לוח שנה משולב

A critical factor determining the biological activities of sphingolipids (SLs) is their N-acyl chain length, which in mammals is determined by a family of six ceramide synthases (CerS). Using site-directed mutagenesis and biochemical analyses, we have found a short sequence in a loop located between the last two putative transmembrane domains (TMDs) of the CerS, determines their acyl-CoA specificity. The specificity of a chimeric protein based on the backbone of CerS5 (which generates C16-ceramide), but containing 11 residues from CerS2 (which generates C22–C24-ceramides), allowed the enzyme to generated C22– C24 and other ceramides. Moreover, a similar chimeric protein based on the backbone of CerS4 (which normally generates C18–C22 ceramides) displayed significant activity toward C24:1-CoA.

Our organs exhibit complex and precise shapes which emerge during embryonic development. While biology has focused on a genetic study of organ formation, we have a limited understanding of the mesoscale mechanical forces which shape organs. A central question is how the physical form of an organ self-organizes from the collective activity of its constituents - thousands of fluctuating microscopic biological cells. Establishing a physical framework for understanding organ shape across scales requires a tight interplay between experiment and theory. However, organ development occurs within the embryo, an extraordinarily complex and coupled system with limited experimental access. To address this challenge, we developed a minimal quantitative system to study the dynamics of organ shape formation in a dish. By combining materials science with stem-cell research tools, we recreated the formation of the human neural tube - the first milestone in brain development. Experiments and vertex-model simulations reveal that a wetting transition can explain the complex dynamics of neural tube formation. Our approach paves the way for a predictive understanding of human organ formation in health and disease.

When Hanbury-Brown and Twiss proposed to use photon correlations for stellar interferometry in 1954 the idea was received with great skepticism. Yet, the use of photon correlations for various uses, from identification of quantum emitters to emitter counting grew over the years. In the talk, I will describe some of our efforts in using HBT correlations and their derivatives in superresolution microscopy and in advanced spectroscopy of quantum emitters, as well as the technological advances enabling this.

Diatoms are among the most globally distributed and ecologically successful organisms in the modern ocean, contributing upwards of 40% of total marine primary productivity. Diatom production is tightly coupled with carbon export through the ballasted nature of the silica-based cell wall, linking the oceanic silicon and carbon cycles. While viruses are considered key players in ocean biogeochemical cycles, little is known about how viral infection specifically impacts diatom populations. Using a suite of molecular, physiological and geochemical approaches, we explored diatoms and associated viruses across diverse nutrient regimes in the northeast Pacific. We found that silicon (Si) limitation facilitated virus infection and mortality in diatoms while the onset of iron (Fe) limitation, in sharp contrast, substantially reduced viral replication. These findings, recapitulated in model systems, suggest that virus-mediated mortality in Si-limited regimes would facilitate diatom remineralization in the surface ocean, while diatoms in Fe-limited regimes may escape viral lysis, ultimately contributing to carbon export. We also explored how viral infection of diatoms might impact the microbial processing of organic matter in the ocean. Using bacterial isolates and model diatom host-virus systems, we tested how bacteria respond to dissolved organic matter generated during viral infection in diatoms. We found that this material can significantly stimulate ectoproteolytic activity, implicating viral infection of diatoms in bacteria-mediated recycling of organic matter and silica in the surface ocean. Together, these findings highlight the dynamic role that diatom host–virus interactions play in shaping the biogeochemical landscape the global ocean.