G protein alpha 12 involved in the heart tube formation via S1P signaling

Ryu-ichi Fukuda1, Kotani Tomoya2, Atsuo Kawahara3, koichi Kawakami4

1)National Institute of Genetics, Shizuoka, Japan, 2)Hokkaido University, Sapporo, Japan, 3)Department of Structural Analysis, National Cardiovascular Center Research Institute, Osaka, Japan, 4)National Institute of Genetics and The Graduate University of Advanced Studies (SOKENDAI), Shizuoka, Japan

 In early heart development, the myocardial precursors migrate between the pharyngeal endoderm and the extra-embryonic yolksyncytial layer (YSL) toward the midline and then fuse to form the functional heart tube. Sphingosine-1-phosphate (S1P) receptor, which is known as miles-apart (mil), is reported to be involved in the signaling pathway of the heart tube formation. Hear we report that G alpha 12 is involved in the S1P signaling and contributes the heart tube formation.
 We have been performing a gene trap screen in zebrafish by using the Tol2 transposon-based gene trap vector containing a splice acceptor and the GFP gene. We obtained fish expressing GFP in temporally and spatially restricted patterns. One of these lines expressed GFP in the heart and carried the transposon integration in the first exon of the gna12 gene, which encodes the G protein alpha 12 subunit. Previously, it has been shown that S1P receptor-G alpha 12/13 signaling was reported to inhibit Rac activation and migration through the coordinated action of G alpha 12/13 in vascular smooth muscle cells. However, it has not been shown which G protein functions downstream of the S1P receptor during the process of the cardiac tube formation. We thought that, if G alpha12 was involved in the S1P signaling pathway and the insertion reduced the activity of G alpha12, it should reduce the activity of S1P signaling. To test this, we injected mil MO into the homozygous fish of this line. Unexpectedly, this line prevented the effect of mil MO and showed normal heart tube formation.
 In these study, we postulate that this line have the constitutive active form of G alpha12 and prevent the effects of mil MO. We hypothesized that G alpha 12 is the important S1P signaling molecule and involved in the cardiac tube formation.