Biophysical Society Thematic Meeting | Singapore

Mechanobiology of Disease

Poster Abstracts

38-POS Board 38 A Mechano-transduction in Zebrafish Heart Development Atsushi Kubo 1 , Takahiro Niida 1 , Daisuke Yoshino 2 , Kota Miyasaka 1 , Yusuke Watanabe 1 , Toshihiko Ogura 1 . 1 Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi, Japan, 2 Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan. The physical forces are regarded as new important signals for development and homeostasis. In zebrafish heart, mechanical stresses evoked by blood flow (eg. shear and stretch stresses) play essential roles during morphogenesis of heart (Nature 421, 172, 2003, Nature Communications 4, 1978, 2013). Nonetheless, molecular mechanisms and functional links between mechanical forces and transcriptional control of genes remain largely unknown. In this study, we focused on the transcriptional co-activator, mkl2 , since we found that this co- activator plays an important role during mechano-transduction pathway. We carried out an in vitro stretch assay to apply mechanical stresses to cardiac myoblast cells, H9C2. H9C2 cells stably expressing flag-tagged mkl2 were seeded on an elastic chamber and subjected to cyclic stretch. Soon after a short period of stretching, nuclear localization of mkl2 increased at the expense of cytoplasmic localization, indicating a rapid nuclear shuttling of mkl2. When we overexpressed an actin mutant S14C that enhances actin polymerization, again, nuclear accumulation of mkl2 was observed, suggesting that the stretch-induced nuclear translocation of mkl2 is mediated by the actin polymerization. mkl2 -deficient zebrafish embryos generated by Morpholino antisense oligos (MO) or the CRISPR/Cas9 system showed severe heart defects. To analyze relationship between the mechanical forces and mkl2 translocation, we first visualized actin dynamics in the transgenic embryos that express Lifeact-eGFP. At 24 hours post fertilization (hpf), contraction of heart was still very weak, and no polymerized signal of actin was detected. However, at 72 hpf, the heart contracts strongly, and highly polymerized actin meshwork was evident at this time point. This actin polymerization was disappeared when cardiac contraction was arrested by BDM or injection of MO against tnnt2 . These results indicate that heartbeat promotes polymerization of actin, which is indispensable for nuclear shuttling of mkl2 in zebrafish embryos.

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