Disseminated neoplasia (DN), a transmissible cancer affecting bivalves, poses a significant threat to both wild and aquaculture populations of hard clam (Mercenaria mercenaria), particularly along the U.S. Atlantic coast. To investigate the molecular mechanisms underlying DN, we conducted single-cell RNA sequencing (scRNA-seq) of hemocytes from neoplastic and healthy clams. Cohabitation experiments exposing healthy clams to neoplastic clams confirmed successful transmission of the disease. Hemocytes were then collected from healthy, neoplastic and exposed individuals and processed using the 10x Genomics Chromium platform.
Clustering of hemocytes revealed nine distinct populations, with Cluster 3 predominantly composed of cells from neoplastic samples (Fig. 1). KEGG enrichment analysis showed that this cluster exhibited downregulation of pathways related to phagosome formation, endocytosis, ubiquitin-mediated proteolysis, and FoxO signaling (Fig. 2), suggesting potential mechanisms of immune evasion and resistance to apoptosis. Weighted gene co-expression network analysis identified six gene modules within Cluster 3. Of these, three modules were highly expressed in neoplastic cells and appear to play roles in metabolic reprogramming and the activation of growth and survival pathways. These modules were enriched for genes involved in DNA replication, WNT, TGF-β, and Notch signaling, as well as other metabolism-related functions.
Together, these findings suggest that neoplastic cells in hard clams undergo significant molecular changes that support uncontrolled growth and survival. This study provides new insights into the mechanisms of disseminated neoplasia and identifies potential molecular targets for future research and disease management in aquaculture