Biology subjects

Sivan, E.

Publications and source records attributed to Sivan, E..

3 recordsLinked to original sources

bioRxiv2024

The Natural Material Evolution and Stage-wise Assembly of Silk Along the Silk Gland

Silk fibers, with their highly ordered structure and mechanically superb properties, are produced in arthropod glands at minimal energy input and ambient conditions, a remarkable feat yet to be achieved synthetically. Due to the high instability and shear sensitivity of the silk protein feedstock, understanding silk fiber formation has been largely limited to in-vitro studies of certain gland sections, offering only a fragmented view of this process. Here, we monitor the whole silk feedstock processing in-situ, at the nano- to micron-scales, through imaging its progressive macromolecular assemblies and phase transitions along the entire Bombyx mori silkworm silk gland. This is done by combining state-of-the-art microscopy techniques, such as cryogenic sample preparation, fixation, and imaging. Our work reveals that fibroin assembles into micron-sized spherical storage "compartments" in the posterior and middle gland sections, a state that ensures its stability and avoids premature fibrillation. These compartments undergo several structural transformations along the gland and eventually disassemble at the entry to the anterior section, before the silk feedstock spinning begins. The spinning itself commences via a series of structural transitions, from the alignment of protein chains in liquid feedstock, through the formation of several fibrillated nano-structures and, in the final stage, a network of cross-linked nano-bundles, which determines the structure and properties of the final microfiber. Importantly, the length of the anterior section of the silk gland enables such gradual and balanced structural transitions. This direct imaging of silks natural formation process can help formulate a template for the transformation of fibrillar proteins into synthetic bio-fibers. DedicationThis work is dedicated to the memory of Dr. Eyal Shimoni, who was a valued colleague and a dear friend. Eyal was a vital part of this research and was essential in shaping its direction. He will be deeply missed for his intellect, mindfulness, creativity, and unwavering dedication to scientific development. Though he is no longer with us, his influence and spirit continue to inspire us in our scientific pursuits. May his passion for discovery and commitment to excellence live on through this work.

biochemistry↗

bioRxiv2023

High-energy demand and nutrient exhaustion in MTCH2 knockout cells

Mitochondrial carrier homolog 2 (MTCH2) is a regulator of apoptosis, mitochondrial dynamics, and metabolism. Loss of MTCH2 results in mitochondrial fragmentation, an increase in whole-body energy utilization, and protection from diet-induced obesity. We now show using temporal metabolomics that MTCH2 deletion results in a high ATP demand, an oxidized environment, a high lipid/amino acid/carbohydrate metabolism, and in the decrease of many metabolites. Lipidomics analyses show a strategic adaptive decrease in membrane lipids and an increase in storage lipids in MTCH2 knockout cells. Importantly, all the metabolic changes in the MTCH2 knockout cells were rescued by MTCH2 re-expression. Interestingly, this imbalance in energy metabolism and reductive potential triggered by MTCH2-deletion inhibits adipocyte differentiation, an energy consuming reductive biosynthetic process. In summary, loss of MTCH2 results in an increase in energy demand that triggers a catabolic and oxidizing environment, which fails to fuel the anabolic processes during adipocyte differentiation.

cell biology↗

bioRxiv2023

Egg MVBs elicit an antimicrobial pathway to degrade paternal mitochondria after fertilization

Mitochondria are maternally inherited, but the mechanisms underlying paternal mitochondrial elimination (PME) after fertilization are far less clear. Using Drosophila, we show that special egg-derived multivesicular bodies (MVBs) promote PME by activating LC3-associated phagocytosis (LAP), a cellular defense pathway commonly employed against invading microbes. Upon fertilization, the egg MVBs engage and densely coat the sperm flagellum, forming extended flagellum vesicular sheaths (FVSs), within which the paternal mitochondria degrade. Inactivation of multiple LAP pathway components, such as Rubicon, a LAP-specific class III PI(3)K complex protein, significantly attenuates PME. Furthermore, recruitment of Atg8/LC3 to the FVS requires both Rubicon and the Atg8/LC3 conjugation machinery. Other LAP pathway events, such as production of the phospholipid PtdIns(3)P and reactive oxygen species (ROS), also unfold during PME. Finally, we provide evidence that a similar pathway might also mediate PME in mammals, highlighting the notion that eggs may regard paternal mitochondria as potentially dangerous trespassers.

developmental biology↗