Characterization of Midkine in tongue sole (Cynoglossus semilaevis)and its role on the germ layer genesis in zebrafish (Danio rerio)

Midkine (Mdk) is a cytokine involved in controlling tissue repair and new tissue development, and regulating inflammation involved in several signaling pathway, such as the mitogen-activated protein kinase (MAPK) and phosphatidyl inositol 3-kinase (PI3K)/AKT pathways. But the role of Mdk in the development of Cynoglossus semilaevis is poorly understood. In this study, the Midkine of C. semilaevis (CsMdk) was cloned, and its spatiotemporal expression pattern and structural characteristics were analyzed. Furthermore, the essential genes related to nervous system development and germ layer formation marker gene were identified by qRT-PCR and in situ hybridization after overexpression the CsMdk via zebrafish model. The result showed CsMdk was mainly expressed in the brain of embryo, especially in the diencephalon, mid-hindbrain boundary (MHB) and hindbrain. In adult fish, it could only be detected in brain. Overexpression of CsMdk mRNA in zebrafish embryos suppressed the development of forebrain, midbrain, hindbrain and the notochord in zebrafish and influence the development of the mesoderm. All results showed CsMdk played a significant role on the germ layer and nervous development.