ABSTRACT
Objective To investigate the functional role of a soluble secretion factor midkine-a in the process of zebrafish embryonic heart development .Methods Whole-mount in situ hybridization was performed to detect whether midkine-a is expressed in the embryonic heart .In the transgenic embryonic heart of Tg ( pmidkine-a:EGFP) , the expres-sion of EGFP in the heart was monitored .Multiple heat shock treatments were applied to Tg (phsp:midkine-a:EGFP) em-bryos in order to overexpress midkine-a, and the phenotype of the heart was observed .The heterozygous Tg ( phsp:mid-kine-a:EGFP) fish were crossed with homozygous Tg (pcmlc2:dsRed) fish, which specifically expresses RFP in the nucle-oli of embryonic cardiomyocytes to facilitate myocyte number counting .To get Tg ( phsp:midkine-a:EGFP/pcmlc2:dsRed)embryos, and the total number of cardiomyocytes in their heart was counted and compared with the controls when the heat shock induced overexpression of midkine-a.Morphonino knocked out of midkine-a was performed to observe the heart phe-notype.Results Midkine-a was expressed in the zebrafish embryonic heart during development .Overexpression of mid-kine-a led to a smaller heart and reduced total number of cardiomyoctes in a single heart , which might be associated with the smaller heart phenotype .Morphonilo knocked out of midkine-a had no effect upon the heart development .Conclusions Midkine-a impedes zebrafish embryonic heart growth by limiting its cardiomyocyte pool .