导管分别开口于舌基部下方。蚁后的下唇腺最发达,在下唇腺大小、下唇腺囊大小、腺泡大小及腺泡数量4方面均显著高于其他品级个体;兵蚁、工蚁、有翅成虫的下唇腺也较为发达,相互之间这4个参数的差异性不显著。扫描电镜观察发现,工蚁下唇腺腺泡由主导管和分支导管相连,腺泡外侧有神经分布。黑胸散白蚁工蚁有饮水习性,获得的水贮存在下唇腺囊内。【结论】黑胸散白蚁不同品级个体间,蚁后的下唇腺最发达,有翅成虫的下唇腺也比较发达,说明蚁后除行使生殖职能外,还承担交哺育幼等职能。黑胸散白蚁工蚁有饮水习性,下唇腺囊有贮水功能。