This Week in PNAS
ANTHROPOLOGY
Teeth and rainfall influence primate reproductive success
Stephen King et al. report that the amount of rainfall during the lactation season limits the reproductive success of aging female lemurs, and tooth wear may play a role. Primate teeth wear down over time, impacting nutritional status and potentially reproductive success. To determine how tooth wear influences reproductive success, King et al. documented tooth wear in a population of Madagascar rainforest lemurs, or sifakas, over the past 20 years. The researchers took dental casts of the sifakas' mouths and analyzed tooth wear in three dimensions by using Geographical Information Systems technology. Young sifaka crowns were found to wear down to minimal relief by 6 years of age. The appearance of shearing blades appeared to compensate for the crown flattening, but by 18 years of age, teeth were shown to be essentially worn flat. Despite this loss of dental function, some sifakas were able to survive and produce healthy offspring for another 10 years, as long as rainfall was abundant during the nursing season. This link between tooth wear and rainfall suggests that long-lived mammals may be particularly sensitive to changing environmental conditions. — M.M.
Sifaka tooth wear.
“Dental senescence in a long-lived primate links infant survival to rainfall” by Stephen J. King, Summer J. Arrigo-Nelson, Sharon T. Pochron, Gina M. Semprebon, Laurie R. Godfrey, Patricia C. Wright, and Jukka Jernvall (see pages 16579–16583)
CELL BIOLOGY
Age-related nuclear architecture changes in C. elegans
Erin Haithcock et al. demonstrate that normal Caenorhabditis elegans cells undergo changes in nuclear architecture as they age, changes that are similar to those observed in Hutchinson–Gilford Progeria Syndrome (HGPS). Using GFP-tagged Ce-lamin, the authors monitored worms from larval stages until death for signs of any nuclear morphology changes. Whereas neuronal nuclei showed little change, other cell types developed nuclei with increased intranuclear and decreased peripheral lamin, as well as nuclei with abnormal shape and/or extensive stretching and fragmentation. In addition, aging decreased peripheral heterochromatin levels and altered the distribution of nuclear membrane proteins, such as Ce-emerin and NPP-1. These morphology changes were influenced by the insulin/IGF-1-like signaling pathway, which plays a major role in regulating lifespan. Short-lived or long-lived insulin/IGF-1 mutants had faster or slower rates of change, respectively. Also, reducing the level of Ce-lamin significantly shortened the lifespan of C. elegans. Because HGPS cells display similar architecture changes and are caused by mutations in lamin, these results suggest that HGPS is an acceleration of the normal aging process and that the nucleus is a focal point in regulating aging. — N.Z.
Hypodermal nucleus in 12-day-old C. elegans labeled with Ce-lamin::GFP.
“Age-related changes of nuclear architecture in Caenorhabditis elegans” by Erin Haithcock, Yaron Dayani, Ester Neufeld, Adam J. Zahand, Naomi Feinstein, Anna Mattout, Yosef Gruenbaum, and Jun Liu (see pages 16690–16695)
NEUROSCIENCE
Gain-of-function mutations in Parkinson's disease
Andrew West et al. report that mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause an increase in LRRK2 phosphorylation activity in Parkinson's disease. Previous research has identified two mutations in LRRK2, G2019S and R1441C, in patients with familial or late-onset Parkinson's disease. West et al. cloned the predominant LRRK2 transcript from human brain tissue and expressed the LRRK2 protein. LRRK2 was found to be present in cellular cytosol and the outer membrane of the mitochondria. The familial-linked G2019S- and R1441C-LRRK2 mutant proteins were found to be expressed in a similar pattern in cells, with similar turnover rates compared with wild-type LRRK2 protein. In vitro kinase activity assays demonstrated that the G2019S mutant phosphorylated myelin basic protein at a significantly greater rate than LRRK2. In addition, both mutant familial-linked LRRK2 proteins exhibited greater autophosphorylation activity than wild-type LRRK2 in the absence of cofactors or activators. These findings suggest a mechanism of gain-of-function kinase activity of familial-linked LRRK2 mutations in the development of Parkinson's disease. — F.A.
G2019S mutation of LRRK2 potentiates kinase activity.
“Parkinson's disease-associated mutations in leucine-rich repeat kinase 2 augment kinase activity” by Andrew B. West, Darren J. Moore, Saskia Biskup, Artem Bugayenko, Wanli W. Smith, Christopher A. Ross, Valina L. Dawson, and Ted M. Dawson (see pages 16842–16847)
NEUROSCIENCE
Bees distinguish complex color scenes
According to research by Beau Lotto and Martina Wicklein, bumblebees generate color-constant behavior even in complex scenes with multiple types of illumination. Although bees are known to discriminate colors under global illumination changes, it has not been known whether they can solve more complex visual challenges, such as dappled light across a woodland floor. Lotto and Wicklein trained visually naïve bumblebees (Bombus terrestris) to find artificial Plexiglas flowers of a particular color using a food reward. The bees' ability to find the same color was measured in scenes simultaneously lit by four different types of illumination (UV/yellow, blue, yellow, and green ambient light), conditions far more constrained in terms of stimulus information than those experienced in nature. The bees were able to identify the rewarded flowers under these color conditions, even when one of the illuminated regions was changed to a color the bees had never experienced. This finding suggests that bees have more sophisticated color vision than previously thought, and such knowledge might help elucidate how the human eye discriminates color in similar situations. — M.M.
Illuminated artificial flower and bumblebee.
“Bees encode behaviorally significant spectral relationships in complex scenes to resolve stimulus ambiguity” by R. Beau Lotto and Martina Wicklein (see pages 16870–16874)
PLANT BIOLOGY
Cyclic electron flow feeds C4 photosynthesis
Atsushi Takabayashi et al. identify a cyclic electron flow pathway as a major source of the extra energy required by C4 plants, such as corn. C4 plants have evolved a special carbon dioxide concentration mechanism that allows plants in hot, dry climates to prevent water loss. However, C4 photosynthesis requires two more molecules of ATP compared with C3 photosynthesis. The source of this extra ATP has remained unclear, although cyclic electron flow (CEF), which produces only ATP, has been a suspected candidate. To determine how CEF contributes to the additional ATP requirement, Takabayashi et al. measured the amounts of two enzymes (NDH and PGR5) that represent alternative pathways of CEF. NDH and PGR5 levels were assessed in four types of C4 plant cells requiring a high level of ATP synthesis. High levels of NDH but very low levels of PGR5 were found in these cells, suggesting that CEF via NDH is a major source of ATP generation in these plants. The results demonstrate how C4 plants, which include many important crop species, have adapted to stressful conditions and may provide a molecular target for improving drought tolerance via genetic engineering. — M.M.
Schematic model of ATP production.
“Differential use of two cyclic electron flows around photosystem I for driving CO2-concentration mechanism in C4 photosynthesis” by Atsushi Takabayashi, Masahiro Kishine, Kozi Asada, Tsuyoshi Endo, and Fumihiko Sato (see pages 16898–16903)
