Vertebral Trabecular Bone Mechanical Properties Vary Among Functional Groups of Cetaceans.

Since their appearance in the fossil record 34 million years ago, modern cetaceans (dolphins, whales, and porpoises) have radiated into diverse habitats circumglobally, developing vast phenotypic variations among species. Traits such as skeletal morphology and ecologically linked behaviors denote swimming activity; trade-offs in flexibility and rigidity along the vertebral column determine patterns of caudal oscillation. Here, we categorized 10 species of cetaceans (families Delphinidae and Kogiidae; N = 21 animals) into functional groups based on vertebral centra morphology, swimming speeds, diving behavior, and inferred swimming patterns. We quantified trabecular bone mechanical properties (yield strength, apparent stiffness, and resilience) among functional groups and regions of the vertebral column (thoracic, lumbar, and caudal). We extracted 6 mm3 samples from vertebral bodies and tested them in compression in 3 orientations (rostrocaudal, dorsoventral, and mediolateral) at 2 mm min-1. Overall, bone from the pre-fluke/fluke boundary had the greatest yield strength and resilience, indicating that the greatest forces are translated to the tail during caudal oscillatory swimming. Group 1, composed of 5 shallow-diving delphinid species, had the greatest vertebral trabecular bone yield strength, apparent stiffness, and resilience of all functional groups. Conversely, Group 3, composed of 2 deep-diving kogiid species, had the least strong, stiff, and resilient bone, while Group 2 (3 deep-diving delphinid species) exhibited intermediate values. These data suggest that species that incorporate prolonged glides during deep descents in the water column actively swim less, and place relatively smaller loads on their vertebral columns, compared with species that execute shallower dives. We found that cetacean vertebral trabecular bone properties differed from the properties of terrestrial mammals; for every given bone strength, cetacean bone was less stiff by comparison. This relative lack of material rigidity within vertebral bone may be attributed to the non-weight-bearing locomotor modes of fully aquatic mammals.

Desde su aparición en el registro fósil 34 Mya, los cetáceos modernos (delfines, ballenas y marsopas) se han radiado a diversos hábitats a nivel mundial, desarrollando vastas variaciones fenotípicas entre especies. Rasgos como la morfología esquelética y los comportamientos vinculados ecológicamente denotan actividad de natación; las compensaciones en flexibilidad y rigidez a lo largo de la columna vertebral determinan los patrones de oscilación caudal. Aquí, categorizamos 10 especies de cetáceos (familias Delphinidae y Kogiidae; N = 21 animales) en grupos funcionales basados ​​en la morfología de los centros vertebrales, velocidades de nado, comportamiento de buceo y patrones de nado inferidos. Cuantificamos las propiedades mecánicas del hueso trabecular (límite elástico, rigidez aparente y resiliencia) entre grupos funcionales y regiones de la columna vertebral (torácica, lumbar y caudal). Extrajimos muestras de 6 mm3 de cuerpos vertebrales y las probamos en compresión en tres orientaciones (rostrocaudal, dorsoventral y mediolateral) a 2 mm min-1. En general, el hueso de la platija tuvo el mayor límite elástico y resiliencia, lo que indica que las mayores fuerzas se trasladan a la cola durante la natación oscilatoria caudal. El grupo 1, compuesto por cinco especies de delfínidos de buceo superficial, tuvo el mayor límite elástico del hueso trabecular vertebral, rigidez aparente y resiliencia de todos los grupos funcionales. Por el contrario, el Grupo 3, compuesto por dos especies de kogiidos de inmersión profunda, tenía el hueso menos fuerte, rígido y resistente, mientras que el Grupo 2 (tres especies de delfínidos de inmersión profunda) exhibió valores intermedios. Estos datos sugieren que las especies que incorporan deslizamientos prolongados durante descensos profundos en la columna de agua nadan menos activamente y colocan cargas relativamente más pequeñas en sus columnas vertebrales, en comparación con las especies que realizan inmersiones menos profundas. Encontramos que las propiedades del hueso trabecular vertebral de los cetáceos diferían de las propiedades de los mamíferos terrestres; por cada resistencia ósea dada, el hueso de cetáceo era menos rígido en comparación. Esta relativa falta de rigidez del material dentro del hueso vertebral puede atribuirse a los modos locomotores que no soportan peso de los mamíferos totalmente acuáticos.

Predator-Prey Interactions Examined Using Lionfish Spine Puncture Performance.

Puncture mechanics can be studied in the context of predator-prey interactions and provide bioinspiration for puncture tools and puncture-resistant materials. Lionfish have a passive puncture system where venomous spines (dorsal, anal, and pelvic), the tool, may embed into a predator's skin, the target material, during an encounter. To examine predator-prey interactions, we quantified the puncture performance of red lionfish, Pterois volitans, spines in buccal skin from two potential predators and porcine skin, a biological model for human skin. We punctured dorsal, anal, and pelvic lionfish spines into three regions of buccal skin from the black grouper (Mycteroperca bonaci) and the blacktip shark (Carcharhinus limbatus), and we examined spine macro-damage (visible without a microscope) post puncture. Lionfish spines were more effective, based on lower forces measured and less damage incurred, at puncturing buccal skin of groupers compared to sharks. Anal and dorsal spines incurred the most macro-damage during successful fish skin puncture trials, while pelvic spines did not incur any macro-damage. Lionfish spines were not damaged during porcine skin testing. Anal spines required the highest forces, while pelvic spines required intermediate forces to puncture fish skin. Dorsal spines required the lowest forces to puncture fish skins, but often incurred macro-damage of bent tips. All spine regions required similar forces to puncture porcine skin. These data suggest that lionfish spines may be more effective at puncturing humans such as divers than potential fish predators. These results emphasize that puncture performance is ultimately determined by both the puncture tool and target material choice. Lionfish puncture performance varies among spine region, when taking into account both the puncture force and damage sustained by the spine.

Body and Pectoral Fin Kinematics During Routine Yaw Turning in Bonnethead Sharks (Sphyrna tiburo).

Maneuvering is a crucial locomotor strategy among aquatic vertebrates, common in routine swimming, feeding, and escape responses. Combinations of whole body and fin movements generate an imbalance of forces resulting in deviation from an initial path. Sharks have elongate bodies that bend substantially and, in combination with pectoral fin rotation, play a role in yaw (horizontal) turning, but previous studies focus primarily on maximal turning performance rather than routine maneuvers. Routine maneuvering is largely understudied in fish swimming, despite observations that moderate maneuvering is much more common than the extreme behaviors commonly described in the literature. In this study, we target routine maneuvering in the bonnethead shark, Sphyrna tiburo. We use video reconstruction of moving morphology to describe three-dimensional pectoral fin rotation about three axes to compare to those previously described on yaw turning by the Pacific spiny dogfish. We quantify kinematic variables to understand the impacts of body and fin movements on routine turning performance. We also describe the anatomy of bonnethead pectoral fins and use muscle stimulation to confirm functional hypotheses about their role in actuating the fin. The turning performance metrics we describe for bonnethead sharks are comparable to other routine maneuvers described for the Pacific spiny dogfish and manta rays. These turns were substantially less agile and maneuverable than previously documented for other sharks, which we hypothesize results from the comparison of routine turning to maneuvering under stimulated conditions. We suggest that these results highlight the importance of considering routine maneuvering in future studies. Cinemática del Cuerpo y de las Aletas Pectorales Durante el giro en el eje Vertical en la Cabeza del Tiburón Pala (Sphyrna tiburo) (Body and Pectoral Fin Kinematics During Routine Yaw Turning in Bonnethead Sharks [Sphyrna tiburo]).

Maniobrar es una estrategia locomotora crucial entre los vertebrados acuáticos, la usan communmente al nadar, alimentarse y escapar. Las combinación de movimientos de todo el cuerpo y las aletas generan un desequilibrio de fuerzas que resulta en una desviación de una trayectoria inicial. Los tiburones tienen cuerpos alargados que se doblan sustancialmente y, en combinación con la rotación de la aleta pectoral, desempeñan un papel en el giro de horizontal de la cabez. Estudios anteriores se centraron principalmente en el rendimiento máximo de giro en lugar de las maniobras de rutina. Las maniobras de rutina son poco estudiadas en la natación de peces, a pesar de las observaciones de que las maniobras moderadas son mucho más comunes que las conductas extremas comúnmente descritas en la literatura. Utilizamos la reconstrucción con video de la morfología en movimiento para describir la rotación de la aleta pectoral tridimensional en tres ejes para compararla con los descritos anteriormente en un estudio sobre el giro de rutina realizado por el tiburón espinoso del Pacífico. Cuantificamos las variables cinemáticas para comprender los impactos de los movimientos del cuerpo y las aletas en el rendimiento de giro de rutina. También describimos la anatomía de las aletas pectorales tiburón cabeza de pala y utilizamos la estimulación muscular para confirmar las hipótesis funcionales sobre su papel en la actuación de la aleta. Las métricas de rendimiento de giro que describimos para los tiburones cabeza de pala son comparables a otras maniobras de rutina descritas para el perrito espinoso del Pacífico y las mantas rayas. Estos giros fueron sustancialmente menos ágiles y maniobrables de lo que se documentó anteriormente para otros tiburones, lo cual, según nuestra hipótesis, resulta de la comparación del giro rutinario a la maniobra en condiciones estimuladas. Sugerimos que estos resultados resaltan la importancia de considerar maniobras rutinarias en estudios futuros. Translated to Spanish by J. Heras (herasj01@gmail.com).

Cinemática do Corpo e da Nadadeira Peitoral Durante a Rotação de Rotina em Tubarões Cabeça-de-Boné (Sphyrna tiburo) (Body and Pectoral Fin Kinematics During Routine Yaw Turning in Bonnethead Sharks [Sphyrna tiburo]) A manobra é uma estratégia locomotora crucial entre os vertebrados aquáticos, comum na natação rotineira, na alimentação e na resposta à ameaças. Combinações de movimentos do corpo e das nadadeiras geram um desequilíbrio de forças resultando em desvio do caminho inicial. Os tubarões têm corpos alongados que se dobram substancialmente e, em combinação com a rotação da nadadeira peitoral, desempenham um papel importante no giro horizontal (guinada), porém, estudos anteriores focaram principalmente no desempenho de giro máximo em vez de manobras rotineiras. A manobra rotineira é pouco estudada na natação de peixes, apesar das observações de que manobras moderadas são muito mais comuns do que os comportamentos extremos comumente reportados em literatura. Usamos a reconstrução de vídeo de morfologia móvel para descrever a rotação tridimensional da nadadeira peitoral para comparar com aqueles previamente descritos em um estudo sobre rotação rotineira pelo tubarão galhudo do Pacífico. Quantificamos as variáveis cinemáticas para entender os impactos dos movimentos do corpo e das nadadeiras no desempenho rotineiro de giro. Descrevemos também a anatomia das nadadeiras peitorais do tubarão martelo e utilizamos a estimulação muscular para confirmar hipóteses funcionais sobre o seu papel na movimentação da nadadeira. As métricas de desempenho de giro que descrevemos para os tubarões martelo são comparáveis a outras manobras de rotina descritas para o tubarão galhudo do Pacífico e raias-manta. Esses turnos foram substancialmente menos ágeis e manobráveis do que o anteriormente documentado para outros tubarões, dados dos quais nós criamos a hipótese com os resultados da comparação da rotação de rotina para manobrar sob condições estimuladas. Sugerimos que esses resultados ressaltem a importância de considerar manobras rotineiras em estudos futuros. Translated to Portuguese by Diego Vaz (dbistonvaz@vims.edu).

Built for speed: strain in the cartilaginous vertebral columns of sharks.

In most bony fishes vertebral column strain during locomotion is almost exclusively in the intervertebral joints, and when these joints move there is the potential to store and release strain energy. Since cartilaginous fishes have poorly mineralized vertebral centra, we tested whether the vertebral bodies undergo substantial strain and thus may be sites of energy storage during locomotion. We measured axial strains of the intervertebral joints and vertebrae in vivo and ex vivo to characterize the dynamic behavior of the vertebral column. We used sonomicrometry to directly measure in vivo and in situ strains of intervertebral joints and vertebrae of Squalus acanthias swimming in a flume. For ex vivo measurements, we used a materials testing system to dynamically bend segments of vertebral column at frequencies ranging from 0.25 to 1.00 Hz and a range of physiologically relevant curvatures, which were determined using a kinematic analysis. The vertebral centra of S. acanthias undergo strain during in vivo volitional movements as well as in situ passive movements. Moreover, when isolated segments of vertebral column were tested during mechanical bending, we measured the same magnitudes of strain. These data support our hypothesis that vertebral column strain in lateral bending is not limited to the intervertebral joints. In histological sections, we found that the vertebral column of S. acanthias has an intracentral canal that is open and covered with a velum layer. An open intracentral canal may indicate that the centra are acting as tunics around some sections of a hydrostat, effectively stiffening the vertebral column. These data suggest that the entire vertebral column of sharks, both joints and centra, is mechanically engaged as a dynamic spring during locomotion.

The N-DRC forms a conserved biochemical complex that maintains outer doublet alignment and limits microtubule sliding in motile axonemes.

The nexin-dynein regulatory complex (N-DRC) is proposed to coordinate dynein arm activity and interconnect doublet microtubules. Here we identify a conserved region in DRC4 critical for assembly of the N-DRC into the axoneme. At least 10 subunits associate with DRC4 to form a discrete complex distinct from other axonemal substructures. Transformation of drc4 mutants with epitope-tagged DRC4 rescues the motility defects and restores assembly of missing DRC subunits and associated inner-arm dyneins. Four new DRC subunits contain calcium-signaling motifs and/or AAA domains and are nearly ubiquitous in species with motile cilia. However, drc mutants are motile and maintain the 9 + 2 organization of the axoneme. To evaluate the function of the N-DRC, we analyzed ATP-induced reactivation of isolated axonemes. Rather than the reactivated bending observed with wild-type axonemes, ATP addition to drc-mutant axonemes resulted in splaying of doublets in the distal region, followed by oscillatory bending between pairs of doublets. Thus the N-DRC provides some but not all of the resistance to microtubule sliding and helps to maintain optimal alignment of doublets for productive flagellar motility. These findings provide new insights into the mechanisms that regulate motility and further highlight the importance of the proximal region of the axoneme in generating flagellar bending.

From a declaration of values to the creation of value in global health: a report from Harvard University's Global Health Delivery Project.

To make best use of the new dollars available for the treatment of disease in resource-poor settings, global health practice requires a strategic approach that emphasises value for patients. Practitioners and global health academics should seek to identify and elaborate the set of factors that drives value for patients through the detailed study of actual care delivery organisations in multiple settings. Several frameworks can facilitate this study, including the care delivery value chain. We report on our efforts to catalyse the study of health care delivery in resource-limited settings in the hope that this inquiry will lead to insights that can improve the health of the neediest worldwide.

Requirement for the molecular adapter function of StpA at the Escherichia coli bgl promoter depends upon the level of truncated H-NS protein.

Truncated derivatives of the Escherichia coli nucleoid-associated protein H-NS that lack the DNA-binding domain remain competent for silencing of the cryptic bgl operon in vivo. Previous studies have provided evidence for the involvement of either the homologous nucleoid protein StpA or the alternative sigma factor RpoS in this unusual silencing mechanism. Here, we rationalize this apparent discrepancy. We show that two hns alleles (hns-205::Tn10 and hns60), which produce virtually identical amino-terminal fragments of H-NS, have very different requirements for StpA to mediate bgl silencing. The hns60 allele produces a high level of truncated H-NS, which can overcome the absence of StpA, whereas the lower level expressed by hns-205::Tn10 requires StpA for silencing. Reversing the relative levels of the two H-NS fragments reverses their requirement for StpA to silence bgl transcription. This suggests that the amino-terminal fragment of H-NS can be targeted to DNA to mediate silencing by multiple protein-protein interactions. The high-specificity interaction with StpA can function at low levels of truncated H-NS, whereas an alternative mechanism, perhaps involving lower specificity interactions with another protein(s), is only functional when truncated H-NS is abundant. These findings have important implications for the involvement of other proteins in H-NS-dependent transcriptional repression.

Adverse hemodynamic effects of interrupting chest compressions for rescue breathing during cardiopulmonary resuscitation for ventricular fibrillation cardiac arrest.

BACKGROUND: Despite improving arterial oxygen saturation and pH, bystander cardiopulmonary resuscitation (CPR) with chest compressions plus rescue breathing (CC+RB) has not improved survival from ventricular fibrillation (VF) compared with chest compressions alone (CC) in numerous animal models and 2 clinical investigations. METHODS AND RESULTS: After 3 minutes of untreated VF, 14 swine (32+/-1 kg) were randomly assigned to receive CC+RB or CC for 12 minutes, followed by advanced cardiac life support. All 14 animals survived 24 hours, 13 with good neurological outcome. For the CC+RB group, the aortic relaxation pressures routinely decreased during the 2 rescue breaths. Therefore, the mean coronary perfusion pressure of the first 2 compressions in each compression cycle was lower than those of the final 2 compressions (14+/-1 versus 21+/-2 mm Hg, P<0.001). During each minute of CPR, the number of chest compressions was also lower in the CC+RB group (62+/-1 versus 92+/-1 compressions, P<0.001). Consequently, the integrated coronary perfusion pressure was lower with CC+RB during each minute of CPR (P<0.05 for the first 8 minutes). Moreover, at 2 to 5 minutes of CPR, the median left ventricular blood flow by fluorescent microsphere technique was 60 mL. 100 g(-1). min(-1) with CC+RB versus 96 mL. 100 g(-1). min(-1) with CC, P<0.05. Because the arterial oxygen saturation was higher with CC+RB, the left ventricular myocardial oxygen delivery did not differ. CONCLUSIONS: Interrupting chest compressions for rescue breathing can adversely affect hemodynamics during CPR for VF.

The Chlamydomonas PF6 locus encodes a large alanine/proline-rich polypeptide that is required for assembly of a central pair projection and regulates flagellar motility.

Efficient motility of the eukaryotic flagellum requires precise temporal and spatial control of its constituent dynein motors. The central pair and its associated structures have been implicated as important members of a signal transduction cascade that ultimately regulates dynein arm activity. To identify central pair components involved in this process, we characterized a Chlamydomonas motility mutant (pf6-2) obtained by insertional mutagenesis. pf6-2 flagella twitch ineffectively and lack the 1a projection on the C1 microtubule of the central pair. Transformation with constructs containing a full-length, wild-type copy of the PF6 gene rescues the functional, structural, and biochemical defects associated with the pf6 mutation. Sequence analysis indicates that the PF6 gene encodes a large polypeptide that contains numerous alanine-rich, proline-rich, and basic domains and has limited homology to an expressed sequence tag derived from a human testis cDNA library. Biochemical analysis of an epitope-tagged PF6 construct demonstrates that the PF6 polypeptide is an axonemal component that cosediments at 12.6S with several other polypeptides. The PF6 protein appears to be an essential component required for assembly of some of these polypeptides into the C1-1a projection.

Strategy and the Internet.

Many of the pioneers of Internet business, both dot-coms and established companies, have competed in ways that violate nearly every precept of good strategy. Rather than focus on profits, they have chased customers indiscriminately through discounting, channel incentives, and advertising. Rather than concentrate on delivering value that earns an attractive price from customers, they have pursued indirect revenues such as advertising and click-through fees. Rather than make trade-offs, they have rushed to offer every conceivable product or service. It did not have to be this way--and it does not have to be in the future. When it comes to reinforcing a distinctive strategy, Michael Porter argues, the Internet provides a better technological platform than previous generations of IT. Gaining competitive advantage does not require a radically new approach to business; it requires building on the proven principles of effective strategy. Porter argues that, contrary to recent thought, the Internet is not disruptive to most existing industries and established companies. It rarely nullifies important sources of competitive advantage in an industry; it often makes them even more valuable. And as all companies embrace Internet technology, the Internet itself will be neutralized as a source of advantage. Robust competitive advantages will arise instead from traditional strengths such as unique products, proprietary content, and distinctive physical activities. Internet technology may be able to fortify those advantages, but it is unlikely to supplant them. Porter debunks such Internet myths as first-mover advantage, the power of virtual companies, and the multiplying rewards of network effects. He disentangles the distorted signals from the marketplace, explains why the Internet complements rather than cannibalizes existing ways of doing business, and outlines strategic imperatives for dot-coms and traditional companies.

Insights into the structural organization of the I1 inner arm dynein from a domain analysis of the 1beta dynein heavy chain.

To identify domains in the dynein heavy chain (Dhc) required for the assembly of an inner arm dynein, we characterized a new motility mutant (ida2-6) obtained by insertional mutagenesis. ida2-6 axonemes lack the polypeptides associated with the I1 inner arm complex. Recovery of genomic DNA flanking the mutation indicates that the defects are caused by plasmid insertion into the Dhc10 transcription unit, which encodes the 1beta Dhc of the I1 complex. Transformation with Dhc10 constructs encoding <20% of the Dhc can partially rescue the motility defects by reassembly of an I1 complex containing an N-terminal 1beta Dhc fragment and a full-length 1alpha Dhc. Electron microscopic analysis reveals the location of the missing 1beta Dhc motor domain within the axoneme structure. These observations, together with recent studies on the 1alpha Dhc, identify a Dhc domain required for complex assembly and further demonstrate that the intermediate and light chains are associated with the stem regions of the Dhcs in a distinct structural location. The positioning of these subunits within the I1 structure has significant implications for the pathways that target the assembly of the I1 complex into the axoneme and modify the activity of the I1 dynein during flagellar motility.

The Rib43a protein is associated with forming the specialized protofilament ribbons of flagellar microtubules in Chlamydomonas.

Ciliary and flagellar microtubules contain a specialized set of three protofilaments, termed ribbons, that are composed of tubulin and several associated proteins. Previous studies of sea urchin sperm flagella identified three of the ribbon proteins as tektins, which form coiled-coil filaments in doublet microtubules and which are associated with basal bodies and centrioles. To study the function of tektins and other ribbon proteins in the assembly of flagella and basal bodies, we have begun an analysis of ribbons from the unicellular biflagellate, Chlamydomonas reinhardtii, and report here the molecular characterization of the ribbon protein rib43a. Using antibodies against rib43a to screen an expression library, we recovered a full-length cDNA clone that encodes a 42,657-Da polypeptide. On Northern blots, the rib43a cDNA hybridized to a 1. 7-kb transcript, which was up-regulated upon deflagellation, consistent with a role for rib43a in flagellar assembly. The cDNA was used to isolate RIB43a, an approximately 4.6-kb genomic clone containing the complete rib43a coding region, and restriction fragment length polymorphism analysis placed the RIB43a gene on linkage group III. Sequence analysis of the RIB43a gene indicates that the substantially coiled-coil rib43a protein shares a high degree of sequence identity with clones from Trypanosoma cruzi and Homo sapiens (genomic, normal fetal kidney, and endometrial and germ cell tumors) but little sequence similarity to other proteins including tektins. Affinity-purified antibodies against native and bacterially expressed rib43a stained both flagella and basal bodies by immunofluorescence microscopy and stained isolated flagellar ribbons by immuno-electron microscopy. The structure of rib43a and its association with the specialized protofilament ribbons and with basal bodies is relevant to the proposed role of ribbons in forming and stabilizing doublet and triplet microtubules and in organizing their three-dimensional structure.

Domains in the 1alpha dynein heavy chain required for inner arm assembly and flagellar motility in Chlamydomonas.

Flagellar motility is generated by the activity of multiple dynein motors, but the specific role of each dynein heavy chain (Dhc) is largely unknown, and the mechanism by which the different Dhcs are targeted to their unique locations is also poorly understood. We report here the complete nucleotide sequence of the Chlamydomonas Dhc1 gene and the corresponding deduced amino acid sequence of the 1alpha Dhc of the I1 inner dynein arm. The 1alpha Dhc is similar to other axonemal Dhcs, but two additional phosphate binding motifs (P-loops) have been identified in the NH(2)- and COOH-terminal regions. Because mutations in Dhc1 result in motility defects and loss of the I1 inner arm, a series of Dhc1 transgenes were used to rescue the mutant phenotypes. Motile cotransformants that express either full-length or truncated 1alpha Dhcs were recovered. The truncated 1alpha Dhc fragments lacked the dynein motor domain, but still assembled with the 1beta Dhc and other I1 subunits into partially functional complexes at the correct axoneme location. Analysis of the transformants has identified the site of the 1alpha motor domain in the I1 structure and further revealed the role of the 1alpha Dhc in flagellar motility and phototactic behavior.

Cytoplasmic dynein heavy chain 1b is required for flagellar assembly in Chlamydomonas.

A second cytoplasmic dynein heavy chain (cDhc) has recently been identified in several organisms, and its expression pattern is consistent with a possible role in axoneme assembly. We have used a genetic approach to ask whether cDhc1b is involved in flagellar assembly in Chlamydomonas. Using a modified PCR protocol, we recovered two cDhc sequences distinct from the axonemal Dhc sequences identified previously. cDhc1a is closely related to the major cytoplasmic Dhc, whereas cDhc1b is closely related to the minor cDhc isoform identified in sea urchins, Caenorhabditis elegans, and Tetrahymena. The Chlamydomonas cDhc1b transcript is a low-abundance mRNA whose expression is enhanced by deflagellation. To determine its role in flagellar assembly, we screened a collection of stumpy flagellar (stf) mutants generated by insertional mutagenesis and identified two strains in which portions of the cDhc1b gene have been deleted. The two mutants assemble short flagellar stumps (<1-2 micrometer) filled with aberrant microtubules, raft-like particles, and other amorphous material. The results indicate that cDhc1b is involved in the transport of components required for flagellar assembly in Chlamydomonas.

Philanthropy's new agenda: creating value.

During the past two decades, the number of charitable foundations in the United States has doubled while the value of their assets has increased more than 1,100%. As new wealth continues to pour into foundations, the authors take a timely look at the field and conclude that radical change is needed. First, they explain why. Compared with direct giving, foundations are strongly favored through tax preferences whose value increases in rising stock markets. As a nation, then, we make a substantial investment in foundation philanthropy that goes well beyond the original gifts of private donors. We should therefore expect foundations to achieve a social impact disproportionate to their spending. If foundations serve merely as passive conduits for giving, then they not only fall far short of their potential but also fail to meet an important societal obligation. Drawing on Porter's work on competition and strategy, the authors then present a framework for thinking systematically about how foundations create value and how the various approaches to value creation can be deployed within the context of an overarching strategy. Although many foundations talk about "strategic" giving, much current practice is at odds with strategy. Among the common problems, foundations scatter their funding too broadly, they overlook the value-creating potential of longer and closer working relationships with grantees, and they pay insufficient attention to the ultimate results of the work they fund. This article lays out a blueprint for change, challenging foundation leaders to spearhead the evolution of philanthropy from private acts of conscience into a professional field.

The Chlamydomonas IDA7 locus encodes a 140-kDa dynein intermediate chain required to assemble the I1 inner arm complex.

To identify new loci that are involved in the assembly and targeting of dynein complexes, we have screened a collection of motility mutants that were generated by insertional mutagenesis. One such mutant, 5B10, lacks the inner arm isoform known as the I1 complex. This isoform is located proximal to the first radial spoke in each 96-nm axoneme repeat and is an important target for the regulation of flagellar motility. Complementation tests reveal that 5B10 represents a new I1 locus, IDA7. Biochemical analyses confirm that ida7 axonemes lack at least five I1 complex subunits. Southern blots probed with a clone containing the gene encoding the 140-kDa intermediate chain (IC) indicate that the ida7 mutation is the result of plasmid insertion into the IC140 gene. Transformation with a wild-type copy of the IC140 gene completely rescues the mutant defects. Surprisingly, transformation with a construct of the IC140 gene lacking the first four exons of the coding sequence also rescues the mutant phenotype. These studies indicate that IC140 is essential for assembly of the I1 complex, but unlike other dynein ICs, the N-terminal region is not critical for its activity.

Clusters and the new economics of competition.

Economic geography in an era of global competition poses a paradox. In theory, location should no longer be a source of competitive advantage. Open global markets, rapid transportation, and high-speed communications should allow any company to source any thing from any place at any time. But in practice, Michael Porter demonstrates, location remains central to competition. Today's economic map of the world is characterized by what Porter calls clusters: critical masses in one place of linked industries and institutions--from suppliers to universities to government agencies--that enjoy unusual competitive success in a particular field. The most famous example are found in Silicon Valley and Hollywood, but clusters dot the world's landscape. Porter explains how clusters affect competition in three broad ways: first, by increasing the productivity of companies based in the area; second, by driving the direction and pace of innovation; and third, by stimulating the formation of new businesses within the cluster. Geographic, cultural, and institutional proximity provides companies with special access, closer relationships, better information, powerful incentives, and other advantages that are difficult to tap from a distance. The more complex, knowledge-based, and dynamic the world economy becomes, the more this is true. Competitive advantage lies increasingly in local things--knowledge, relationships, and motivation--that distant rivals cannot replicate. Porter challenges the conventional wisdom about how companies should be configured, how institutions such as universities can contribute to competitive success, and how governments can promote economic development and prosperity.

The Shigella virulence gene regulatory cascade: a paradigm of bacterial gene control mechanisms.

Shigella flexneri is the causative agent of bacillary dysentery and is a facultative intracellular pathogen. Its virulence regulon is subject to tight control by several mechanisms involving the products of over 20 genes and an array of environmental signals. The reguIon is carried on a plasmid that is prone to instability and to integration into the chromosome, with associated silencing of the virulence genes. Closely related regulons are found in other species of Shigella and in enteroinvasive Escherichia coli. A wealth of detailed information is now available on the Shigella virulence gene control circuits, and it is becoming clear that these share many features with regulatory systems found in other bacterial pathogens. All of this makes the S. flexneri virulence gene control system a very attractive topic for those interested in the nature of gene regulatory networks in bacteria.