Walrasian equilibrium behavior in nature

The interaction between land plants and mycorrhizal fungi (MF) forms perhaps the world’s most prevalent biological market. Most plants participate in such markets, in which MF collect nutrients from the soil and trade them with host plants in exchange for carbon. In a recent study, M. D. Whiteside et al. [Curr. Biol. 29, 2043–2050.e8 (2019)] conducted experiments that allowed them to quantify the behavior of arbuscular MF when trading phosphorus with their host roots. Their experimental techniques enabled the researchers to infer the quantities traded under multiple scenarios involving different amounts of phosphorus resources initially held by different MF patches. We use these observations to confirm a revealed preference hypothesis, which characterizes behavior in Walrasian equilibrium, a centerpiece of general economic equilibrium theory.

Sleep-learning Impairs Subsequent Awake-learning

Although we can learn new information while asleep, we cannot consciously remember the sleep-formed memories because learning occurred in an unconscious state. Here, we ask whether sleep-learning expedites the subsequent awake-learning of the same information. To answer this question, we reanalyzed data (Züst et al., 2019, Curr Biol) from napping participants, who learned new semantic associations between fake foreign-words and translation-words (guga-ship) while in slow-wave sleep. They retrieved sleep-formed associations unconsciously on an implicit memory test following awakening. Then, participants took five runs of paired-associative learning to probe carry-over effects of sleep-learning on awake-learning. Surprisingly, sleep-learning diminished awake-learning when participants learned semantic associations that were congruent to sleep-learned associations (guga-boat). Yet, learning associations that conflicted with sleep-learned associations (guga-coin) was unimpaired relative to learning new associations (resun-table; baseline). We speculate that the impeded wake-learning originated in a deficient synaptic downscaling and resulting synaptic saturation in neurons that were activated during both sleep-learning and awake-learning.

Mixed-polarity random-dot stereograms alter GABA and Glx concentration in the early visual cortex

The offset between images projected onto the left and right retina (binocular disparity) provides a powerful cue to the three-dimensional structure of the environment. It was previously shown that depth judgements are better when images comprise both light and dark features, rather than only light or only dark elements. Since Harris and Parker ( Nature 374: 808–811, 1995) discovered the “mixed-polarity benefit,” there has been limited evidence supporting their hypothesis that the benefit is due to separate bright and dark channels. Goncalves and Welchman ( Curr Biol 27: 1403–1412, 2017) observed that single- and mixed-polarity stereograms evoke different levels of positive and negative activity in a deep neural network trained on natural images to make depth judgements, which also showed the mixed-polarity benefit. Motivated by this discovery, we seek to test the potential for changes in the balance of excitation and inhibition that are produced by viewing these stimuli. In particular, we use magnetic resonance spectroscopy to measure Glx and GABA concentrations in the early visual cortex of adult humans during viewing of single- and mixed-polarity random-dot stereograms (RDS). We find that participants’ Glx concentration is significantly higher, whereas GABA concentration is significantly lower, when mixed-polarity RDS are viewed than when single-polarity RDS are viewed. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents, consistent with recent theoretical work (Goncalves NR, Welchman AE. Curr Biol 27: 1403–1412, 2017). NEW & NOTEWORTHY Depth judgements are better when images comprise both light and dark features, rather than only light or only dark elements. Using magnetic resonance spectroscopy, we show that adult human participants’ Glx concentration is significantly higher whereas GABA concentration is significantly lower in the early visual cortex when participants view mixed-polarity random-dot stereograms (RDS) compared with single-polarity RDS. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents.

Crystal structure of diaphorin methanol monosolvate isolated from Diaphorina citri Kuwayama, the insect vector of citrus greening disease

The title compound C22H39NO9·CH3OH [systematic name: (S)-N-((S)-{(2S,4R,6R)-6-[(S)-2,3-dihydroxypropyl]-4-hydroxy-5,5-dimethyltetrahydro-2H-pyran-2-yl}(hydroxy)methyl)-2-hydroxy-2-[(2R,5R,6R)-2-methoxy-5,6-dimethyl-4-methylenetetrahydro-2H-pyran-2-yl]acetamide methanol monosolvate], was isolated from the Asian citrus psyllid, Diaphorina citri Kuwayama, and crystallizes in the space group P21. `Candidatus Profftella armatura' a bacterial endosymbiont of D. citri, biosynthesizes diaphorin, which is a hybrid polyketide–nonribosomal peptide comprising two highly substituted tetrahydropyran rings joined by an N-acyl aminal bridge [Nakabachi et al. (2013). Curr. Biol. 23, 1478–1484]. The crystal structure of the title compound establishes the complete relative configuration of diaphorin, which agrees at all nine chiral centers with the structure of the methanol monosolvate of the di-p-bromobenzoate derivative of pederin, a biogenically related compound whose crystal structure was reported previously [Furusaki et al. (1968). Tetrahedron Lett. 9, 6301–6304]. Thus, the absolute configuration of diaphorin is proposed by analogy to that of pederin.

Memory-guided saccades show effect of a perceptual illusion whereas visually guided saccades do not

The double-drift stimulus (a drifting Gabor with orthogonal internal motion) generates a large discrepancy between its physical and perceived path. Surprisingly, saccades directed to the double-drift stimulus land along the physical, and not perceived, path (Lisi M, Cavanagh P. Curr Biol 25: 2535−2540, 2015). We asked whether memory-guided saccades exhibited the same dissociation from perception. Participants were asked to keep their gaze centered on a fixation dot while the double-drift stimulus moved back and forth on a linear path in the periphery. The offset of the fixation was the go signal to make a saccade to the target. In the visually guided saccade condition, the Gabor kept moving on its trajectory after the go signal but was removed once the saccade began. In the memory conditions, the Gabor disappeared before or at the same time as the go-signal (0- to 1,000-ms delay) and participants made a saccade to its remembered location. The results showed that visually guided saccades again targeted the physical rather than the perceived location. However, memory saccades, even with 0-ms delay, had landing positions shifted toward the perceived location. Our result shows that memory- and visually guided saccades are based on different spatial information. NEW & NOTEWORTHY We compared the effect of a perceptual illusion on two types of saccades, visually guided vs. memory-guided saccades, and found that whereas visually guided saccades were almost unaffected by the perceptual illusion, memory-guided saccades exhibited a strong effect of the illusion. Our result is the first evidence in the literature to show that visually and memory-guided saccades use different spatial representations.

Sleep and memory consolidation: a common mechanism across species?

In humans, memory consolidation can be aided by the representation of an odor previously associated with target information during sleep. In an elegant study, Zwaka et al. ( Curr Biol 25: 2869–2874, 2015) have demonstrated that the same process occurs in honeybees, suggesting that the relationship between sleep and memory may be similar across different animal species.

110 COMPARATIVE ANALYSIS OF DNA AND HISTONE H3 METHYLATION REPROGRAMMING IN MOUSE, BOVINE, AND RABBIT ZYGOTES

Active demethylation of paternal DNA in zygotes has been documented for many mammalian species, including mouse (Mayer et al. 2000 Nature 403, 501–505), rat (Zaitseva et al. 2007 Mol. Reprod. Dev. 74, 1255–1261), pig (Fulka et al. 2006 Histochem. Cell. Biol. 126, 213–217), Homo sapiens (Fulka et al. 2004 Reproduction 128, 703–708), and cow (Beaujean et al. 2004 Curr. Biol. 14, 266–267). The generality of this concept has been challenged by reports stating that there is no detectable genome-wide paternal DNA demethylation in rabbit (Shi et al. 2004 Biol. Reprod. 71, 340–347) and ovine (Beaujean et al. 2004 Curr. Biol. 14, 266–267), whereas others report partial evidence for the opposite (Zhang et al. 2005 Mol. Reprod. Dev. 72, 530–533). In order to compare the fate of DNA and histone H3 methylation (H3/K4triMe and H3/K9diMe), we performed studies on mouse, bovine, and rabbit zygotes using specific antibodies in an indirect immunofluorescence approach. We observed a similar distribution of these epigenetic modifications in maternal and paternal pronuclei of the zygote, indicating that the overall epigenetic reprogramming activities — including the DNA demethylation of the paternal pronucleus — are conserved between mammalian species. For all 3 species we found a clear asymmetry in mouse monoclonal antimethylcytosine (MeC) antibody signal intensities between paternal and maternal pronuclei at advanced stages, which suggests the presence of paternal DNA demethylation. To obtain additional evidence for the presence of DNA demethylation activity in rabbit zygotes, we examined 1-cell embryos after somatic cell nuclear transfer (SCNT) using rabbit fetal fibroblasts as nuclear donors, and we found a strong signal reduction in SCNT embryos 4 h after activation. For the majority of SCNT 1-cell embryos, we estimated at least a 4- to 6-fold decrease of MeC signal. Along with the similarities of DNA demethylation kinetics in rabbit, mouse, and bovine zygotes, we found a conserved distribution of H3/K4triMe and H3/K9diMe signals on maternal and paternal chromatin. In all 3 species, H3/K4triMe, which predominantly demarcate open chromatin, is present in both pronuclear chromatin, whereas H3/K9diMe, a hallmark of condensed chromatin, is strongly enriched in maternal pronuclear chromatin and undetectable in paternal chromatin. Furthermore, we observed a similar asymmetric compartmentalization of paternal and maternal chromosomes in early 2-cell rabbit and bovine embryos as monitored by H3/K9diMe, which marks maternally derived chromosomes. In summary, our data suggest that mechanisms of epigenetic reprogramming are conserved in mammalian species both on the level of DNA and chromatin methylation.

Growth control by EGF repeats of the C. elegans Fibulin-1C isoform

Fibulin is a broadly conserved component of the extracellular matrix (ECM). Previous studies have shown that Caenorhabditis elegans FIBULIN-1 (FBL-1) controls the width of the gonad (Hesselson, D., C. Newman, K.W. Kim, and J. Kimble. 2004. Curr. Biol. 14:2005–2010; Kubota, Y., R. Kuroki, and K. Nishiwaki. 2004. Curr. Biol. 14:2011–2018; Muriel, J.M., C. Dong, H. Hutter, and B.E. Vogel. 2005. Development. 132: 4223–4234). In this study, we report that FBL-1 also controls developmental growth and that one isoform of fibulin-1, called FBL-1C, controls both functions by distinct mechanisms. A large FBL-1C fragment, including both epidermal growth factor (EGF) and fibulin-type C domains, is responsible for constraining gonadal width, but a much smaller fragment containing only two complete EGF repeats (EGF1-2C+) is critical for developmental growth. We suggest that the larger fragment serves a scaffolding function to stabilize the basement membrane and that the smaller fragment provides a regulatory function at the cell surface or within the ECM to control growth.

Chfr acts with the p38 stress kinases to block entry to mitosis in mammalian cells

Entry into mitosis in vertebrate cells is guarded by a checkpoint that can be activated by a variety of insults, including chromosomal damage and disrupting microtubules (Rieder, C.L., and R.W. Cole. 1998. J. Cell Biol. 142:1013–1022; Rieder, C.L., and R.W. Cole. 2000. Curr. Biol. 10:1067–1070). This checkpoint acts at the end of interphase to delay cells from entering mitosis, causing cells in prophase to decondense their chromosomes and return to G2 phase. Here, we show that in response to microtubule poisons this “antephase” checkpoint is primarily mediated by the p38 stress kinases and requires the Chfr protein that is absent or inactive in several transformed cell lines (Scolnick, D.M., and T.D. Halazonetis. 2000. Nature. 406:430–435) and lung tumors (Mizuno, K., H. Osada, H. Konishi, Y. Tatematsu, Y. Yatabe, T. Mitsudomi, Y. Fujii, and T. Takahashi. 2002. Oncogene. 21:2328–2333). Furthermore, in contrast to previous reports, we find that the checkpoint requires ubiquitylation but not proteasome activity, which is in agreement with the recent demonstration that Chfr conjugates ubiquitin through lysine 63 and not lysine 48 (Bothos, J., M.K. Summers, M. Venere, D.M. Scolnick, and T.D. Halazonetis. 2003. Oncogene. 22:7101–7107).