Molecular Characterization and Functional Analyses of IGFALS in the Chinese Soft-Shelled Turtle ( <i>Pelodiscus sinensis</i> )

The insulin-like growth factor (IGF) system plays a crucial role in the regulation of development, reproduction, and growth. Within this system, the IGF acid-labile subunit ( IGFALS ) plays a pivotal role in modulating IGF activity by stabilizing circulating IGF complexes. In this study, two IGFALS gene transcripts, named IGFALSX1 and IGFALSX2 , were identified for the first time in the Chinese soft-shelled turtle ( Pelodiscus sinensis ). The cDNA sequences of IGFALSX1 and IGFALSX2 were 2,452 bp and 2,520 bp, respectively, encoding 617 and 616 amino acids (AAs). The IGFALS gene was expressed in all tissues of P. sinensis , with particularly high expression in the liver, gonads, and lungs, and marked sexual dimorphism observed in the liver. Short-term stimulation of juvenile P. sinensis with sex steroids led to significant changes in IGFALS expression in the livers of both male and female individuals, suggesting its potential involvement in steroid-mediated growth modulation. These observations collectively indicate that IGFALS may function as a key molecular mediator in the steroid-responsive growth regulatory pathway of P. sinensis .