Michelle Nunez-Garcia giving a great lecture on the benefits between Widefield microscopy and Laser Scanning Confocal

by Heidi Hehnly in , ,


Michelle, an undergraduate in our lab, gave a great lecture this past week on the pluses and minuses of widefield and laser scanning confocal microscopy in our graduate level course at SU on Microscopy Techniques in Cell Biology. She presented one of my favorite papers by Jason Swedlow that really digs into the advantages of widefield imaging with deconvolution for resolving dim fluorescent structures in live samples. The paper was titled “Measuring tubulin content in Toxoplasma gondii: A comparison of laser-scanning confocal and wide-field fluorescence microscopy” and can be found here.

Michelle presenting on Widefield Microscopy with deconvolution using the model organism Toxoplasma Gondii.

Michelle presenting on Widefield Microscopy with deconvolution using the model organism Toxoplasma Gondii.


Congrats to Lindsay Rathbun and what a fun IZFC!

by Heidi Hehnly in , , ,


Lindsay won 3rd place at the International Zebrafish Conference (IZFC) this past week in Madison Wisconsin.  We had a great time visiting friends, learning about zebrafish, and presenting our work.  Lindsay also gave an oral presentation on her and Erica Colicino's studies testing the role of the cytokinetic bridge in lumen formation.  Great Job Lindsay! I can't wait to go next year to the IZFC! Also, my favorite conference companion Bart Hehnly Chang also had a successful flight and Madison trip!


Check out the new Castaneda Lab Paper that we assisted with!

by Heidi Hehnly in ,


Under stress, certain eukaryotic proteins and RNA assemble to form membraneless organelles known as stress granules. The most well-studied stress granule components are RNA-binding proteins that undergo liquid-liquid phase separation (LLPS) into protein-rich droplets mediated by intrinsically disordered low-complexity domains (LCDs). Here we show that stress granules include proteasomal shuttle factor UBQLN2, an LCD-containing protein structurally and functionally distinct from RNA-binding proteins.  In vitro , UBQLN2 exhibits LLPS at physiological conditions. Deletion studies correlate oligomerization with UBQLN2’s ability to phase-separate and form stress-induced cytoplasmic puncta in cells. Using nuclear magnetic resonance (NMR) spectroscopy, we mapped weak, multivalent interactions that promote UBQLN2 oligomerization and LLPS. Ubiquitin or polyubiquitin binding, obligatory for UBQLN2’s biological functions, eliminates UBQLN2 LLPS, thus serving as a switch between droplet and disperse phases. We postulate that UBQLN2 LLPS enables its recruitment to stress granules, where its interactions with ubiquitinated substrates reverse LLPS to enable shuttling of clients out of stress granules.

Under stress, certain eukaryotic proteins and RNA assemble to form membraneless organelles known as stress granules. The most well-studied stress granule components are RNA-binding proteins that undergo liquid-liquid phase separation (LLPS) into protein-rich droplets mediated by intrinsically disordered low-complexity domains (LCDs). Here we show that stress granules include proteasomal shuttle factor UBQLN2, an LCD-containing protein structurally and functionally distinct from RNA-binding proteins. In vitro, UBQLN2 exhibits LLPS at physiological conditions. Deletion studies correlate oligomerization with UBQLN2’s ability to phase-separate and form stress-induced cytoplasmic puncta in cells. Using nuclear magnetic resonance (NMR) spectroscopy, we mapped weak, multivalent interactions that promote UBQLN2 oligomerization and LLPS. Ubiquitin or polyubiquitin binding, obligatory for UBQLN2’s biological functions, eliminates UBQLN2 LLPS, thus serving as a switch between droplet and disperse phases. We postulate that UBQLN2 LLPS enables its recruitment to stress granules, where its interactions with ubiquitinated substrates reverse LLPS to enable shuttling of clients out of stress granules.