לוח שנה משולב

Chemical composition and Sr-Nd isotope ratios of sediments from lake Huguangyan Maar and its vicinity are used to infer the hydro-climatic conditions that prevailed during the last Glacial and early- to mid-Holocene periods in South China. Variations in 87Sr/86Sr ratios in the lake sediments indirectly indicate two modes of climate conditions: wet intervals during which the lake sediments are mainly derived from the volcanic-lake rim materials, expressed in low 87Sr/86Sr, and dry intervals during which fine particles from the nearby granitic soils are windblown to the lake and supply local dust with high 87Sr/86Sr ratios to the sediments. These wet and dry intervals generally correspond to regional climate records (e.g., speleothem δ18O profiles in southeast China) and correlate with global climate events, (e.g., Heinrich events). While δ18O records of speleothems from southeast China caves are dominated by the precession signal, the Huguangyan Maar Sr record mainly correlates with obliquity. This most likely reflects masking of the precession signal due to regional climate variability, accentuating the obliquity signal. These local effects may also account for some of the differences that have been observed between the various East Asian monsoon records in the region. More importantly, the masking of the precession signal reveals the influence of obliquity on the hydro-climate regime in South China.

Some animals, especially those living under water use mirrors rather than lenses to form images. Two general strategies exist in nature for forming images using mirrors, exemplified by the concave mirrored eyes of the scallop1 and the reflecting compound eyes of crustaceans2. Here we discuss these two remarkable visual systems and show how the whole hierarchical organization of the mirrors are exquisitely controlled for image-formation from the structure and morphology of the substituent reflecting crystals at the nanoscale to the overall shape of the mirrors at the millimeter scale. Based on our understanding of the optics and structure we can predict what the animal should be seeing. Whether the neural system can integrate all this information, has yet to be determined. From a materials science perspective, understanding how organisms exert such extraord! inary control over the formation and organization of organic crystals provides inspiration for the development of new organic crystalline materials with rationally designed morphologies and properties.
1B.A. Palmer*, G.J. Taylor, V. Brumfeld, D. Gur, M. Shemesh, N. Elad, A. Osherov, D. Oron, S. Weiner, L. Addadi, Science 2017, 358, 1172.
2B.A. Palmer*, A. Hirsch, V. Brumfeld, N. Elad, D. Oron, L. Kronik, L. Leiserowitz, S. Weiner, L. Addadi,* PNAS, 2018, 115, 2299.

Abstract:
I will discuss our work on visualizing “topology atlases” which act as a map of possible circuit designs for small 3-node regulatory motifs. These can help in understanding the relationship between a circuit's structure and its function, but how is this relationship affected if the circuit must perform multiple distinct functions within the same organism? In particular, to what extent do multi‐functional circuits contain modules which reflect the different functions? We computationally surveyed a range of bi‐functional circuits which show no simple structural modularity: They can switch between two qualitatively distinct functions, while both functions depend on all genes of the circuit. Our analysis revealed two distinct classes: hybrid circuits which overlay two simpler mono‐functional sub‐circuits within their circuitry, and emergent circuits, which do not. In this second class, the bi‐functionality emerges from more complex designs which are not fully decomposable into distinct modules and are consequently less intuitive to predict or understand. These non‐intuitive emergent circuits are just as robust as their hybrid counterparts, and we therefore suggest that the common bias toward studying modular systems may hinder our understanding of real biological circuits.

Relevant papers:
1. A spectrum of modularity in multi-functional gene circuits.
Jiménez A, Cotterell J, Munteanu A, Sharpe J. (2017)
Mol Syst Biol 13(4):925. doi: 10.15252/msb.20167347
http://msb.embopress.org/content/13/4/925
2. An atlas of gene regulatory networks reveals multiple three-gene mechanisms for interpreting morphogen gradients.
Cotterell J, Sharpe J. (2010)
Mol Syst Biol 6:425. doi: 10.1038/msb.2010.74
http://msb.embopress.org/content/6/1/425

Bio:
James Sharpe was originally captivated by computer programming, but upon learning about the digital nature of the genetic code, chose to study Biology for his undergraduate degree at Oxford University (1988-1991). He then did his PhD on the genetic control of embryo development at NIMR, London (1992-1997) and in parallel started writing computer simulations of multicellular development. During his post-doc in Edinburgh, he began modelling the dynamics of limb development, and also invented a new optical imaging technology called Optical Projection Tomography (OPT), which is dedicated to imaging specimens too large for microscopy - tissues and organs. In 2006 he moved to Barcelona, becoming a senior group leader at the Centre for Genomic Regulation, and focusing on a systems biology approach to modelling limb development – combining experimentation with computer modelling. In this way the group demonstrated that the signalling proteins which pattern the fingers during embryogenesis, act as a Turing reaction-diffusion system. In 2011 he became the coordinator of the Systems Biology Program, and in 2017 was recruited to EMBL as Head of the new Barcelona outstation on Tissue Biology and Disease Modelling.