On the Distribution of the Crustacean Dorsal Organ

An oval, dorsal organ, variously bearing four minute pits around a central pore and/or encircled by a cuticular border, has been reported for the cephalic region of various groups of living and fossil crustaceans. Although varying somewhat in location and in size, the organ appears basically uniform in organization in at least two of the major crustacean taxa: Branchiopoda (especially Laevicaudata) and Malacostraca (Decapoda and Syncarida). Little is known about its ultrastructure and function in various groups, and it is likely that the term ‘dorsal organ’ also has been applied to several nonhomologous structures. In particular, the embryonic dorsal organ, reviewed recently by Fioroni (Fioroni, P. 1980.—Zoologische Jahrbücher (Anatomie) 104: 425–465) and apparently functioning in nutrition and ecdysis, is not the topic of this paper; that organ is similar in name and location only and appears in embryonic uniramians, chelicerates, and crustaceans. The function of the dorsal organ in branchiopods is in ion regulation, possibly a secondary modification of the original function in marine crustaceans, which is unknown. In larval decapods, the organ probably functions as a chemo- or mechano-receptor. We review the known occurrence of the crustacean dorsal organ, describe the similarities and differences in structure in various taxa, and review the competing hypotheses concerning its function. Phylogenetic implications are discussed.     

Regulation of Crustacean Molting: A Multi-Hormonal System

SYNOPSIS. In order to increase in size, arthropods must firstmolt (shed) their confining exoskeleton. This molting processis under the immediate control of the steroid molting hormone20-hydroxyecdysone (20-HE). Both the initial rise in circulatinghormone concentration and a coordinated decline are necessaryfor successful molting. Synthesis and/or release of ecdysone,the precursor to 20-HE, is regulated by the neuropeptide molt-inhibitinghormone (MIH). We have determined the primary amino acid sequenceof MIH in the lobster, Homarus americanus. This peptide hasa high degree of identity with the lobster hyperglycemic hormone.Another endocrine factor that appears to be involved in moltingis the juvenile hormone-like terpenoid methyl farnesoate (MF).We have characterized hemolymph MF binding proteins during themolt cycle. In addition, recent data indicate that MF may stimulatethe secretion of 20-HE in vivo and in vitro.     

Regulation of Release and Mode of Action of Crustacean Chromatophorotropins

Pigment movements in crustacean chromatophores are regulatedby pigment-concentrating and pigment-dispersing neurosecretoryhormones. The release of these hormones from the neurosecretorysystem is thought to be controlled by neural signals. Althoughthe exact cellular sources of chromatophorotropins and the natureof synaptic input to the neurosecretory system remain unresolved,recent pharmacological studies on fiddler crabs indicate thatcertain biogenic amines contribute to the release of some ofthe chromatophorotropins. The current evidence suggests that:5-hydroxytryptamine stimulates the release of RPDH (red pigmentdispersing hormone), dopamine triggers the release of RPCH (redpigment concentrating hormone), and norepinephrine stimulatesthe release of BPDH/MDH (black pigment/melanin dispersing hormone).Nothing is known of the regulation of release of leucophorotropinsand xanthophorotropins. Like most other peptide hormones, crustacean chromatophorotropinsare thought to exert their effect by first binding to receptorson the cell surface and then triggering a series of events leadingto cellular responses, but the details are far from clear. Recentwork suggests that hormone-induced pigment movements may bemodulated/mediated by alterations in cyclic nucleotide levelsand/or by changes in Ca²⁺ distribution or flux. Both cyclicnucleotides and Ca²⁺ may modulate motility by regulating theintegrity and/or function of cytoskeletal elements, but thedetails of this mechanism and the precise roles of cytoskeletalelements in the pigment-translocating process remain unresolved.     

The Sites of Action of Pericardial Organ Extract and 5-Hydroxytryptamine in the Decapod Crustacean Heart

Responses of isolated, perfused hearts of Homarm americanusto brief, internal application of extracts of pericardial organs(PO's) ofCancer borealis, or 5-hydroxytryptamine (5HT) are verysimilar over a thousand-told range of concentration: an increasein rate and amplitude of beating. These reach their maxima afterwashing out has begun, and recover within ten minutes. Externalapplication is ineffective and the substances do not interactwith effects of stretch stimulation. Intracellular recordingfrom heart muscle fibers reveals facilitation of depolarizationto bursts at heart beat frequencies. There may be some effectof 5HT directly on neuromuscular facilitation. Responses recordedfrom isolated cardiac ganglia show increased burst rate, burstduration, or both. Thresholds and the range of concentrationsfor which coordinated responses are recorded correspond to thosefor perfused hearts. It is concluded that the major sites ofaction of PO extract and 5HT are in the cardiac ganglion. 5HTtachyphlaxis and LSD block effects of 5HT, but not of PO extractor accelerator nerve stimulation. Intracellular recordings fromthe large ganglion cells show no effects on resting, synaptic,or spike potentials. Changes in membrane potential to currentpulses revealed no changes in membrane resistance or in theresistance of the electrotonic pathway between cells. Resultsof selective application to large or small cells suggested thatPO extract may contain a rate-increasing substance and one prolongingthe duration of bursts. The former, and 5HT, may influence pacemakerpotentials; the latter may increase the number of spikes a unitcan produce before becoming refractory.     

Regulation of Organ Growth by Morphogen Gradients

Morphogen gradients play a fundamental role in organ patterning and organ growth. Unlike their role in patterning, their function in regulating the growth and the size of organs is poorly understood. How and why do morphogen gradients exert their mitogenic effects to generate uniform proliferation in developing organs, and by what means can morphogens impinge on the final size of organs? The decapentaplegic (Dpp) gradient in the Drosophila wing imaginal disc has emerged as a suitable and established system to study organ growth. Here, we review models and recent findings that attempt to address how the Dpp morphogen contributes to uniform proliferation of cells, and how it may regulate the final size of wing discs.     

同源异型基因对花器官发育的调控

以ABC模型为基础,阐述了花器官发育调控的分子机制,对一些相关基因在其中的作用和研究进展作了介绍.     

Cyclin-CDK-CKI及UPP参与生殖调控及在甲壳动物性腺发育中的研究进展

Cyclin-CDK-CKI是参与真核细胞周期调控的3个重要的调节因子。泛素蛋白酶体途径(ubiquitin proteasome pathway,UPP)是真核细胞内非溶酶体途径的蛋白质选择性降解的重要途径。细胞周期中许多时相特异性周期蛋白通过泛素化被周期性的降解对于细胞分裂的调控进程具有重要的作用。主要综述了Cyclin-CDK-CKI和UPP的组成、生理生化特性及其参与生殖调控的作用机制,同时阐述了这两大系统之间的联系及其在甲壳动物性腺发育中的研究进展。     

Proteins of the Crustacean Exoskeleton

We describe here some of the components of the exoskeleton ofthe decapod crustacean with emphasis on the constituent proteins,including both structural and enzymatic. All four layers, butparticularly the inner three, of the exoskeletons of four brachyuranscontain high concentrations of proteins 31 kDa; the innermostmembranous layer is especially rich in such proteins. A numberof crab exoskeletal proteins resemble insect cuticle proteinsin size (M_r) and isoelectric point (pI). A further similarityis the cross reactivity of crab exoskeletal proteins with fourdifferent antibodies against cuticular proteins of two speciesof insects. One of the small M_r exoskeletal proteins in theBermuda land crab Gecarcinus lateralis has a similar distributionas a protein of similar size in the cuticle of the tobacco hornworm Manduca sexta. The partial dissolution of an old exoskeletonand formation of the two outer layers of a new exoskeleton aremajor events in readying a crustacean for the increase in sizethat occurs at each molt. Expressing both parallel and sequentialactivation of a number of genes, a single layer of epidermalcells that bounds a crustacean such as G. lateralis synthesizesspecific proteins at different stages of the intermolt cycleas the outermost epicuticle and exocuticle are formed duringproecdysis and as the endocuticle and membranous layer are formedduring metecdysis. Finally, two sets of proteinases isolatedfrom integumentary tissues of land crabs degrade the same exoskeletalproteins in vitro as are degraded in vivo during proecdysis.     

器官发育和程序性细胞死亡中的基因调控——2002年诺贝尔生理学和医学奖工作介绍

2002年的诺贝尔生理学和医学奖授予了在器官发育和程序性细胞死亡研究领域中做出奠基性贡献的三位英美科学家．他们建立了线虫实验模型,完成了其细胞谱图的绘制,而且系统深入地研究了线虫的器官发育和程序性细胞死亡中的基因规则,并在高等哺乳动物中发现了相关的功能基因．这些研究对认识发育过程和揭示人类重大疾病的发病机理具有重要的理论价值和现实意义．     

中国明对虾大颚器的组织学及孕酮和雌二醇的检测

LeRoux于1968年首次描述了甲壳动物十足类的大颚器,并认为它与Y-器官是两个不同的腺体,Byard等在研究了美洲龙螯虾（Homarus americnus）大颚器的超微结构后指出,甲壳动物大颚器是类似于昆虫咽侧体的内分泌器官。Hinsch研究了蜘蛛蟹（Libinia emarginata）大颚器的结构和功能,指出该器官与甲壳动物的蜕皮和生殖均有密切联系。     

水稻花器官特征决定以及数量控制的分子机制

继双子叶模式植物拟南芥之后,单子叶模式植物水稻的生殖发育研究受到广泛的重视。随着水稻正向和反向遗传学研究的不断深入,人们发现了一些调控水稻花器官特征以及花器官数量的重要基因,使得对水稻花器官发育的调控机制有了更多的了解。本文着重概述和讨论水稻花器官特征决定以及花器官数量控制分子机理研究的最新进展。     

Phylogenetic implications of the Crustacean nauplius

The plesiomorphic mode of crustacean development is widely accepted to be via a larva called the nauplius. Extant taxa like the Cephalocarida, Branchiopoda, Ostracoda, Mystacocarida, Copepoda, Cirripedia, Ascothoracida, Facetotecta, Euphausiacea and Penaeidea hatch from an egg as a free-living nauplius. Other crustaceans show an embryonic phase of development suggestive of a naupliar organization. Several features of the nauplius larva have been proposed as diagnostic characters for the Crustacea: a median (nauplius) eye; at least three pairs of head appendages (antennules, antennae, mandibles); a posteriorly directed fold (the labrum) extending over the mouth and a cephalic (nauplius) shield. The relationship between trilobite protaspis with at least four appendages and the crustacean nauplius remains unclear, but reports of a copepod orthonauplius with four appendages are rejected. Swimming is suggested to represent the underived mode of locomotion for the crustacean nauplius, and that naupliar swimming directly results in naupliar feeding which also is underived.     

Crustacean Hyperglycemic Neuropeptides

The neurosecretory structures in the crustacean eyestalk areconsidered to be the source of factors regulating a considerablevariety of physiological processes. Although many hormonal "factors"have been postulated, only a few have been characterized indetail. Two pigmentary effector regulating neuropeptides havebeen completely characterized. A third substance, the hyperglycemichormone, has been isolated and characterized in terms of aminoacid composition. It is larger than the pigmentary effectorhormones (mol wt 6,000–7,000) and it is the first of theheretofore described invertebrate neurohormones that containsdisulfide bridges. Unlike the pigmentary effector hormones,the hyperglycemic neuropeptide exhibits species or systematicgroup specificity, recognizable by differences in amino acidcompositions and also expressed by lack of interspecific (orintergroup) biological activity. An antiserum permitted thedevelopment of a radioimmunoassay and immunocytochemical demonstrationof the hormone producing perikarya in decapods and in an isopod.Large immunopositive perikarya form a distinct group in themedulla terminalis ganglionic X-organ. This group sends a conspicuoustract of axons to the neurohemal organ, the sinus gland, wherethe hormone is stored in large quantities. It is believed tobe necessary for the regulation of resting levels of blood sugarand for elevation of blood sugar in situations of physiologicalneed. In general, however, the physiological mode of actionof the hormone is largely unknown.     

Crustacean Neuromuscular Mechanisms

Properties of crustacean muscle fibers and neuromuscular synapsesare discussed, with particular reference to the problems offast and slow contraction, synaptic diversity, and peripheralinhibition. Electrical and mechanical responses of crustacean muscle fibersare variable, and govern to a large extent the muscle's performance.Fast and slow contractions are often mediated by distinct "phasic"and "tonic" muscle fibers, as in abdominal muscles, in whichsuch fibers are segregated into two parallel sets of muscles.In leg muscles the fibers are often heterogeneous in propertiesand innervation. In doubly-motor-innervated muscles of crabsthe axons producing fast and slow contractions preferentiallyinnervate rapidly and slowly contracting fibers, respectively. Crustacean neuromuscular synapses vary greatly in electricalbehavior and in ultrastructural characteristics. Some motoraxons possess both facilitating and nonfacilitating synapses.The proportion of the different types of synapse associatedwith a motor axon probably determines in large measure the propertiesof the postsynaptic potentials evoked by that axon. Pre-synaptic and post-synaptic inhibition both occur, sometimesin the same muscle. The latter type is more common. Pre-synapticinhibition is thought to be mediated by the action of an inhibitorytransmitter-substance on receptors of the motor nerve terminals.     

Computerized Analysis of Crustacean Relationships

The strengths and weaknesses of phylogenetic analysis using computers are reviewed from the viewpoint of understanding crustacean evolution. Computerized methods require the explicit presentation of characters and character state homologies. New techniques allow investigators to design evolutionary models into a character data matrix, or to use evolutionary models that make minimal a priori assumptions. The computer analysis relieves the investigator from the highly repetitious testing of trees, allows the concentration on the character state data, and provides objective methods for comparing trees, primarily their length. These are regarded as the strengths of computerized methods. The weaknesses of these methods include the relatively inscrutable nature of the character data matrix compared with the overall ‘gestalt’ of resulting trees, the difficulties of defining discrete homologies within the Crustacea, especially for counts of segmentation, the lack of clear intermediate character states in some multistate segmental characters, and the inability to define evolutionary polarity. These difficulties may be overcome by analysing the data using the minimal assumption models of character evolution, and by a recognition that the trees are a result of the input data, and therefore the data should be criticized, rather than the trees themselves. A ‘consensus’ character data set, including most extant major groups of the Crustacea as well as several key fossils, was assembled and revised by the participants in the workshop. An artificial taxon, ‘ur-crustacean characters’, was introduced to root the tree. Three observations may be made from parsimony analyses using several weighting and tree rooting methods. (1) The currently accepted large scale phylogeny and classification of the Crustacea is not corroborated. (2) The number of supposed plesiomorphic traits possessed by a taxon is not a good index for early derivation in crustacean evolution. (3) The taxon Maxillopoda is not supported by the arrangement of any of the trees.     

植物器官大小相关基因研究进展

器官大小是植物形态的一个重要特征,而且具有严格的种属特异性。植物器官大小虽然受到外在的环境因素（如光照、营养等）的影响,但它由内在特有的细胞数目和细胞大小决定。许多通过转录调节、蛋白合成、激素调节或松弛细胞壁等途径作用于植物细胞繁殖和/或细胞扩张的基因已经被鉴定,它们的过表达或缺失表达能促进植物器官大小和加快植物生长。尽管如此,这些基因通过相对独立的途径起作用,在植物中难以阐明一个相对整合的器官大小基因调控网络,这也是该研究领域的亟待需要解决的问题。目前,一些器官大小相关基因已经应用农作物育种,并培育出显著增大的农作物品种,这也证实了利用器官大小基因进行植物品种选育的可行性。因此,通过研究药用植物器官大小的基因,人为地在分子水平上有目的的调控器官的大小和形态,是缓解当前许多药用植物面临的资源紧缺、枯竭濒危困境的可考虑途径之一。     

Radioimmunoassay and the Characterization of Crustacean Ecdysteroids

The development of the radioimmunoassay (RIA) for ecdysteroidshas permitted the sequential measurement of circulating ecdysteroidson individual organisms. In addition, used in conjunction withvarious chromatographic techniques, it has assisted in the identificationof ecdysteroids secreted by molting glands. The sensitivityof the assay has also permitted the monitoring of the rate ofsecretion of ecdysteroids by molting glands exposed to variousin vitro conditions. This latter approach will be of great utilityin determining the nature and effect of molt regulators (inhibitors)present in other tissues.