Moshel-Lynch, S.*; Collier, J.: Conservation of Mesodermal-specific Genes in Molluscs

While bilateral symmetry is the ancestral state of molluscs, the gastropods have adopted various developmental pathways leading from bilateral symmetry to complex asymmetrical body plans. Because many of the asymmetrical organ systems are mesodermal derivatives the identification of mesodermal regulatory genes is essential for understanding how the molluscs diversified. It has been well demonstrated that twist and snail play a significant role in both determination and differentiation of mesoderm in a variety of organisms. Thus, using the polymerase chain reaction we have identified these two genes in the genomes of various molluscs. By in situ hybridization and immunocytochemistry we have detected the expression of twist and snail in mesodermal lineages of the marine mud snail Ilyanassa obsoleta. We have also found that both of these genes are maternally expressed. Throughout the animal kingdom there are a variety of different mechanisms for mesoderm formation, and our study of teloblastic mesoderm formation in a spiralian embryo extends the body of evidence for the conservation of genes used for mesoderm formation. This body of evidence illustrates genomic antiquity in the face of developmental diversifiction.