Colonialism and ethnicity: A theory and comparative case study

This article explores Arab American "invisibility" as a central theme in the historical narrative of Arab immigrants and their descendants in North America. "Invisibility" is primarily addressed in terms of Arab Americans' paradoxical positioning within the US racial/ethnic classification system. The article argues that four central paradoxes shape Arab American identity. The first paradox is that Arab Americans are a complex, diverse community, but are represented as a monolith in popular North American media images. The second paradox is that Arab Americans are simultaneously racialized as whites and as non-whites. The third paradox is that Arab Americans are racialized according to religion (Islam) rather than biology (phenotype). The fourth paradox involves the intersection between religious forms of identity that Arab immigrants bring to the US and racial forms of identity that structure US society. Overall, the article claims that each paradox of Arab American identity reinforces the difficulties associated in classifying this population.     

拟南芥矮小丛生突变体的分离与分子鉴定

顶端优势是指侧生分生组织的生长被主茎或主花序所抑制.最近的研究通过分离和鉴定顶端优势发生改变的突变体开始揭示顶端优势的分子机制.通过T-DNA标签法分离了拟南芥矮小丛生(bushy and dwarf 1, bud1 )突变体.突变体植株的表型包括顶端优势丧失、株型矮小,表明bud1 突变体存在生长素代谢、运输或信号传导的缺陷.一个对生长素特异反应的启动子驱动的报告基因在bud1 中表达模式改变.生长素敏感性和运输能力的测定表明这两个过程在 bud1中均正常.以上结果显示bud1 表型是生长素代谢缺陷的结果.遗传分析表明BUD1 为半显性突变且与一个T-DNA插入共分离,可通过iPCR方法分离.     

拟南芥矮小丛生突变体的分离与分子鉴定

顶端优势是指侧生分生组织的生长被主茎或主花序所抑制。最近的研究通过分离和鉴定顶端优势发生改变的突变体开始揭示顶端优势的分子机制。通过T-DNA标签法分离了拟南芥矮小丛生(bushy and dwarf l,budl)突变体。突变体植株的表型包括顶端优势丧失、株型矮小,表明budl突变体存在生长素代谢、运输或信号传导的缺陷。一个对生长素特异反应的启动子驱动的报告基因在budl中表达模式改变。生长素敏感性和运输能力的测定表明这两个过程在budl中均正常。以上结果显示budl表型是生长素代谢缺陷的结果。遗传分析表明BUDI为半显性突变且与一个T-DNA插入共分离,可通过iPCR方法分离。     

Geminivirus classification and nomenclature: progress and problems

During the last few years there has been some confusion among geminivirologists about how to determine the taxonomic status of a geminivirus and provide appropriate names for newly discovered viruses. The Seventh Report of the International Committee on Taxonomy of Viruses (ICTV) published in 2000, that provides guidelines for classification within the family Geminiviridae, is rapidly becoming obsolete, due mainly to the large number of complete genomic sequences that have become available. These sequences have provided a wealth of information with which to establish a coherent and durable taxonomic system, although the realisation that frequent inter‐species recombination events occur has introduced an additional level of complexity. This has resulted in a number of individual initiatives that were not fully compatible with current classification. The Geminiviridae Study Group of the ICTV exploited the last two International Geminivirus Workshops, held in Puerto Rico (1998) and Norwich, UK (2001), to debate some of the issues arising, allowing taxonomic proposals to be formulated that are in the process of being accepted by the ICTV for publication in the Eighth Report due in 2004. The present paper reviews these established principles and provides a reference with which to name and classify geminiviruses appropriately.     

insomniac and Cullin-3 regulate sleep and wakefulness in Drosophila

In a forward genetic screen in Drosophila, we have isolated insomniac, a mutant that severely reduces the duration and consolidation of sleep. Anatomically?restricted genetic manipulations indicate that insomniac functions within neurons to regulate sleep. insomniac expression does not oscillate in a circadian manner, and conversely, the circadian clock is intact in insomniac mutants, suggesting that insomniac regulates sleep by pathways distinct from the circadian clock. The protein encoded by insomniac is a member of the BTB/POZ superfamily, which includes many proteins that function as adaptors for the Cullin-3 (Cul3) ubiquitin ligase complex. We show that Insomniac can physically associate with Cul3, and that reduction of Cul3 activity in neurons recapitulates the insomniac phenotype. The extensive evolutionary conservation of insomniac and Cul3 suggests that protein degradation pathways may have a general role in governing the sleep and wakefulness of animals.     

Development of tRNA synthetases and connection to genetic code and disease

The genetic code is established by the aminoacylation reactions of aminoacyl tRNA synthetases, where amino acids are matched with triplet anticodons imbedded in the cognate tRNAs. The code established in this way is so robust that it gave birth to the entire tree of life. The tRNA synthetases are organized into two classes, based on their active site architectures. The details of this organization, and other considerations, suggest how the synthetases evolved by gene duplications, and how early proteins may have been statistical in nature, that is, products of a primitive code where one of several similar amino acids was used at a specific position in a polypeptide. The emergence of polypeptides with unique, defined sequences--true chemical entities--required extraordinary specificity of the aminoacylation reaction. This high specificity was achieved by editing activities that clear errors of aminoacylation and thereby prevent mistranslation. Defects in editing activities can be lethal and lead to pathologies in mammalian cells in culture. Even a mild defect in editing is casually associated with neurological disease in the mouse. Defects in editing are also mutagenic in an aging organism and suggest how mistranslation can lead to mutations that are fixed in the genome. Thus, clearance of mischarged tRNAs by the editing activities of tRNA synthetases was essential for development of the tree of life and has a role in the etiology of diseases that is just now being understood.     

Shell shape and land-snail habitat in a Mediterranean and desert fauna

The bimodal distribution of shell shape (height: diameter), that is found in various geographically widely separate and taxonomically distinct land snail faunas of many different regions of the world, occurs also in a Mediterranean fauna and in a desert fauna that is derived from it. The desert fauna is, however, closer to the bisector than the Mediterranean one. High-spired snails are mainly rock-dwellers, and equidimensional to low-spired snails are bush-dwellers or soil-diggers, with a few rock-dwellers; litter-dwellers are small-sized species that may have either high- or low-spired shells. These results are discussed in adaptive terms. Litter is probably the more primitive of these micro-environments. Many of the small, litter-dwelling snails are ovo-viviparous rather than oviparous, perhaps so as to avoid attacks on the eggs by saprophytic fungi. The shift away from the litter environment is accompanied by a trend to abandon the ovo-viviparous strategy, in favour of oviparity, the snail using its foot to dig into the soil and lay eggs. The conchometric differences between bush-, ground- and rock-dwelling snails may perhaps reflect selective pressure to increase the size of the foot; and constraints of a habitat that consists of narrow interspaces between rocky boulders. Snails that habitually dig into the ground during periods of inactivity, and roam over the ground when active, requires a very large foot and, consequently, a very large-mouthed shell to accommodate it; the result is an equidimensional shell, globose or turbiniform in shape. Snails that climb up vertical vegetation would also require a large foot, and consequently a large-mouthed shell to contain it. A fully globose shell would however be disadvantageous, since it might cause undesired torque. Hence, bush-dwellers tend to be flatter than soil-diggers. Snails that habitually live in rock crevices, and on hard substrata, would not require a very large foot; they would need a narrow shell, both to enable easy manoeuvring through crevices and to reduce torque, the result being a small-mouthed, usually high-spired shell. The classification of land snails into bush-, soil- or rock-dwellers closely follows the taxonomic classification. In those species that depart from the habitat that is typical of their taxonomic group towards another habitat, the shell alters its shape accordingly.     

Morphological variation between lake- and stream-dwelling rock bass and pumpkinseed populations

Pumpkinseed Lepomis gibbosus and rock bass Ambloplites rupestris stream populations of both sexes were significantly different in external morphology from lake populations in a central Ontario, Canada, watershed. The predictions that stream fishes would be more slender-bodied, and have a more anterior placement of lateral fins than lake fishes were generally supported. The prediction that stream fishes would have a more robust caudal peduncle was partially supported. The prediction that fin size would be larger in stream fishes was not supported, as lake rock bass generally had longer and wider fins than those from stream sites. The results suggest that in some species, smaller fins may be favoured in stream-dwelling individuals because the reduction of drag during swimming more than compensates for their reduced power and propulsion efficiency in a current. Smaller fin size in stream-dwelling centrarchids may be related to their body shape, or to their low usage of fast-moving water within the streams they inhabit.     

Characterization and localization of dynein and myosins V and VI in the ovaries of queen bees

The presence of myosin and dynein in the ovaries of both Apis mellifera and Scaptotrigona postica was investigated in extracts and in histological sections. In the ovary extracts, motor proteins, myosins V, VI and dynein were detected by Western blot. In histological sections, they were detected by immunocytochemistry, using a mouse monoclonal antibody against the intermediary chain of dynein and a rabbit polyclonal antibody against the myosin V head domain. The myosin VI tail domain was recognized by a pig polyclonal antibody. The results show that these molecular motors are expressed in the ovaries of both bee species with few differences in location and intensity, in regions where movement of substances is expected during oogenesis. The fact that antibodies against vertebrate proteins recognize proteins of bee species indicates that the specific epitopes are evolutionarily well preserved.     

Placental mosaicism and intrauterine survival of trisomies 13 and 18.

Cytogenetic analysis of 14 placentas from live newborn infants or from terminated pregnancies with trisomies 13 and 18 revealed that all were mosaic. The mosaicism was confined to the cytotrophoblast and not detected in villous stroma, chorionic plate, or amnion. The percentage of cells with a normal karyotype varied from 12% to 100%, the average being 70%. No such confined mosaicism could be detected in 12 placentas of trisomy 21 fetuses. These findings suggest that a postzygotic loss of a trisomic chromosome in a progenitor cell of trophectoderm facilitates the intrauterine survival of trisomy-13 and -18 conceptuses. They also imply that it is placental function which determines the intrauterine survival and that the mother plays no active role in rejection of trisomic conceptions. The combination of both a pre- and post-zygotic cell division defect in viable trisomy-13 and -18 conceptions points to the possibility of a genetic predisposition to such events. The detection of only a diploid cell line in the cytotrophoblast of some pregnancies with trisomies 13 and 18 also suggests that direct preparation is unreliable for prenatal diagnosis of these trisomies on chorionic villi sampling and that long-term villous culture should be used.     

Marine biogeography and ecology: invasions and introductions

Although biogeography and ecology had previously been considered distinct disciplines, this outlook began to change in the early 1990s. Several people expressed interest in creating a link that would help ecologists become more aware of external influences on communities and help biogeographers realize that distribution patterns had their genesis at the community level. They proposed an interdisciplinary approach called macroecology. This concept has been aided by the advent of phylogeography, for a better knowledge of genetic relationships has had great interdisciplinary value. Two areas of research that should obviously benefit from a macroecological approach are: (1) the question of local vs. regional diversity and (2) the question of whether invader species pose a threat to biodiversity. The two questions are related, because both deal with the vulnerability of ecosystems to penetration by invading species. Biogeographers, who have studied the broad oceanic patterns of dispersal and colonization, tend to regard isolated communities as being open to invasion from areas with greater biodiversity. It became evident that many wide‐ranging species were produced in centres of origin, and that the location of communities with respect to such centres had a direct effect on the level of species diversity. Ecologists, in earlier years, thought that a community could become saturated with species and would thereafter be self‐sustaining. But recent research has shown that saturation is probably never achieved and that the assembly of communities and their maintenance is more or less dependent on the invasion of species from elsewhere. The study of invasions that take place in coastal areas, usually the result of ship traffic and/or aquaculture imports, has special importance due to numerous opinions expressed by scientists and policy‐makers that such invasions are a major threat to biodiversity. However, none of the studies so far conducted has identified the extinction of a single, native marine species due to the influence of an exotic invader. Furthermore, fossil evidence of historical invasions does not indicate that invasive species have caused native extinctions or reductions in biodiversity.     

Construction and analysis of parallel and antiparallel Holliday junctions

The Holliday junction is a four-stranded DNA intermediate that arises during recombination reactions. We have designed and constructed a set of Holliday junction analogs that model each of the ideal conformations available to a 2-fold symmetric four-arm junction. The strategy used is to connect two arms of a junction molecule with a short tether of thymidines. These DNA molecules share a common core sequence but have different arms that are connected so that each molecule is constrained in either an antiparallel or a parallel structure. For tethered antiparallel molecules the identity of the crossover strands is determined by which arms are connected. Different arm connections gave molecules representing each of the two antiparallel crossover isomers. Two parallel molecules that differ in the length and position of the tether exhibit opposite biases in their choice of crossover strands. Thus, a physical constraint applied at a distance from the branch point can determine the conformation of a junction.     

Rest length and compliance of non-immobilised and immobilised rabbit soleus muscle and tendon

The first aim of this study was to measure the contributions of muscle and tendon to the total compliance of resting muscle-tendon units. A second aim was to determine whether the decrease in muscle-tendon unit rest length produced by prolonged immobilisation in a shortened position is mediated primarily by adaptations of the muscle or tendon. One ankle joint from each of five rabbits was immobilised in a plantarflexed position for 14 days. The passive length-tension properties of soleus muscle fascicles and tendons from both hindlimbs were measured using a video-based tensile-testing system. In non-immobilised muscles, muscle fascicle strains exceeded tendon strains by up to four times. However, because the rest length of tendon was much greater than that of muscle fascicles, changes in tendon length accounted for nearly half of the total change in muscle-tendon unit length. The rest length of immobilised muscle-tendon units was less than that of non-immobilised muscle-tendon units from contralateral limbs. Most of this difference was attributable to a change in the rest length of the tendon; there was little change in the rest length of muscle fascicles. It is concluded that the tendon is responsible for a large part of the compliance of rabbit soleus muscle-tendon units at physiological resting tensions, and that adaptation of tendon rest length is the primary mechanism by which the rabbit soleus shortens in response to immobilisation at short lengths. Accepted: 7 May 1997     

CFTR and TNR-CFTR expression and function in the kidney

The cystic fibrosis transmembrane conductance regulator (CFTR) is abundantly expressed in the kidney. CFTR mRNA is detected in all nephron segments of rats and humans and its expression is higher in the renal cortex and outer medulla than in the inner medulla. CFTR protein is detected at the apical surface of both proximal and distal tubules of rat kidney but not in the outer medullary collecting ducts. The localization of CFTR in the proximal tubules is compatible with that of endosomes, suggesting that CFTR might regulate pH in endocytic vesicles by equilibrating H⁺ accumulation due to H⁺-ATPase activity. Many studies have also demonstrated that CFTR also regulates channel pore opening and the transport of sodium, chloride and potassium. The kidneys also express a CFTR splicing variant, called TNR-CFTR, in a tissue-specific manner, primarily in the renal medulla. This splicing variant conserves the functional characteristics of wild-type CFTR. The functional significance of TNR-CFTR remains to be elucidated, but our group proposes that TNR-CFTR may have a basic function in intracellular organelles, rather than in the plasma membrane. Also, this splicing variant is able to partially substitute CFTR functions in the renal medulla of Cftr^-/- mice and CF patients. In this review we discuss the major functions that have been proposed for CFTR and TNR-CFTR in the kidney.     

Capping and dynamic relation between domains 1 and 2 of gelsolin

Gelsolin is a protein that severs and caps actin filaments. The two activities are located in the N-terminal half of the gelsolin molecules. Severing and subsequent capping requires the binding of domains 2 and 3 (S2–3) to the side of the filaments to position the N-terminal domain 1 (S1) at the barbed end of actin (actin subdomains 1 and 3). The results provide a structural basis for the gelsolin capping mechanism. The effects of a synthetic peptide derived from the sequence of a binding site located in gelsolin S2 on actin properties have been studied. CD and IR spectra indicate that this peptide presented a secondary structure in solution which would be similar to that expected for the native full length gelsolin molecule. The binding of the synthetic peptide induces conformational changes in actin subdomain 1 and actin oligomerization. An increase in the polymerization rate was observed, which could be attributed to a nucleation kinetics effect. The combined effects of two gelsolin fragments, the synthetic peptide derived from an S2 sequence and the purified segment 1 (S1), were also investigated as a molecule model. The two fragments induced nucleation enhancement and inhibited actin depolymerization, two characteristic properties of capping. In conclusion, for the first time it is reported that the binding of a small synthetic fragment is sufficient to promote efficient capping by S1 at the barbed end of actin filaments. ©1998 European Peptide Society and John Wiley & Sons, Ltd.     

Native and activated properdin: interconvertibility and identity of amino- and carboxy-terminal sequences

The development of a two-step purification procedure of native properdin with good yield has allowed the physical and chemical comparison of native and activated properdin. The two forms of properdin have identical electrophoretic mobility, subunit size, and amino- as well as carboxyl-terminal amino acid sequences. The two forms of properdin can be interconverted by using mild denaturing agents, indicating that the change in biologic activity is conformational. Circular dichroism analysis of properdin reveals a significant variability in the tertiary structure. However, the differences are a result of the method of purification and do not correspond to the biologic activity of the protein, because the spectra of the interconverted forms of properdin do not change. This indicates that the conformational transition that causes biologic activity changes is small, relative to the conformational variations produced by other conditions that do not alter the biologic activity.     

Apoptosis and survival

The term apoptosis first appeared in the biomedical literature in 1972, to delineate a structurally distinctive mode of cell death responsible for cell loss within living tissues. The cardinal morphological features are cell shrinkage, accompanied by transient but violent bubbling and blebbing from the surface, and culminating in separation of the cell into a cluster of membrane-bounded bodies. Changes in several cell surface molecules also ensure that, in tissues, apoptotic cells are immediately recognised and phagocytosed by their neighbours. However, it is important to note that apoptosis is only one form of cell death and the particular death pathway that is the most important determinant for cancer therapy is not necessarily that which has the fastest kinetics, as is the bias in many laboratories, but rather that which displays the most sensitive dose-response relationship.     

杉木火力楠混交林养分归还与生产力

通过对野外试验和室内测试数据的整理分析．比较研究了杉木火力楠混交林和 杉木纯林养分归还、吸收等生态过程的特征以及生产力结果表明混交促进了养分归还过 程．可提高土壤肥力和系统生产力．１５年生混交林技和叶凋落物分别是纯林的２倍和３ 倍,其中容易分解的火力楠凋落物占 ６４％．混交林通过凋落物分解所归还的养分是纯林 的 ２～ ３倍．相当年凋落量 ６５． ９％的混交林根系年死亡量是纯林的 ２倍,在整个系统养分 归还中占有很大的份额．混交林土壤全 Ｎ、 ＮＨ＋４－Ｎ和有效 Ｋ分别比纯林提高 ６４． ３％。 ８２． ３ ％和 ６３． １％．与此同时土壤孔隙组成和水分过程也大为改善．混交林生产力较纯林 提高５２．７％．混交林５种大量元素的归还／吸收比率是纯林的２倍,表明混交林养分循环 效率较高,较少的人为维持可以保持较高的生产力水平．     

Stability and conformational dynamics of metallothioneins from the antarctic fish Notothenia coriiceps and mouse

The structural properties and the conformational dynamics of antarctic fish Notothenia coriiceps and mouse metallothioneins were studied by Fourier-transform infrared and fluorescence spectroscopy. Infrared data revealed that the secondary structure of the two metallothioneins is similar to that of other metallothioneins, most of which lack periodical secondary structure elements such as alpha-helices and beta-sheets. However, the infrared spectra of the N. coriiceps metallothionein indicated the presence of a band, which for its typical position in the spectrum and for its sensitivity to temperature was assigned to alpha-helices whose content resulted in 5% of the total secondary structure of the protein. The short alpha-helix found in N. coriiceps metallothionein showed an onset of denaturation at 30 degrees C and a T(m) at 48 degrees C. The data suggest that in N. coriiceps metallothionein a particular cysteine is involved in the alpha-helix and in the metal-thiolate complex. Moreover, infrared spectra revealed that both proteins investigated possess a structure largely accessible to the solvent. The time-resolved fluorescence data show that N. coriiceps metallothionein possesses a more flexible structure than mouse metallothionein. The spectroscopic data are discussed in terms of the biological function of the metallothioneins.