Presenting Author:

Patrick Liu

Principal Investigator:

John Marko

Department:

Cell and Molecular Biology

Keywords:

Nuclear morphology, blebbing, chromatin compaction, euchromatin, heterochromatin, progeria, lamina

Location:

Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital

B21 - Basic Science

Nuclear Blebbing Solely as a Function of Chromatin Compaction State

The nucleus houses the genome and is critical for regulating its functional organization. Classically, in mammalian nuclei, the compact, transcriptionally silent heterochromatin is docked to the lamina network at the periphery, thereby providing mechanical support to the nucleus. In many human diseases, such as progeria, cancers, and muscular dystrophies, nuclear morphology becomes severely altered and demonstrates blebbing as a result of impaired nuclear rigidity stemming from disruptions to chromatin compaction and lamina content. To elucidate chromatin’s individual role in contributing to the formation of pathologically misshapen nuclei, we show that decompacting chromatin via histone deacetylase inhibitor (HDACi) treatment alone is sufficient to induce nuclear blebbing. Through immunofluorescence imaging via confocal microscopy, we demonstrate that treating mouse embryonic fibroblasts with HDACi decompacts chromatin, relocates euchromatin to the periphery, and causes blebbing independent of disruptions to the lamina or actin network. Moreover, the divalent ion magnesium is known to compact chromatin. In accordance with this, we found that increasing extracellular magnesium chloride concentrations rescues nuclear blebbing in a dose-dependent manner, restores heterochromatin signal at the periphery, and significantly increases the heterochromatin signal histone H3 lysine 27 tri-methyl. Moreover, nuclear morphology in HeLa cells expressing progerin, a mutated form of lamin A present in progeria that causes severe nuclear deformities, was also rescued via magnesium chloride treatment. Thus, nuclear blebbing can both be induced and suppressed through solely altering chromatin compaction states. Similarly, a pathological phenotype that stems from a lamina mutation can be rescued through the same chromatin mechanism, thereby suggesting a significant role of chromatin in disease and providing a potential therapeutic target.