Communication between the nose and brain of fruit flies
Fruit fly. Image courtesy of National Institute of General Medical Sciences.
The fruit fly Drosophila melanogaster has a three-level olfactory information processing system. The first level assembles information from other brain areas into a pattern of spikes and silences known as a combinatorial code. The second level breaks this code and passes the information onto the third level, where the odor label can be used to direct behavior. Charles Stevens (pp. 9460–9465) used the fruit fly olfactory system, which is a simple and well-studied model of olfaction, to unravel the mechanisms of odor coding and decoding. The author found that when the first information processing level sends information to the second level, only a small fraction of the roughly 2,000 second-layer neurons receive a large input. However, each odor activates a different population of large-input neurons, and only spikes from the small population of large-input neurons are relayed to the final level, while other neurons are inhibited. Information from the small population of neurons thus allows the third level to label an odor and direct appropriate behavior. Further research is needed to extend the conclusions reached about the fruit fly olfactory system to other three-layer systems, including the vertebrate cerebellum, hippocampus, and olfactory systems, according to the author. — L.G.
Mapping cytomegalovirus diversity in human hosts
Map summarizing HCMV genetic diversity.
Human cytomegalovirus (HCMV), part of the herpesvirus family, is a leading cause of transplantation failure and infection-related birth defects. The viral genome exhibits high genetic diversity within and between hosts, complicating vaccine development and promoting drug resistance. Nicholas Renzette et al. (pp. E4120–E4128) performed a large-scale genetic analysis of viral isolates from 17 congenitally infected infants to explore the patterns and limits of genomic diversity in this virus. The authors attempted to identify hot and cold spots of genetic variability in saliva, urine, and plasma samples. The findings reveal that viral diversity is unevenly distributed in the human body and across the viral genome. Viral populations isolated from plasma are genetically similar and enriched in glycoprotein and regulatory protein polymorphisms, even in hosts from different continents. Approximately one-quarter of the viral genome lacked polymorphisms, suggesting that the organism’s genomic diversity may have an upper limit. Further analyses revealed that viral diversity within an individual host is similar for mixed- and single-strain infections, and that viral populations isolated from hosts in different continents were genetically similar. According to the authors, the findings uncover a high level of genomic diversity in HCMV populations, and may inform the development of effective therapeutics. — A.G.
Carbon recycling into deep mantle at subduction zones
At subduction zones, one tectonic plate slides beneath the edge of an adjacent plate. Subduction recycles Earth’s uppermost rocky layer, or lithosphere, as the material sinks into the deep mantle, warms, and disaggregates. Seeking to determine the quantity of carbon that subduction returns to Earth’s deep interior, Peter Kelemen and Craig Manning (pp. E3997–E4006) reevaluated key carbon reservoirs and transport mechanisms associated with the process. In contrast to previous studies, which found that about half the subducting carbon returns to the deep mantle, the authors determined that little recycling of carbon may occur. Instead, most subducting carbon is returned to the lithosphere, the atmosphere, and the oceans within 5–10 million years. Furthermore, the authors report, if the subduction zone carbon cycle is approximately balanced, outgassing from midocean ridges and within-plate volcanism represents a net flux from the deep mantle to Earth’s surface, and the carbon content of the lithosphere has increased over Earth’s history. According to the authors, the high degree of uncertainty in the estimates suggest that the latter possibility is broadly consistent with data on the carbon content of the continents, noble gas tracer studies, and recycled carbon in mantle diamonds. — T.J.
Measuring aging in young adults
Pace of aging was measured by tracking changes in 18 biomarkers. Image courtesy of BioDigital (www.biodigital.com).
The burden of age-related disease and disability rises as the global population ages, prompting a need for antiaging interventions. Such interventions should be implemented before disease and disability develop, but there are currently no reliable methods to measure the progress of aging in young adults. Daniel Belsky et al. (pp. E4104–E4110) examined 954 individuals from the Dunedin Study birth cohort, a representative sample of individuals born in 1972–1973 and followed to the age of 38 years. The authors calculated the participants’ biological age, a measure of aging developed using the US National Health and Nutrition Survey. Despite all of the participants being 38 years of age, their biological ages varied from 28–61 years. The authors also quantified the participants’ paces of aging from changes in 18 different biomarkers between ages 26 and 38. Compared with their slow-aging peers, fast-aging participants showed reduced balance, motor control, and grip strength as well as greater IQ declines from childhood and signs of increased stroke and dementia risk. Fast-aging individuals also reported worse health and appeared older to independent observers than slow-aging individuals. The results suggest that it may be possible to quantify differences in aging in young individuals, potentially enabling tests of the effectiveness of antiaging therapies. — B.D.
Dichromacy and color preference
Colorful flowers as seen in trichromat vision (Left) and in dichromat simulation (Right).
Around 2% of human males have dichromacy, a color vision deficiency in which one type of cone photoreceptor is missing. Leticia Álvaro et al. (pp. 9316–9321) examined 32 individuals with normal color vision, trichromats, and 32 individuals lacking either L (red) or M (green) cones, dichromats, to determine how dichromacy affects individuals’ color preferences. Trichromats showed high preference for blue hues and low preference for yellow–green hues, in agreement with previous research. In contrast, dichromats showed high preference for yellow hues and low preference for cyan and red hues. Trichromats distinguish color through two mechanisms: the difference between L and M cone responses (red–green), and the difference between S and L+M cone responses (yellow–blue). The authors calculated the cone responses for each color relative to its background and found that color preference in trichromats correlated strongly with the yellow–blue mechanism. In dichromats, preference correlated with the absolute value of the yellow–blue mechanism. The authors also determined how quickly, accurately, and consistently individuals could name each color, and found that both male dichromats and male trichromats typically preferred colors that could be rapidly and accurately named. The results provide insight into how dichromats experience color and why some colors are preferred over others, with implications for general theories of aesthetics, according to the authors. — B.D.