Identifying key drivers of tentacle specialization in Cipangopaludina chinensis through transcriptomic analysis

The modification of the male right tentacle (MRT) into a copulatory organ in Cipangopaludina chinensis represents a prominent sexual dimorphism, yet the molecular mechanisms underlying its development remain poorly understood. This study observed the distinctive histological morphology of MRT, and then explored its potential genetic regulatory networks through transcriptomic analysis. Comparative transcriptome analysis across tentacles of different sexes and sides identified numerous differentially expressed genes (DEGs). Notably, the homeobox gene Pitx2, a central regulator of left-right asymmetric development in animals, was significantly upregulated in the MRT. Transcription factors involved in sexual development (e.g., Dmrta2, Sox10), genes related to hormone synthesis (Daf9, Cyp2j4), and the pro-apoptotic gene Bax were also specifically upregulated, while the apoptosis inhibitor gene Iap1 was downregulated. Weighted Gene Co-expression Network Analysis (WGCNA) further identified key modules highly correlated with the MRT phenotype, which were enriched for biological processes such as hormone response, cell morphogenesis, and apoptosis-related pathways. Our results suggest that the sexually dimorphic development of the tentacle in C. chinensis likely involves the coordinated action of a Pitx2-mediated left-right asymmetry pathway, sex-determination signals, and a local hormone-induced apoptotic remodeling program, revealing a complex regulatory mechanism underlying its morphological specialization.