Linking Nuclear Mechanotransduction and Epigenetics in Morphogenesis

Student: Kellin Fenelon

Supervisor: Dr. Sevan Hopyan

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Meeting ID: 926 3485 9116

Passcode: 207224

Abstract

Organ primordia shape is important for pattern formation and organ function. Morphogenesis generates forces through cellular rearrangements, proliferation, and shape change. These forces are felt by the cells of each tissue and are transmitted through them via the cytoskeleton. In addition to shaping tissues during development, emerging research suggests that mechanical forces play a role in gene expression. A traditional view of mechanotransduction is that extracellular and intracellular forces elicit a biochemical response, transmitting information to the nucleus. Intriguingly, evidence in vitro shows that nuclear strain can mechanically influence transcription by deforming the chromatin. Forces transmitted from the cytoskeleton to the nuclear lamina via the LINC complex, a direct mechanical connection, have the potential to efficiently couple morphogenesis with gene expression by pulling the genome to activate genome topology sensitive genes like the HoxA/HoxD clusters. To facilitate the investigation of potential nuclear mechanotransduction in vivo, I generated transgenic FRET‐based tension sensors. I utilized these sensors within the LINC complex protein, Nesprin2G, which links actin to SUN proteins, and the inner nuclear membrane protein NEMP1 which joins the nuclear lamina to chromatin to measure nuclear force transmission in living tissues. I tested in vivo the responsiveness of each conditionally expressed sensor to physical and chemical manipulation of the mouse embryo. I helped develop software (FLIMvivo) to resolve challenges uniquely abundant in in vivo fluorescence lifetime imaging analysis. I found that force transmission to the nuclear interior indeed varies by tissue in the developing forelimb. Further, I used exogenous force via atomic force microscopy to modulate HoxA expression in live embryo forelimbs and have adapted a recently developed 3D stochastic reconstruction microscopy (3D‐STORM) OligoPaint approach to enable super resolution acquisition of chromatin topology at the single gene locus scale under differing cellular force regimes. These tools will be useful to measure the extent to which the genome and gene expression are influenced directly by the forces felt by cells not only during limb bud development, but also in other developmental processes, cancer, and disease.