嗅觉研究进展--2004年诺贝尔生理学或医学奖获奖工作简介

2004年度诺贝尔生理学或医学奖授予了两位美国神经生理学家：Richard Axel和Linda B．Buck,以表彰他们在嗅觉研究中所作出的贡献。他们证明啮齿类动物大约有1000种不同类型的嗅觉受体基因超家族,文章发表在1991年“细胞”上。随后他（她）们对嗅觉信号在脑内的传递、修饰和加工进行了深入的研究。由于他们的研究使人们对嗅觉的认识,产生了一个飞跃。本文就这方面的进展作一简要的介绍。     

两种功能气味受体在同一神经元中共表达

嗅觉研究领域的基本原则之一是每个嗅觉受体神经元(ORN)表达单一的嗅觉受体。但是,耶鲁大学的J.R.Carlson的实验室构建了果蝇下颚须的完整的嗅觉受体与神经元的关系图谱,发现2种受体基因共表达于同一类ORN中。Goldman等人经RT-PCR和原位杂交发现了7种气味受体基因,而果蝇的上颚须仅有6类ORN,由此他们提出至少有一类ORN中表达多于一种气味受体基因的假说。研究者通过运用GAL4-UAS表达体系,原位杂交技术和缺失气味受体基因的ORN的果蝇突变体发现基因Or33c和Or85e共表达于pb2A类的ORN中,而且这种共表达在45百万年前即已存在,首…     

嗅觉受体基因的研究进展

嗅觉在动物的生命活动中起着重要的作用, 与嗅觉相关的基因主要是嗅觉受体(Olfactory receptor, OR)基因。文章介绍了嗅觉受体基因的结构、表达调控、分布、分子进化及其多态性研究进展, 并讨论了该基因与嗅觉功能和嗅觉障碍的关系。     

基因组水平蝙蝠嗅觉受体基因的分子进化

翼手目动物（俗称蝙蝠）的食性分化显著,不同食性的蝙蝠具有显著不同的嗅球大小。为了研究嗅觉是否影响了蝙蝠食性的进化,我们利用网上已公布的10种蝙蝠基因组的数据,通过同源比对的方法鉴定出所有的嗅觉受体基因,并进行嗅觉受体基因亚家族的分类,进而比较嗅觉受体基因亚家族的数目差异。结果显示,蝙蝠的嗅觉受体基因与其它哺乳动物一样,都可以分为13个单系起源的亚家族;在Yinpterochiroptera亚目中,OR1/3/7、OR2/13、OR5/8/9等3个嗅觉受体亚家族在食果蝙蝠中均发生了不同程度的扩张,基因数目显著地多于食虫蝙蝠,提示嗅觉在食果蝙蝠取食过程中具有重要的作用。因此,本研究在基因组水平上重现了蝙蝠嗅觉受体基因的进化历史,揭示了3个嗅觉受体基因亚家族的功能可能与食果蝙蝠的食性相关,突出了嗅觉对动物食性的重要作用.     

2004年度诺贝尔生理学和医学奖简介

2004年诺贝尔生理学和医学奖颁发给两位美国科学家理查德·阿克塞尔(Richard Axel)和琳达·巴克(Linda Buck).他们发现嗅觉系统中一个大家族基因,这一大家族基因可以表达等量的嗅觉受体类型.这些受体位于鼻腔上皮的嗅觉神经元上,以检测不同的气味分子.     

脊索动物嗅觉受体基因命名法的发展

嗅觉受体属于G蛋白偶联受体家族,在脊索动物的整个生命周期中都扮演着至关重要的角色。与其他多数基因家族不同,嗅觉受体家族是一个成员数量庞大的超基因家族,为它们合乎逻辑的命名可以更好地对该家族进行描述、分析和讨论,也可以为机器学习程序从庞大的嗅觉受体数据库自动构建相应的蛋白结构和功能知识库提供语义信息。由于脊索动物嗅觉受体演化速度很快、基因数量庞大、假基因比率高、在物种及染色体上分布差异巨大等多方面的原因,给嗅觉受体基因合理的命名较为困难。三十多年来,伴随着嗅觉受体研究领域的发展,嗅觉受体基因命名法也经历了多次迭代,在每个阶段都发挥着积极的作用。随着测序技术和生物信息学算法工具的发展,随之而来的是新注释的海量的嗅觉受体基因,这使已有的嗅觉受体基因命名法变得越来越难以适应大数据挖掘和知识工程的系统开发,因此迫切需要一个能满足当下需求的嗅觉受体基因命名法。     

嗅球对嗅觉信息的处理

哺乳动物的嗅觉系统拥有惊人的能力,它可以识别和分辨成千上万种分子结构各异的气味分子。这种识别能力是由基因决定的。近年来,分子生物学和神经生理学的研究使得我们对嗅觉识别的分子基础和嗅觉系统神经连接的认识有了质的飞跃。气味分子的识别是由一千多种气味受体完成的,鼻腔中的嗅觉感觉神经元表达这些气味受体基因。每个感觉神经元只表达一种气味受体基因。表达同种气味受体的感觉神经元投射到嗅球表面的一个或几个嗅小球中,从而在嗅球中形成一个精确的二维连接图谱。了解嗅球对气味信息的加工和处理方式是我们研究嗅觉系统信号编码的一个重要环节。文章概述并总结了有关嗅球信号处理的最新研究成果。     

科学家破译蜜蜂全基因组揭秘蜜蜂祖籍在非洲

新华社电一个跨国科学家团队2006年10月26日宣布完成蜜蜂的基因组测序工作。他们发现这种昆虫实际上源于非洲,后来经过2次迁徙才“移民”到欧洲。此外,这项研究成果还意味着科学家有可能从基因层面揭开蜜蜂的复杂社会习性和敏锐嗅觉之谜。     

海洋哺乳动物信息素嗅觉的分子进化

研究感觉基因的进化规律是动物进化领域长期探索的重要问题.哺乳动物通常具有2套嗅觉系统:主要嗅觉系统(MOS)和犁鼻器系统(VNS).其中,VNS主要感知动物个体释放的信息素分子,而信息素在动物的生殖和社会行为中起重要调节作用.为了研究动物信息素嗅觉进化的背后推动力,对海洋哺乳动物的代表物种进行了Trpc2基因(VNS功能的分子标记)的序列测定和进化分析.以前的研究表明,Trpc2基因仅在VNS中表达,其序列完整/缺失与VNS的功能完整/退化完全一致.本研究结果显示,鲸类和海牛类的Trpc2为假基因,鳍脚类的1个分支类群(海豹类)和水獭类的Trpc2也是假基因,提示VNS功能丢失,即信息素嗅觉功能退化;而北极熊和鳍脚类的另一个分支类群(海狮类)保留了1个完整的Trpc2,并且这个基因仍受强烈的净化选择和功能限制,提示信息素嗅觉功能仍然保留.进一步分析表明,信息素嗅觉退化的海兽主要在水中交配,而信息素嗅觉保留的海兽主要在陆地上交配.本研究提出了一个新的科学假说:交配场所的选择可能推动了海洋哺乳动物信息素嗅觉的进化.     

七星瓢虫触角转录组及嗅觉相关基因分析

【目的】瓢虫科食性高度分化。本研究旨在通过建立七星瓢虫Coccinella septempunctata触角转录组数据库,探讨其触角嗅觉相关基因与食性分化的关系。【方法】采用Illumina HiSeq 4000高通量测序平台对七星瓢虫成虫触角转录组进行测序、组装、注释,挖掘嗅觉相关基因,并与已发表的茄二十八星瓢虫Henosepilachna viginyioctopunctata转录组进行比较。【结果】共获得七星瓢虫触角转录组31 775条unigenes,其中69.71%的序列得以注释,NR数据库中注释最多,为20 539条。据注释信息,挖掘到27个嗅觉相关基因,包括1个气味结合蛋白(odorant binding protein, OBP)基因,13个化学感受蛋白(chemosensory protein, CSP)基因,4个气味受体(odorant receptor, OR)基因,7个味觉受体(gustatory receptor, GR)基因和2个感觉神经元膜蛋白(sensory neuron membrane protein, SNMP)基因。相对应地,在植食性茄二十八星瓢虫转录组中鉴定到38个嗅觉相关基因,包括七星瓢虫中未发现的1个离子型受体(ionotropic receptor, IR)基因。在各类型嗅觉相关基因中,茄二十八星瓢虫转录组的OBP基因比例(13.16%)高于七星瓢虫触角转录组的(3.70%),而七星瓢虫触角转录组的GR基因比例(25.93%)则高于茄二十八星瓢虫转录组的(13.16%)。【结论】触角嗅觉相关基因数目不是昆虫食性分化的主因。本研究获得了七星瓢虫触角转录组学资源,初步探讨了嗅觉相关基因同瓢虫食性分化的关系,为了解瓢虫乃至昆虫食性分化的分子基础提供了信息。     

Silence sets on a sensory map

Recent efforts to understand the contribution of neuronal activity in the creation of the olfactory sensory map have focused on odor-evoked events. In this issue of Neuron, Yu et al. discover a new role for neuronal activity in the organization and maintenance of the olfactory system. Their results highlight the role of spontaneous activity and synaptic transmission in axon outgrowth and olfactory neuron survival.     

Mitral cell differentiation and synaptogenesis of rat presumptive olfactory bulb in organ culture

Summary The ultrastructure of differentiating rat presumptive olfactory bulb in organ culture was investigated with particular reference to mitral cell differentiation and formation of synapses. The presumptive olfactory bulb and olfactory mucosa were dissected en bloc from rat embryos on the fifteenth day of gestation and cultured for 7 days, after which the expiants were examined by electron microscopy. The presumptive olfactory bulb had differentiated into a laminated structure with layers corresponding to the glomerular, external plexiform and mitral cell layers. Mitral-like cells were identified by their location and large cell size. Ultrastructural observations indicated that they were relatively well-differentiated. Their dendrites extended into the glomerular layer in which they were postsynaptic to incoming olfactory axons. The distal part of these dendrites frequently contained coated vesicles. Both asymmetrical and symmetrical synapses were found. The symmetrical synapses involved dendrodendritic contacts between periglomerular cells. Synapses in reciprocal arrangements were not observed in the organ cultures.     

Distribution of neuropeptides in the antennal lobes of male Spodoptera littoralis

Olfaction is an important sensory modality that regulates a plethora of behavioural expressions in insects. Processing of olfactory information takes place in the primary olfactory centres of the brain, namely the antennal lobes (ALs). Neuropeptides have been shown to be present in the olfactory system of various insect species. In the present study, we analyse the distribution of tachykinin, FMRFamide-related peptides, allatotropin, allatostatin, myoinhibitory peptides and SIFamide in the AL of the male Egyptian cotton leafworm, Spodoptera littoralis. Immunocytochemical analyses revealed that most neuropeptides were expressed in different subpopulations of AL neurons. Their arborisation patterns within the AL suggest a significant role of neuropeptide signalling in the modulation of AL processing. In addition to local interneurons, our analysis also revealed a diversity of extrinsic peptidergic neurons that connected the antennal lobe with other brain centres. Their distributions suggest that extrinsic neurons perform various types of context-related modulation.     

The morphology and ultrastructure of the peripheral olfactory organ in newly metamorphosed coral-dwelling gobies, Paragobiodon xanthosomus Bleeker (Gobiidae, Teleostei)

We examined the peripheral olfactory organ in newly metamorphosed coral-dwelling gobies, Paragobiodon xanthosomus (SL=5.8mm+/-0.8mm, N=15), by the aid of electron microscopy (scanning and transmission) and light microscopy. Two bilateral olfactory placodes were present in each fish. They were oval-shaped and located medio-ventrally, one in each of the olfactory chambers. Each placode had a continuous cover of cilia. The placode epithelium contained three different types of olfactory receptor neurons: ciliated, microvillous and crypt cells. The latter type was rare. Following a pelagic larval phase, P. xanthosomus settle to the reef and form an obligate association with one species of coral, Seriatopora hystrix. Their well-developed olfactory organs likely enable larvae of P. xanthosomus to detect chemical cues that assist in navigating towards and selecting appropriate coral habitat at settlement. Our findings support past studies showing that the peripheral olfactory organ develops early in coral reef fishes.     

Induced and constitutive heat shock protein expression in the olfactory system—A review, new findings, and some perspectives

Heat shock, or stress, proteins (HSPs) are cellular proteins induced in response to conditions that cause protein denaturation, and their induction is essential for survival of such conditions. In the olfactory system we have found intense HSP expression occurs during normal processing of environmental odorants/inhalants as well as following hyperthermia and drug exposure. The HSPs involved include ubiquitin, HSP70, HSC70, and HSP25. Responses are both cell type- and stress-specific, occurring primarily in olfactory supporting cells and to some extent in Bowman’s gland acinar cells. Responses to these stresses are not seen in olfactory sensory neurons. This article reviews those studies and the significance of their findings. It also discusses a distinct subpopulation of rat olfactory sensory neurons (OSNs), the 2A4(+)OSNs, found to be constitutively reactive with HSP70, the predominantly stress-inducible isoform of the 70 kD HSP family. Their high HSP70 expression appears to confer on the 2A4(+)OSNs an enhanced ability to survive damage-induced OSN turnover. New findings are also presented on HSP25-specific changes following olfactory bulbectomy. All data are discussed in the context of the overall olfactory and bioprotective functions of the olfactory mucosa.     

Organization of the olfactory system of the Indian major carp <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.): A scanning and transmission electron microscopy study

Catla catla, Labeo rohita, and Cirrhinus mrigala represent important alimentary fish in India. Their reproduction/breeding depends on seasons. Fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in central regulation of reproduction. However, no electron microscopy data are available on organization of olfactory components of these fish. We studied organization of the olfactory organ in male L. rohita using scanning (SEM) and transmission electron microscopy (TEM). This organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The olfactory organ is ovoid in shape and consists of about 47–52 lamellae in adults and about 14–20 lamellae in fingerlings. These lamellae originate from the midline raphe. By SEM, microvillar sensory and ciliated non-sensory cells were observed in the lamellae. TEM revealed microvillar receptor cell with rough endoplasmic reticulum and Golgi apparatus towards apical end. Basal cells were present at the base of receptor cell, supporting cells were located adjacent to the olfactory receptor neurons, while epithelial cells—in the nonsensory part of olfactory epithelium. Mast, blastema, and macrophage cells were also found at the basement membrane. This work is the first publication on ultrastructural organization of the olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of the olfactory system and opens new avenues for further investigation of chemical neuroanatomy, sensory signal processing, and neural regulation of reproduction in the Indian major carp.     

Organization of olfactory system of the Indian major carp Labeo rohita (Ham.): a study using scanning and transmission microscopy

Catla catla, Labeo rohita, and Cirrhinus mrigala are important alimentary fish in India. Their reproduction (breeding) depends on season. The fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in the central regulation of reproduction. However, in the available literature, any electron microscopy data on organization of olfactory elements in these fish are absent. We have studied ultrastructure of the olfactory organ in male L. rohita by using scanning (SEM) and transmission electron microscopy (TEM). The olfactory organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The organ has oval shape and consists of approximately 47-52 lamellae in adult fish and of 14-20 lamellae in fish at the stage of fingerling. These lamellae originate from the midline raphe. By using SEM, the presence of microvillar sensory and ciliated non-sensory cells in these lamellae is shown. By using TEM, a microvillar receptor cell is revealed, which has rough endoplasmic reticulum and Golgi apparatus towards the apical end. Basal cells are found at the base of the receptor cell; supporting cells are located adjacent to olfactory receptor neurons, while epithelial cells--in the non-sensory part of olfactory epithelium. Mast, blastema and macrophages cells are also found in the basal lamina. This work is the first publication on structural organization of olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of olfactory system and opens new opportunities for study of chemical neuroanatomy, sensory signal processing, and nervous regulation of reproduction of the Indian major carp.     

Enhancement of odorant detection sensitivity by the expression of odorant-binding protein

Odorant-binding proteins are low molecular weight, soluble proteins that are secreted by glands of the nasal cavity. Their function is known to be the transport of hydrophobic odorants. This feature is important to artificial olfactory biosensors, which operate in the aqueous phase. In this study, one of rat odorant-binding proteins, OBP3, was inserted into a mammalian expression vector pcDNA3, expressed, and secreted from human embryonic kidney-293 (HEK-293) cells. The his(6) tag and signal peptide of the prelysozyme (plys) were fused with OBP3 for the detection and secretion of the proteins, respectively. The secretion level of OBP3 was maximal at 3h of incubation time. The secreted OBP3 increased the solubility of a hydrophobic odorant, octanal, which is the specific odorant of rat olfactory receptor I7. The secreted OBP3 also bound to olfactory receptor I7. These interactions consequently increased the cellular signal intensity stimulated by the odorant in the cells expressing olfactory receptor I7. Our findings indicate that odorant-binding protein can be effectively used to increase the sensitivity of olfactory receptor-based biosensors.     

Changes in distribution and abundance of antennal sensilla during growth of Locusta migratoria L. (Orthoptera : Acrididae)

The antenna of Locusta migratoria (Orthoptera : Acrididae) increases in length by the production of new annuli proximally and by elongation of existing annuli. The most distal annuli are fully differentiated at the time of hatching and no new olfactory sensilla are added to them at subsequent molts. More proximally, the differentiation of trichoid contact chemoreceptors precedes the development of olfactory sensilla. Sensillum differentiation proceeds from distal to proximal along the antenna and more distal annuli attain full development at each molt. The biggest increase in numbers of olfactory sensilla occurs at the final molt. On any one annulus, most olfactory sensilla are restricted to sensory fields on the anterior and posterior faces. Their spacing within these fields is consistent with the existence of separate but interacting chaetogens regulating the differentiation of basiconic and coeloconic sensilla.     

Experimental study of early olfactory neuron differentiation and nerve formation using quail-chick chimeras

For the formation of a functional olfactory system, the key processes are neuronal differentiation, including the expression of one or the other olfactory receptors, the correct formation of the nerve and organization of periphero-central connections. These processes take place during embryonic development starting from early stages. Consequently, avian embryos afford an attractive model to study these mechanisms. Taking advantage of species-specific equipment of olfactory receptors genes in different bird species, interspecific avian chimeras were set up by grafting early chick olfactory placodes in same stage quail embryos. Their analysis was performed using different complementary approaches. In situ hybridisation using probes to different chick olfactory receptor (COR) genes indicated that the choice of expression of an olfactory receptor by a neuron is independent of the environment of the olfactory placode and of interactions with the central nervous system. Futhermore, a chick olfactory receptor gene subgroup (COR3 ), absent in the host genome, was expressed by neurons from the graft. The question was then raised of the consequences of such heterospecific differentiation on axonal projections and fiber convergence. The DiI labeling of olfactory fibres in chimeras revealed anomalies in the formation of the nerve from the chick graft. In agreement with the hypothesis of olfactory receptor (OR) involvement in axonal guidance and periphero-central synapse organisation, the presence of migrating cells and axonal fibres from the graft, expressing foreign ORs and having different interactions with the host environment than the host fibres and migrating cells, might explain these anomalies.