Research article

Glycogen synthase kinase 3α and 3β have distinct functions during cardiogenesis of zebrafish embryo

Huang-Chieh Lee¹ , Jen-Ning Tsai² , Pei-Yin Liao¹ , Wei-Yuan Tsai¹ , Kai-Yen Lin¹ , Chung-Cheng Chuang³ , Chi-Kuang Sun³ , Wen-Chang Chang^4,5 and Huai-Jen Tsai¹

¹  Institute of Molecular and Cellular Biology, National Taiwan University, NO. 1, Roosevelt Road, Sec. 4, Taipei 106, Taiwan

²  School of Medical Laboratory and Biotechnology, Chung Shan Medical University, Taichung 402, Taiwan

³  Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University and Research Center for Applied Sciences, Academia Sinica, Taipei 10617, Taiwan

⁴  Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan

⁵  Institute of Biological Chemistry, Academia Sinica, Nankang 115, Taiwan

author email corresponding author email

BMC Developmental Biology 2007, 7:93doi:10.1186/1471-213X-7-93

Published:	3 August 2007

Abstract

Background

Glycogen synthase kinase 3 (GSK3) encodes a serine/threonine protein kinase, is known to play roles in many biological processes. Two closely related GSK3 isoforms encoded by distinct genes: GSK3α (51 kDa) and GSK3β (47 kDa). In previously studies, most GSK3 inhibitors are not only inhibiting GSK3, but are also affecting many other kinases. In addition, because of highly similarity in amino acid sequence between GSK3α and GSK3β, making it difficult to identify an inhibitor that can be selective against GSK3α or GSK3β. Thus, it is relatively difficult to address the functions of GSK3 isoforms during embryogenesis. At this study, we attempt to specifically inhibit either GSK3α or GSK3β and uncover the isoform-specific roles that GSK3 plays during cardiogenesis.

Results

We blocked gsk3α and gsk3β translations by injection of morpholino antisense oligonucleotides (MO). Both gsk3α- and gsk3β-MO-injected embryos displayed similar morphological defects, with a thin, string-like shaped heart and pericardial edema at 72 hours post-fertilization. However, when detailed analysis of the gsk3α- and gsk3β-MO-induced heart defects, we found that the reduced number of cardiomyocytes in gsk3α morphants during the heart-ring stage was due to apoptosis. On the contrary, gsk3β morphants did not exhibit significant apoptosis in the cardiomyocytes, and the heart developed normally during the heart-ring stage. Later, however, the heart positioning was severely disrupted in gsk3β morphants. bmp4 expression in gsk3β morphants was up-regulated and disrupted the asymmetry pattern in the heart. The cardiac valve defects in gsk3β morphants were similar to those observed in axin1 and apc^mcr mutants, suggesting that GSK3β might play a role in cardiac valve development through the Wnt/β-catenin pathway. Finally, the phenotypes of gsk3α mutant embryos cannot be rescued by gsk3β mRNA, and vice versa, demonstrating that GSK3α and GSK3β are not functionally redundant.

Conclusion

We conclude that (1) GSK3α, but not GSK3β, is necessary in cardiomyocyte survival; (2) the GSK3β plays important roles in modulating the left-right asymmetry and affecting heart positioning; and (3) GSK3α and GSK3β play distinct roles during zebrafish cardiogenesis.