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Mechanobiology of Disease
Poster Abstracts
84
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.