Hemocytic neoplasia (HN) is a contagious, leukemic-like disease prevalent in several species of marine bivalves. HN is believed to be transmitted via water when neoplastic cells are expelled from infected individuals and absorbed by naïve ones of the same species. As the disease progresses, neoplastic cells proliferate in the hemolymph and replace normal cells throughout the vascular system, ultimately leading to loss of organ function and death of the organism. HN is currently threatening populations of hard clams, Mercenaria mercenaria, primarily in Wellfleet, Massachusetts, USA , resulting in ongoing mortality throughout the warm months of the year. Throughout the summer and fall of 2021, c lams were sampled from this area and were maintained in holding tanks for hemocyte evaluations.
Staining methods used to compa re the morphology of hemocytes to that of neoplastic cells from naïve and HN-infected clams were Protocol, Giemsa, and Periodic Acid-Schiff (PAS). Th e proliferative behavior of neoplastic hemocytes was assessed by immunohistochemical and immunocytochemical detection of PCNA, a cofactor protein of DNA polymerase delta that is essential for replication . A commercial antibody is used in the histological staining of sections to detect PCNA. The expression pattern of this protein in neoplastic cells provides insight into the progression of the disease. A ttempts were made to identify members of the p53 gene family in hard clams and develop primers for reverse transcription qPCR analysis. p53 is an important tumor-suppressing protein which has been linked with HN in other bivalve species. The levels of expression of p53 will be quantified and compared between naïve and infected individuals.
Each of these assessment methods will contribute to a detailed cytological description of neoplastic hemocytes, as well as p53 abundance, in normal and neoplastic hard clams, and will provide information for comparison to other infected bivalve species.