The Pluto system: Initial results from its exploration by New Horizons.

The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.

Myofiber injury and regeneration in a canine homologue of Duchenne muscular dystrophy.

OBJECTIVE: To test the hypothesis that differential skeletal muscle involvement, previously observed in dogs with a homologue of Duchenne muscular dystrophy, correlates with the histochemical markers of myofiber injury and regeneration. DESIGN: Evidence of injury (cellular penetration by Evans blue dye, immunoglobulin G expression, hematoxylin and eosin staining of necrotic figures), myofiber regeneration (fetal myosin heavy chain isoform expression), and morphologic indices in the cranial sartorius (CS), long digital extensor, and vastus lateralis muscles were examined in five dogs with dystrophy and five normal dogs. RESULTS: Only the CS muscle, at 1 mo, demonstrated significant differences in injury when compared with age-matched controls. By 6 mo, the long digital extensor and vastus lateralis also suffered greater than normal injury. Only the dystrophic CS tissue expressed a notable increase in mean myofiber diameter when compared with other muscles at 6 mo. Normal CS muscles revealed a distinct population of small myofibers at this age. CONCLUSION: The CS seems unique in its selective pathologic involvement. These differences may contribute to the marked regenerative response of this muscle in the dystrophic state. An improved understanding of mechanisms by which some dystrophin-deficient canine muscles remain spared from injury may provide clues to investigate and prevent the degenerative processes in humans.

In vivo targeted repair of a point mutation in the canine dystrophin gene by a chimeric RNA/DNA oligonucleotide.

In the canine model of Duchenne muscular dystrophy in golden retrievers (GRMD), a point mutation within the splice acceptor site of intron 6 leads to deletion of exon 7 from the dystrophin mRNA, and the consequent frameshift causes early termination of translation. We have designed a DNA and RNA chimeric oligonucleotide to induce host cell mismatch repair mechanisms and correct the chromosomal mutation to wild type. Direct skeletal muscle injection of the chimeric oligonucleotide into the cranial tibialis compartment of a six-week-old affected male dog, and subsequent analysis of biopsy and necropsy samples, demonstrated in vivo repair of the GRMD mutation that was sustained for 48 weeks. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of exons 5-10 demonstrated increasing levels of exon 7 inclusion with time. An isolated exon 7-specific dystrophin antibody confirmed synthesis of normal-sized dystrophin product and positive localization to the sarcolemma. Chromosomal repair in muscle tissue was confirmed by restriction fragment length polymorphism (RFLP)-PCR and sequencing the PCR product. This work provides evidence for the long-term repair of a specific dystrophin point mutation in muscle of a live animal using a chimeric oligonucleotide.

Contraction force generated by tarsal joint flexion and extension in dogs with golden retriever muscular dystrophy.

Force generated due to torque caused by tarsal joint flexion and extension was measured noninvasively at 3, 4.5, 6, and 12 months of age in dogs with the Duchenne homologue, golden retriever muscular dystrophy (GRMD). Absolute and body-weight-corrected GRMD twitch and tetanic force values were lower than normal at all ages (P<0.01 for most). Tarsal flexion and extension were differentially affected. Flexion values were especially low at 3 months, whereas extension was affected more at later ages. Several other GRMD findings differed from normal. The twitch/tetany ratio was generally lower; post-tetanic potentiation for flexion values was less marked; and extension relaxation and contraction times were longer. The consistency of GRMD values was studied to determine which measurements will be most useful in evaluating treatment outcome. Standard deviation was proportionally greater for GRMD versus normal recordings. More consistent values were seen for tetany versus twitch and for flexion versus extension. Left and right limb tetanic flexion values did not differ in GRMD; extension values were more variable. These results suggest that measurement of tarsal tetanic force should be most useful to document therapeutic benefit in GRMD dogs.

Evaluating motor end-plate-targeted injections of botulinum toxin type A in a canine model.

Tarsal joint forces were measured in dogs over 70 days following botulinum toxin type A (BTX-A) injections. Three dogs were injected at motor end-plates located by electromyography (EMG), while 3 dogs were similarly injected, but without EMG guidance. Extension forces were significantly (P < 0.05) smaller in limbs injected at motor end-plates than in corresponding limbs on days 14 and 35. There were no significant differences at other times. Using these techniques, EMG end-plate targeting potentiates effects of BTX-A.

Mutation segregation and rapid carrier detection of X-linked muscular dystrophy in dogs.

OBJECTIVES: To use exon 7-specific genomic polymerase chain reaction (PCR) products to identify the genotypes of normal, affected, and carrier female dogs in pedigrees segregating Golden Retriever muscular dystrophy (GRMD), and to confirm the concordant segregation of the mutation in all carrier and affected dogs presently available. DESIGN: The GRMD mutation is found in the consensus splice acceptor site in intron 6 of the canine dystrophin gene. PCR cycle-sequencing and restriction fragment length polymorphism/PCR were used for determination of the pattern of segregation of the point mutation which causes GRMD. ANIMALS: Normal, clinically affected, and obligate carrier dogs in pedigrees of GRMD. PROCEDURE: DNA from blood was amplified, using PCR and primers that bracket all of exon 7 of the canine dystrophin gene as well as 100 base pairs of intron on either side. PCR products were either cycle-sequenced directly or submitted to a second round of PCR, using 1 of the original primers coupled with a mutagenic restriction fragment length polymorphism-primer, which thus creates an artificial restriction site. Digestion with Stu I detected the normal allele. To detect the affected allele, Sau96 I was used to digest the 310-base pair exon 7 genomic fragment directly. CONCLUSIONS: Simple, clear diagnosis of carrier status was possible using these methods. This mutation is passed through all carrier and affected dogs in both United States GRMD colonies and the colony in Australia. CLINICAL RELEVANCE: Rapid, accurate diagnosis of carrier and affected dogs will enhance study of this homologue of Duchenne muscular dystrophy.

Contraction tension and kinetics of the peroneus longus muscle in golden retriever muscular dystrophy.

Contraction tension and kinetics of the peroneus longus muscle were studied in dogs with the Duchenne homologue, golden retriever muscular dystrophy (GRMD), in advance of evaluating localized therapies such as myoblast transplantation. Absolute and both muscle- and body-weight-corrected twitch tension in GRMD dogs were low compared to normal litter mates at 3 months of age (p < 0.0005 for all). Tetanic tension was affected similarly. However, whereas absolute values were still reduced at 6 months (p < 0.0005 for twitch and 0.005 for tetany), twitch and tetanic tension corrected for either muscle or body weight was not statistically different, suggesting that the peroneus longus may be relatively spared in GRMD. Post-tetanic potentiation was more pronounced in GRMD versus normal dogs at both 3 (p < 0.0001) and 6 (p < 0.01) months. The degree of positive staircase at 3 months of age did not differ. Twitch contraction and relaxation times were dramatically prolonged, and there was concomitant sustained electrical activity, at, or before, 6 months of age in some severely affected dogs. Relatively few carriers were evaluated at these ages, but their values were similar to those of normal dogs. Apparent sparing of the peroneus longus muscle may limit application of this technique to evaluation of therapies administered early in life or in combination with toxins. Treatment to alter changes in contraction kinetics could also be assessed.