Insulin‐Like Growth Factor 1 ( <i>IGF1</i> ) in the Chinese Soft‐Shelled Turtle, <i>Pelodiscus sinensis</i> : Molecular Characterization, Expression Pattern, and Polymorphism Analysis

Insulin‐like growth Factor 1 ( IGF1 ) plays a vital role in vertebrate growth, and its sexually biased expression may influence the development and evolution of sexual size dimorphism (SSD). To investigate the role of IGF1 in regulating the growth of the Chinese soft‐shelled turtle ( Pelodiscus sinensis ), this study quantified IGF1 mRNA abundance across various tissues, phenotypes, and steroid hormone treatments using quantitative real‐time polymerase chain reaction (qRT‐PCR). Additionally, the polymorphism of the IGF1 gene was analyzed and genotyped using the tetra‐primer amplification refractory mutation system PCR (ARMS‐PCR). The findings revealed that the full‐length cDNA sequence of the IGF1 gene ( PsIGF1 ) in P. sinensis was 1790 bp, with the liver identified as the primary site of PsIGF1 expression. The expression of PsIGF1 was positively correlated with rapid growth and followed a pattern indicative of its involvement in sexually dimorphic growth. Treatment with 17α‐methyltestosterone (MT) significantly increased hepatic IGF1 gene expression, while 17β‐estradiol ( E 2 ) showed the opposite effect, suggesting that IGF1 may be a critical factor underlying SSD in P. sinensis . Furthermore, a single‐nucleotide polymorphism (SNP) identified in the 5′ untranslated region (UTR) of PsIGF1 was significantly associated with growth traits in P. sinensis ( p value &lt; 0.05). These results provide a foundation for further research into the regulatory mechanisms of IGF1 in the development and SSD of P. sinensis .