Progressive development of circulating polyploid cells in Mytilus with hemic neoplasia

The progressive development of hemic neoplasia in Mytilus is described using a flow cytometric method. Two experiments were conducted in order to determine the DNA content and evolution of the disease in individual Mytilus. In disease free individuals, either 1 or 2 populations of circulating cells (G,, and GLd were detected on the basis of relative DNA content, containing multiples of 2.00 to 2.21 haploid (n) DNA content. In mussels with progressive hemic neoplasia, an increase in an apparently polyploid population (measured 5.1 n) occurred in conjunction with a decrease in the proportion of G1, cells. Subsequent to the increase of the 5 . l n population, the formation of a second apparently polyploid population of circulating cells with a mean measured DNA content of 10.ln occurred and increased over time. The presence of these cell populations with these two ploidy levels represented a single population of autonomously replicating polyploid hemocytes in circulation. These polyploid circulating cell popu1,itions correspond 10 morphological changes in circulating cells which are described from hemocytological preparations. In addition, a second, rarer form of the disease. characterized by an Increase of tetraploid neoplastic cells in circulation was observed. The 2 forms of the disease may represent alternative chromosomal lesions resulting from 2 alternative modes of integration of a foreign genome into the host genome. The significance of these findings on the observation of progression of the disease and on hypothetical etiologies is discussed.