Flow cytometric and chromosome analysis of softshell clams, Mya arenaria, with disseminated neoplasia

Abstract

Studies were carried out to determine the DNA content and genomic characteristics of abnormal cells in the hemolymph of the softshell clam, Mya arenaria , affected with disseminated neoplasia (DN). Normal clam cells had a model chromosome number of 34 with a range of 26–39, whereas DN cells had chromosome numbers ranging from 44 to 80 with a mode of 69. Chromosome spreads of hemolymph cells from DN clams contained acrocentric and telocentric chromosomes which were absent from normal cells. By flow cytometric analysis, the quantity of DNA in normal clam hemocytes was 3.2 pg cell −1 based on comparisons to human lymphocyte and trout erythrocyte standards. The circulating cells of all clams with DN intensities greater than 10% examined by flow cytometry showed distinct DNA aneuploidy. Normal cells were assigned a DNA index (DI) of 1.0; the DN cells had a mean DI of 1.76 with a range from 1.25 to 2.05. There was no evidence of a pentaploid population as seen in the mussel, Mytilus edulis , affected with DN. A significantly higher proportion of the DNA aneuploid cells were in the S phase of the cell cycle than normal cells. Aneuploid cells in G O /G 1 were also larger in size than their diploid counterparts. Both the flow cytometry and the chromosome analysis indicate that there is a quantitative difference in the DNA content of DN cells compared to normal cells.