TRANSCRIPTIONAL REGULATION OF TUBULIN GENE-EXPRESSION IN DIFFERENTIATING TROCHOBLASTS DURING EARLY DEVELOPMENT OF PATELLA-VULGATA

The expression of alpha- and beta-tubulin genes during the early devel opment of the marine mollusk Patella vulgata has been investigated. Fr om the 32-cell stage onwards, an enhanced expression of both alpha- an d beta-tubulin mRNAs was detected in the primary trochoblasts. After o ne additional cleavage, these cells become cleavage-arrested and then form cilia. They are the first cells to differentiate during Patella d evelopment. Later, alpha- and beta-tubulin mRNA is also found in the a ccessory and secondary trochoblasts. Together these three cell-lines f orm the prototroch, the ciliated locomotory organ of the trochophore l arva. The early and abundant expression of tubulin genes precede and a ccompany cilia formation in the trochoblasts and provides us with an e xcellent molecular differentiation marker for these cells. Apart from the trochoblasts, tubulin gene expression was also found in other cell s at some stages. At the 88-cell stage, elevated tubulin mRNA levels w ere found around the large nucleus of the mesodermal stem cell 4d. In later stages, tubulin gene expression was detected in the cells that f orm the flagella of the apical tuft and in the refractive bodies. An a lpha-tubulin gene was isolated and characterized. A lacZ fusion gene u nder control of the 5' upstream region of this tubulin gene was microi njected into embryos at the two-cell stage. The reporter gene product was only detected in the three trochoblast cell-lines at the same time as tubulin genes were expressed in these cells. Reporter gene product was not detected in any other cells. Thus, this 5' upstream region of this alpha-tubulin gene contains an the elements required for the cor rect spatiotemporal pattern of expression.