The Effect of Gene Knockout on Heat Shock-Induced Polyploidization in Loach ().

(1) Background: Polyploid fish are highly important in increasing fish production, improving fish quality, and breeding new varieties. The loach (), as a naturally polyploid fish, serves as an ideal biological model for investigating the mechanisms of chromosome doubling; (2) Methods: In this study, tetraploidization in diploid loach was induced by heat shock treatment, and, for the first time, the role of the key cell cycle gene (cyclin-dependent kinase 1) in chromosome doubling was investigated; (3) Results: The experimental results show that when eggs are fertilized for 20 min and then subjected to a 4 min heat shock treatment at 39-40 °C, this represents the optimal induction condition, resulting in a tetraploid rate of 44%. Meanwhile, the results of the knockout model (2n ) constructed using CRISPR/Cas9 showed that the absence of significantly increased the chromosome doubling efficiency of the loach. The qPCR analysis revealed that knockout of significantly upregulated cyclin genes (, and ), while inhibiting expression of the separase gene ( < 0.05); (4) Conclusions: During chromosome doubling in diploid loaches induced by heat shock, knocking out the gene can increase the tetraploid induction rate. This effect may occur through downregulation of the gene. This study offers novel insights into optimizing the induced breeding technology of polyploid fish and deciphering its molecular mechanism, while highlighting the potential application of integrating gene editing with physical induction.