Matsui Hiroko, Sakabe Masahide, Sakata Hirokazu, Yanagawa Nariaki, Ikeda Kazuo, Yamagishi Toshiyuki, Nakajima Yuji
Department of Anatomy and Cell Biology, Graduate School of Medicine, Osaka City University, Osaka 545-8585, Japan.
Dev Growth Differ. 2008 Mar;50(3):143-57. doi: 10.1111/j.1440-169X.2008.00987.x. Epub 2008 Feb 27.
During heart development at the gastrula stage, inhibition of bone morphogenetic protein (BMP) activity affects the heart specification but does not impair the expression of smooth muscle alpha-actin (SMA), which is first expressed in the heart mesoderm and recruited into initial heart myofibrils. Interaction of tissues between posterior epiblast and hypoblast at the early blastula stage is necessary to induce the expression of SMA, in which Nodal and Chordin are thought to be involved. Here we investigated the role of fibroblast growth factor-8 (FGF8) in the expression of SMA. In situ hybridization and reverse transcription-polymerase chain reaction showed that Fgf8b is expressed predominantly in the nascent hypoblast. Anti-FGF8b antibody inhibited the expression of SMA, cTNT, and Tbx5, which are BMP-independent heart mesoderm/early cardiomyocyte genes, but not Brachyury in cultured posterior blastoderm, and combined FGF8b and Nodal, but neither factor alone induced the expression of SMA in association with heart specific markers in cultured epiblast. Although FGF8b did not induce the upregulation of phospho-Smad2, anti-FGF8b properties suppressed phospho-Smad2 in cultured blastoderm. FGF8b was able to reverse the BMP-induced inhibition of cardiomyogenesis. The results suggest that FGF8b acts on the epiblast synergistically with Nodal at the pregastrula stage and may play a role in the expression of SMA during early cardiogenesis.
在原肠胚阶段的心脏发育过程中，骨形态发生蛋白（BMP）活性的抑制会影响心脏的特化，但不会损害平滑肌α-肌动蛋白（SMA）的表达，SMA最初在心脏中胚层表达并被招募到初始心肌原纤维中。囊胚早期后胚层和下胚层之间组织的相互作用对于诱导SMA的表达是必要的，其中Nodal和Chordin被认为参与其中。在这里，我们研究了成纤维细胞生长因子8（FGF8）在SMA表达中的作用。原位杂交和逆转录-聚合酶链反应表明，Fgf8b主要在新生的下胚层中表达。抗FGF8b抗体抑制了SMA、cTNT和Tbx5的表达，这些都是不依赖BMP的心脏中胚层/早期心肌细胞基因，但在培养的后胚盘中不抑制Brachyury，并且FGF8b和Nodal联合使用，但单独任何一种因子都不能在培养的外胚层中与心脏特异性标记物一起诱导SMA的表达。尽管FGF8b没有诱导磷酸化Smad2的上调，但抗FGF8b特性抑制了培养胚盘中的磷酸化Smad2。FGF8b能够逆转BMP诱导的心肌发生抑制。结果表明，FGF8b在原肠胚前期与Nodal协同作用于外胚层，可能在早期心脏发生过程中SMA的表达中发挥作用。
