Topography and ice sheet collapse
Heinrich Events, in which large masses of icebergs rapidly break free from ice sheets, are thought to influence global climate by altering ocean circulation patterns with a large influx of freshwater. To investigate whether the changing height of the ice sheet may also influence global climate by altering atmospheric circulation, William Roberts et al. (pp. 16688–16693) simulated Heinrich Events in climate models, adjusting the models to consider freshwater influx only, changing ice sheet height only, or both factors together. The simulations, reconstructing Heinrich Events in Hudson Bay, resulted in widespread climate change. The authors found that the climate effects in the simulations that considered both freshwater influx and changing topography were not simply the sum of the climate effects of each component considered separately. In a simulation of changing ice sheet height only, warming was observed in the North Atlantic and in southeastern North America; both effects have been observed in the paleoclimate record and cannot be accounted for with freshwater influx models alone. The results suggest that altered atmospheric circulation due to changing ice sheet thickness is likely not the sole driver of climate change in Heinrich Events but may need to be considered in future climate models. — P.G.
Identifying areas of carbon storage potential
3D high-resolution LiDAR scan of road building activities in the Peruvian Amazon.
National strategies to mitigate carbon emissions through conserving carbon-sequestering ecosystems require accurate and high-resolution maps of both current terrestrial carbon storage and carbon emission threats. Gregory Asner et al. (pp. E5016–E5022) surveyed Peru using airborne light detection and ranging (LiDAR). Integrating 3D LiDAR data on vegetation structure with satellite imagery, the authors mapped current above-ground carbon storage, ranging from around zero metric tons per hectare at the coastal lowlands to more than 150 metric tons per hectare in humid Andean and Amazonian forests. The authors estimate that around 0.8 billion metric tons of above-ground stored carbon in Peru is at risk of loss to the atmosphere due to development activities. However, protected acreage, including nationally protected areas, privately held conserved land, and indigenous land, may be able to store nearly 3 billion metric tons of carbon. The authors identified areas in Amazonian lowland and submontane regions with high carbon storage densities that could store more than 2 billion metric tons of carbon if placed under protection from development. The results suggest that other developing tropical nations can use similar mapping techniques to rapidly assess terrestrial carbon emission mitigation resources, according to the authors. — P.G.
Blood collection and gene transcription
Several international consortia have recently launched large-scale genomics initiatives to characterize the molecular differences between normal and cancer cells. Such analyses, however, face the challenge of artifacts arising from biological and technical variability. Heidi Dvinge et al. (pp. 16802–16807) demonstrate that standard blood collection procedures can rapidly change the full range of messenger RNA molecules, or transcriptome, expressed by an organism’s hematopoietic cells. According to the authors, these changes can selectively activate specific biological pathways, trigger the expression of normally nonfunctional sequences such as pseudogenes and antisense RNAs, and alter RNA processing and quality control pathways. Furthermore, the authors report that thousands of genes can be affected, including those that participate in chromatin modification, RNA splicing, and T- and B-cell activation. In addition, the authors report biomarkers that indicate the overlong incubation of individual samples and reveal that keeping blood on ice can markedly reduce such alterations to the transcriptome. The findings highlight the potentially confounding effects of technical artifacts in cancer genomics data. — T.J.
Revival of 700-year-old viral genetic material
Ice core containing ancient caribou feces.
Ancient viral genetic material can illuminate viral evolution, but intact samples are rarely isolated from the environment. Terry Fei Fan Ng et al. (pp. 16842–16847) analyzed the viral genetic material contained in a core drilled through layers of accumulated caribou feces up to 4,000 years old in an ice patch in Canada’s Selwyn Mountains. Caribou congregate on ice patches to escape insects and summer heat, and deposit feces containing partially digested plant material. The authors isolated a complete viral DNA genome from a 700-year-old ice core layer that was distantly related to plant and fungi-infecting viruses, and a partial viral RNA genome that was related to an insect-infecting cripavirus. The appearance of the viral material in the fecal samples suggests that the viruses may have originated in plants eaten by the caribou or flying insects attracted to the material. Using a reverse genetics approach, the authors reconstituted the viral genome to determine whether the virus might infect plants. Nicotiana benthamiana plants inoculated with the ancient viral DNA displayed evidence of infection, including replication of viral DNA in inoculated and newly emerging leaves. According to the authors, cryogenically preserved environmental samples may preserve ancient viral genetic material for study. — J.P.J.
Proprioceptive feedback, walking, and swimming
Locomotion in mammals is believed to be controlled by a network of spinal neurons, referred to as a central pattern generator, but the role of proprioceptive sensory feedback from the muscle in modulating the normal locomotor pattern remains unclear. Turgay Akay et al. (pp. 16877–16882) employed an Egr3 mutant mouse, in which signaling from the muscle spindles, one of the two main classes of proprioceptors, is impaired. The authors used electromyography to measure muscular movements in hip, knee, and ankle joints of Egr3 mice. Egr3 mutants showed a marked defect in the timing of ankle flexor offset during walking, and mutants made more errors while walking on a horizontal ladder than wild-type mice. To investigate whether the impact of the Egr3 mutation reflects a compensatory function of the unaffected class of proprioceptors, known as the Golgi tendon organ (GTO) afferents, the authors examined Egr3 mutant mice during swimming, when GTO sensory activation is reduced or eliminated. Egr3 mice demonstrated impaired timing of all hindlimb muscles during swimming, similar to the effects observed when all proprioception was ablated. According to the authors, the study suggests that locomotion requires ongoing feedback from both muscle spindles and GTO afferents. — C.B.
Marijuana’s long-term effects on brain structures
Orbitofrontal cortex and connecting fiber tracts.
The effects of chronic marijuana use on brain structures are currently unclear. Francesca Filbey et al. (pp. 16913–16918) examined alterations in brain structures and connectivity while accounting for gender, age, ethnicity, age of first marijuana use, and duration of use. The authors studied 48 adult marijuana users and 62 gender- and age-matched nonusers, and report a number of differences in their brains’ gray matter volume, synchrony among abnormal grey matter regions during resting states, and white matter connectivity between abnormal grey matter regions. The findings suggest that chronic marijuana use may reduce the volume of grey matter and increase structural and functional connectivity in a structure known as the orbitofrontal cortex (OFC). Additional tests revealed that early onset of regular marijuana use may be associated with increased functional connectivity in white matter, whereas long duration of use might be tied to low structural connectivity. The preliminary findings suggest that gray matter in the OFC may be more vulnerable than white matter to the effects of δ-9-tetrahydrocannabinol, the main psychoactive ingredient in cannabis. According to the authors, the study suggests that chronic marijuana use might modulate complex neuroadaptive processes, but further studies are needed to determine whether these changes are reversible with discontinued marijuana use. — A.G.