Dental morphology and microstructure of the Prickly Dogfish Oxynotus bruniensis (Squaliformes: Oxynotidae).

This study describes and illustrates the jaws, teeth, and tooth microstructure of the Prickly Dogfish Oxynotus bruniensis. Detailed accounts of the dental morphology of O. bruniensis are rare and have not addressed the tissue arrangement or microstructure of the teeth. These features are documented and discussed in the contexts of interspecific comparisons with other elasmobranchs and the dietary specialization of O. bruniensis. The overall tooth morphology of O. bruniensis is similar to those of other closely related members in the order Squaliformes, as is the tissue arrangement, or histotype. Oxynotus bruniensis exhibits a simplified enameloid microstructure, which we compare with previously documented enameloid microstructures of other elasmobranchs. Though subtle interspecific differences in dental characters are documented, neither overall tooth morphology nor histotype and microstructure are unique to O. bruniensis. We conclude that in the case of O. bruniensis, dietary specialization is facilitated by behavioral rather than morphological specialization.

Surgeon Ability to Appropriately Address the Calcified Cartilage Layer: An In Vitro Study of Arthroscopic and Open Techniques.

BACKGROUND: Microfracture is a commonly utilized cartilage restoration technique for articular cartilage defects. While the removal of the calcified cartilage layer (CCL) has been shown to be critical with in vivo models, little is known with regard to surgeon reliability to adequately perform the technique. PURPOSE: To evaluate surgeon reliability in removing the CCL utilizing open and arthroscopic techniques. STUDY DESIGN: Controlled laboratory study. METHODS: Eleven cadaveric knees were utilized to create four 12-mm diameter defects in the anterior and posterior medial femoral condyles. Eleven fellowship-trained surgeons were asked to perform the following procedures: remove the CCL open, retain the CCL open, remove the CCL arthroscopically, and retain the CCL arthroscopically. Samples underwent histologic staining and analysis with 3-dimensional micro-computed tomography. The latter was used to calculate the percentage of the CCL that was removed or retained across the entire defect. RESULTS: When surgeons were asked to retain the CCL arthroscopically, 48% ± 41% (mean ± SD) remained. When surgeons were asked to remove the CCL arthroscopically, 24% ± 35% remained. There was no statistical difference between these groups (P > .05). When the CCL was retained during open preparation, 60% ± 39% remained. During attempts to remove the CCL in an open manner, 19% ± 28% remained. There was a significant difference in the amount of CCL remaining between the open removal and open retaining groups (P = .03). There were no significant differences in the percentage of CCL remaining between the open and arthroscopic preservation groups and between the open and arthroscopic removal groups. CONCLUSION/CLINICAL RELEVANCE: This study highlights the significant variability in surgeon ability to reliably retain or remove the CCL. However, there appears to be improved ability of surgeons to more reliably remove or retain the CCL in an open fashion as compared with the arthroscopic approach.

Changes in growth rates of oral jaw elements produce evolutionary novelty in bahamian pupfish.

To understand the origins of novelty and the evolution of biological diversity, it is important to investigate the processes that generate phenotypic variation from genotypic variation. A number of path-breaking studies have revealed the genetic basis for phenotypic differences between distantly related taxa, but how qualitative change is produced during the early stages of divergence is largely unexplored. Here, we focus on striking differences in jaw morphology exhibited by three closely related sympatric pupfish species (genus Cyprinodon) from San Salvador Island, Bahamas as a basis for investigating the genetic sources of morphological variation in recently diverged species. San Salvador Island pupfish are trophically diverse and display derived jaw morphologies distinct from any other species in the genus. We illustrate these qualitative morphological differences between species with 3D-reconstructed CT-images and camera lucida drawings of the skulls of wild-caught fish. Quantitative data representing the size of individual bony skull elements in wild fish show how qualitatively novel morphologies arise as a consequence of changes to the size and shape of individual skull elements, particularly the dentary, premaxilla, and maxilla bones associated with the oral jaws. Consistent with these comparative data is that the growth rate of individual bony skull elements, measured on a developmental time series of lab-reared fish, differs between species. Our data provide a critical foundation for future studies developing San Salvador Cyprinodon pupfishes as a model system to understand the evolution and development of novel morphologies at the species level. J. Morphol. 277:935-947, 2016. © 2016 Wiley Periodicals, Inc.

Morphologically Specialized Termite Castes and Advanced Sociality in the Early Cretaceous.

A hallmark of animals that are eusocial, or those with advanced sociality, is reproductive specialization into worker and queen castes. In the most derived societies, these divisions are essentially fixed and in some arthropods, include further specialization--a tripartite system with a soldier caste that defends the colony. Eusociality has originated numerous times among insects but is believed to have appeared first in the termites (Isoptera), in the Early Cretaceous. However, all termites known from the Cretaceous have, until now, only been winged reproductives (alates and dealates); the earliest soldiers and definitive workers were known from just the Miocene (ca. 17-20 million years ago [mya]). Here, we report six termite species preserved in Early Cretaceous (ca. 100 mya) amber from Myanmar, one described as Krishnatermes yoddha gen. et sp. nov., comprising the worker/pseudergate, winged reproductive, and soldier, and a second species, Gigantotermes rex gen. et sp. nov., based on one of the largest soldier termites yet known. Phylogenetic analysis indicates that Krishnatermes are in the basal "Meiatermes-grade" of Cretaceous termites. Workers/pseudergates of another four species are briefly described, but not named. One of these workers/pseudergates reveals that ants--the most serious enemies of modern termites--lived in close proximity to termites in the Burmese paleofauna. These discoveries demonstrate the Mesozoic antiquity of specialized termite caste systems and corroborate that among all social species, termites probably had the original societies.

Long-Proboscid Flies as Pollinators of Cretaceous Gymnosperms.

The great evolutionary success of angiosperms has traditionally been explained, in part, by the partnership of these plants with insect pollinators. The main approach to understanding the origins of this pervasive relationship has been study of the pollinators of living cycads, gnetaleans, and basal angiosperms. Among the most morphologically specialized living pollinators are diverse, long-proboscid flies. Early such flies include the brachyceran family Zhangsolvidae, previously known only as compression fossils from the Early Cretaceous of China and Brazil. It belongs to the infraorder Stratiomyomorpha, a group that includes the flower-visiting families Xylomyidae and Stratiomyidae. New zhangsolvid specimens in amber from Spain (ca. 105 mega-annum [Ma]) and Myanmar (100 Ma) reveal a detailed proboscis structure adapted to nectivory. Pollen clumped on a specimen from Spain is Exesipollenites, attributed to a Mesozoic gymnosperm, most likely the Bennettitales. Late Mesozoic scorpionflies with a long proboscis have been proposed as specialized pollinators of various extinct gymnosperms, but pollen has never been observed on or in their bodies. The new discovery is a very rare co-occurrence of pollen with its insect vector and provides substantiating evidence that other long-proboscid Mesozoic insects were gymnosperm pollinators. Evidence is thus now gathering that visitors and probable pollinators of early anthophytes, or seed plants, involved some insects with highly specialized morphological adaptations, which has consequences for interpreting the reproductive modes of Mesozoic gymnosperms and the significance of insect pollination in angiosperm success.

Integrated 3D view of postmating responses by the Drosophila melanogaster female reproductive tract, obtained by micro-computed tomography scanning.

Physiological changes in females during and after mating are triggered by seminal fluid components in conjunction with female-derived molecules. In insects, these changes include increased egg production, storage of sperm, and changes in muscle contraction within the reproductive tract (RT). Such postmating changes have been studied in dissected RT tissues, but understanding their coordination in vivo requires a holistic view of the tissues and their interrelationships. Here, we used high-resolution, multiscale micro-computed tomography (CT) scans to visualize and measure postmating changes in situ in the Drosophila female RT before, during, and after mating. These studies reveal previously unidentified dynamic changes in the conformation of the female RT that occur after mating. Our results also reveal how the reproductive organs temporally shift in concert within the confines of the abdomen. For example, we observed chiral loops in the uterus and in the upper common oviduct that relax and constrict throughout sperm storage and egg movement. We found that specific seminal fluid proteins or female secretions mediate some of the postmating changes in morphology. The morphological movements, in turn, can cause further changes due to the connections among organs. In addition, we observed apparent copulatory damage to the female intima, suggesting a mechanism for entry of seminal proteins, or other exogenous components, into the female's circulatory system. The 3D reconstructions provided by high-resolution micro-CT scans reveal how male and female molecules and anatomy interface to carry out and coordinate mating-dependent changes in the female's reproductive physiology.

Development and microstructure of tooth histotypes in the blue shark, Prionace glauca (Carcharhiniformes: Carcharhinidae) and the great white shark, Carcharodon carcharias (Lamniformes: Lamnidae).

Elasmobranchs exhibit two distinct arrangements of mineralized tissues in the teeth that are known as orthodont and osteodont histotypes. Traditionally, it has been said that orthodont teeth maintain a pulp cavity throughout tooth development whereas osteodont teeth are filled with osteodentine and lack a pulp cavity when fully developed. We used light microscopy, scanning electron microscopy, and high-resolution micro-computed tomography to compare the structure and development of elasmobranch teeth representing the two histotypes. As an example of the orthodont histotype, we studied teeth of the blue shark, Prionace glauca (Carcharhiniformes: Carcharhinidae). For the osteodont histotype, we studied teeth of the great white shark, Carcharodon carcharias (Lamniformes: Lamnidae). We document similarities and differences in tooth development and the microstructure of tissues in these two species and review the history of definitions and interpretations of elasmobranch tooth histotypes. We discuss a possible correlation between tooth histotype and tooth replacement and review the history of histotype differentiation in sharks. We find that contrary to a long held misconception, there is no orthodentine in the osteodont teeth of C. carcharias.

Growth pattern analysis of murine lung neoplasms by advanced semi-automated quantification of micro-CT images.

Computed tomography (CT) is a non-invasive imaging modality used to monitor human lung cancers. Typically, tumor volumes are calculated using manual or semi-automated methods that require substantial user input, and an exponential growth model is used to predict tumor growth. However, these measurement methodologies are time-consuming and can lack consistency. In addition, the availability of datasets with sequential images of the same tumor that are needed to characterize in vivo growth patterns for human lung cancers is limited due to treatment interventions and radiation exposure associated with multiple scans. In this paper, we performed micro-CT imaging of mouse lung cancers induced by overexpression of ribonucleotide reductase, a key enzyme in nucleotide biosynthesis, and developed an advanced semi-automated algorithm for efficient and accurate tumor volume measurement. Tumor volumes determined by the algorithm were first validated by comparison with results from manual methods for volume determination as well as direct physical measurements. A longitudinal study was then performed to investigate in vivo murine lung tumor growth patterns. Individual mice were imaged at least three times, with at least three weeks between scans. The tumors analyzed exhibited an exponential growth pattern, with an average doubling time of 57.08 days. The accuracy of the algorithm in the longitudinal study was also confirmed by comparing its output with manual measurements. These results suggest an exponential growth model for lung neoplasms and establish a new advanced semi-automated algorithm to measure lung tumor volume in mice that can aid efforts to improve lung cancer diagnosis and the evaluation of therapeutic responses.

Massive, solidified bone in the wing of a volant courting bird.

One pervasive morphological feature of tetrapods is the pipe-like, often marrow-filled, structure of the limb or long bones. This 'hollow' form maximizes flexural strength and stiffness with the minimum amount of bony material, and is exemplified by truly hollow (air-filled), or pneumatic, humeri in many modern birds. High-resolution microCT scans of the wings of two male club-winged manakins (Machaeropterus deliciosus) uncovered a notable exception to the hollow-tube rule in terrestrial vertebrates; males exhibited solidified ulnae more than three times the volume of birds of comparable body size, with significantly higher tissue mineral densities. The humeri exhibited similar (but less extreme) modifications. Each of the observed osteological modifications increases the overall mass of the bone, running counter to pervasive weight-reducing optimizations for flight in birds. The club-winged manakin is named for a pair of unique wing feathers found in adult males; these enlarged feathers attach directly to the ulna and resonate to produce a distinctive sound used in courtship displays. Given that the observed modifications probably assist in sound production, the club-winged manakin represents a case in which sexual selection by female choice has generated an ecologically 'costly' forelimb morphology, unique in being specialized for sound production at a presumed cost in flight efficiency.

Disease severity in a mouse model of ataxia telangiectasia is modulated by the DNA damage checkpoint gene Hus1.

The human genomic instability syndrome ataxia telangiectasia (A-T), caused by mutations in the gene encoding the DNA damage checkpoint kinase ATM, is characterized by multisystem defects including neurodegeneration, immunodeficiency and increased cancer predisposition. ATM is central to a pathway that responds to double-strand DNA breaks, whereas the related kinase ATR leads a parallel signaling cascade that is activated by replication stress. To dissect the physiological relationship between the ATM and ATR pathways, we generated mice defective for both. Because complete ATR pathway inactivation causes embryonic lethality, we weakened the ATR mechanism to different degrees by impairing HUS1, a member of the 911 complex that is required for efficient ATR signaling. Notably, simultaneous ATM and HUS1 defects caused synthetic lethality. Atm/Hus1 double-mutant embryos showed widespread apoptosis and died mid-gestationally. Despite the underlying DNA damage checkpoint defects, increased DNA damage signaling was observed, as evidenced by H2AX phosphorylation and p53 accumulation. A less severe Hus1 defect together with Atm loss resulted in partial embryonic lethality, with the surviving double-mutant mice showing synergistic increases in genomic instability and specific developmental defects, including dwarfism, craniofacial abnormalities and brachymesophalangy, phenotypes that are observed in several human genomic instability disorders. In addition to identifying tissue-specific consequences of checkpoint dysfunction, these data highlight a robust, cooperative configuration for the mammalian DNA damage response network and further suggest HUS1 and related genes in the ATR pathway as candidate modifiers of disease severity in A-T patients.

Off-site control of repolarization alternans in cardiac fibers.

Repolarization alternans, a beat-to-beat alternation in action potential duration, has been putatively linked to the onset of cardiac reentry. Anti-alternans control strategies can eliminate alternans in individual cells by exploiting the rate dependence of action potential duration. The same approach, when applied to a common measuring/stimulating site at one end of a cardiac fiber, has been shown to have limited spatial efficacy. As a first step toward spatially distributed electrode control systems, we investigated "off-site" control in canine Purkinje fibers, in which the recording and control sites are different. We found experimentally that alternans can be eliminated at, or very near, the recording site, and that varying the location of the recording site along the fiber causes the node (the location with no alternans) to move along the fiber in close proximity to the recording site. Theoretical predictions based on an amplitude equation [B. Echebarria and A. Karma, Chaos 12, 923 (2002)] show that those findings follow directly from the wave nature of alternans: the most unstable mode of alternans along the fiber is a wave solution of a one-dimensional Helmholtz equation with a node position that only deviates slightly from the recording site by an amount dependent on electrotonic coupling. Computer simulations using a Purkinje fiber model confirm these theoretical and experimental results. Although off-site alternans control does not suppress alternans along the entire fiber, our results indicate that placing the node away from the stimulus site reduces alternans amplitude along the fiber, and may therefore have implications for antiarrhythmic strategies based on alternans termination.

Dynamic mechanism for initiation of ventricular fibrillation in vivo.

BACKGROUND: Dynamically induced heterogeneities of repolarization may lead to wave-front destabilizations and initiation of ventricular fibrillation (VF). In a computer modeling study, we demonstrated that specific sequences of premature stimuli maximized dynamically induced spatial dispersion of refractoriness and predisposed the heart to the development of conduction block. The purpose of this study was to determine whether the computer model results pertained to the initiation of VF in dogs in vivo. METHODS AND RESULTS: Monophasic action potentials were recorded from right and left ventricular endocardium in anesthetized beagle dogs (n=11) in vivo. Restitution of action potential duration and conduction time and the effective refractory period after delivery of the basic stimulus (S(1)) and each of 3 premature stimuli (S(2), S(3), S(4)) were determined at baseline and during verapamil infusion. The effective refractory period data were used to determine the interstimulus intervals for a sequence of 4 premature stimuli (S(2)S(3)S(4)S(5)=CL(VF)) for which the computer model predicted maximal spatial dispersion of refractoriness. Delivery of CL(VF) was associated with discordant action potential duration alternans and induction of VF in all dogs. Verapamil decreased spatial dispersion of refractoriness by reducing action potential duration and conduction time restitution in a dose-dependent fashion, effects that were associated with reduced inducibility of VF with CL(VF). CONCLUSIONS: Maximizing dynamically induced spatial dispersion of repolarization appears to be an effective method for inducing VF. Reducing spatial dispersion of refractoriness by modulating restitution parameters can have an antifibrillatory effect in vivo.

Ultrasonically actuated silicon microprobes for cardiac signal recording.

In this paper, we report on ultrasonically actuated silicon thin microprobes that successfully penetrated canine cardiac tissue in vitro, and recorded the electrophysiological signals from multiple sites simultaneously within the heart wall. The penetration force--maximum force encountered by the probe during penetration--is found to reduce with increasing ultrasonic driving voltage, on both excised canine right ventricular muscle and chicken breast muscle. The rate of force decrease varies with tissue type and microprobe dimension. With ultrasonic actuation, the silicon microprobes are inserted into isolated perfused canine heart without breakage or significant buckling, under 10Vpp actuating voltage. Recordings were obtained from isolated perfused canine heart during pacing, following the induction of ventricular tachycardia, and during the transition from ventricular tachycardia to ventricular fibrillation. Local conduction velocity of 0.60 +/- 0.03 m/s was observed from the multichannel recordings from the canine right ventricular wall under epicardial pacing. The application of the ultrasonic microprobes in cardiac electrophysiology study can provide information for reconstruction of electrical wave propagation within the heart, which is important to understanding the mechanisms of cardiac arrhythmias.

Control of electrical alternans in canine cardiac purkinje fibers.

Alternation in the duration of consecutive cardiac action potentials (electrical alternans) may precipitate conduction block and the onset of arrhythmias. Consequently, suppression of alternans using properly timed premature stimuli may be antiarrhythmic. To determine the extent to which alternans control can be achieved in cardiac tissue, isolated canine Purkinje fibers were paced from one end using a feedback control method. Spatially uniform control of alternans was possible when alternans amplitude was small. However, control became attenuated spatially as alternans amplitude increased. The amplitude variation along the cable was well described by a theoretically expected standing wave profile that corresponds to the first quantized mode of the one-dimensional Helmholtz equation. These results confirm the wavelike nature of alternans and may have important implications for their control using electrical stimuli.

Spatiotemporal transition to conduction block in canine ventricle.

Interruption of periodic wave propagation by the nucleation and subsequent disintegration of spiral waves is thought to mediate the transition from normal sinus rhythm to ventricular fibrillation. This sequence of events may be precipitated by a period doubling bifurcation, manifest as a beat-to-beat alternation, or alternans, of cardiac action potential duration and conduction velocity. How alternans causes the local conduction block required for initiation of spiral wave reentry remains unclear, however. In the present study, a mechanism for conduction block was derived from experimental studies in linear strands of cardiac tissue and from computer simulations in ionic and coupled maps models of homogeneous one-dimensional fibers. In both the experiments and the computer models, rapid periodic pacing induced marked spatiotemporal heterogeneity of cellular electrical properties, culminating in paroxysmal conduction block. These behaviors resulted from a nonuniform distribution of action potential duration alternans, secondary to alternans of conduction velocity. This link between period doubling bifurcations of cellular electrical properties and conduction block may provide a generic mechanism for the onset of tachycardia and fibrillation.