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Fig. 4 fibronectin 1 expression is regulated by mtx1. fibronectin 1 gene expression and Fibronectin protein localization around the migrating myocardial cells were examined in embryos injected into the YSL with mtx1 MO(A) or mtx1 mRNA. (A-F) Anterior views, (G,H) Lateral views in the head region. (A-H) fibronectin 1 expression at the 14-(A,B; 16 hpf), 18-(E-H; 18 hpf), and 21-somite stages (C,D; 21.5 hpf). (A-D) fibronectin 1 expression appeared to be reduced in mtx1 MO(A)-injected embryos. (E-H) Conversely, fibronectin 1 expression appeared to be increased in mtx1 mRNA-injected embryos. (F,H) fibronectin 1 expression was upregulated mostly in embryonic tissues, even though mtx1 mRNA was injected into the YSL (red dots in H), indicating that mtx1 regulates fibronectin 1 expression in a non-cell-autonomous manner. (I-K) Transverse sections of cmlc2:GFP (false colored blue) transgenic embryos immunostained for β-catenin (red) and Fibronectin (green). Fibronectin deposition appeared to be decreased in mtx1 MO-injected embryos (J), whereas it appeared to be increased in mtx1 mRNA-injected embryos (K) specifically in embryonic tissues.