Functional Study of PTSMAD4 in the Spermatogenesis of the Swimming Crab Portunus trituberculatus

<i>Portunus trituberculatus</i> holds significant economic value. The spermatogenesis is regulated by numerous signaling pathways. Among them, the TGF-β signaling pathway plays an important role in the development of testes and spermatogenesis. Smad4 is a Co-Smad protein that forms a complex with R-Smad to regulate the expression of target genes. The sperm structure in crustaceans differs greatly from that in mammals, with mature sperm lacking tails. Our previous studies have reported the function of R-Smad in the spermatogenesis of <i>P. trituberculatus</i>. In this study, we cloned the full-length cDNA sequence of <i>PTSMAD4</i>; immunofluorescence technology revealed that PTSMAD4 is expressed throughout all stages of spermatogenesis. We knocked down the expression of PTSMAD4 in <i>P. trituberculatus</i> using RNAi technology, and the immunofluorescence results show abnormal co-localization and weakened signals of PTSMAD4 and PTSMAD2. Additionally, transcriptome sequencing results enriched functional genes and pathways related to spermatogenesis. This study indicates that PTSMAD4 may participate in the spermatogenesis process through its involvement in signal transduction. This research not only lays the foundation for further study of the function of the TGF-β signaling pathway in spermatogenesis but also provides a theoretical basis for further investigation of the spermatogenesis mechanism in crustaceans.