Microinjection of lectins, hyaluronidase, and hyaluronate fragments interferes with cleavage delay and mesoderm induction in embryos of Patella vulgata.

In embryos of Patella vulgata at the 32-cell stage, one of the four vegetally located macromeres makes contacts with overlying animal micromeres. As a result, this macromere (designated 3D) divides significantly later than the other macromeres and forms the mesodermal stem cell 4d. Shortly before and during this interaction two types of extracellular matrix are present: a basal lamina-like layer on the tips of the micromeres and a loose fibrillar meshwork in the blastocoel. In this paper we examine the role of the matrix in cleavage delay and mesoderm determination. The microinjection of extracellular matrix-binding lectins, or of hyaluronidase, or of decasaccharide fragments of hyaluronate into the blastocoel results in embryos in which either no or two macromeres are delayed in cleavage and are presumably determined as mesodermal stem cells. We suggest that the fibrillar meshwork is needed for macromere elongation toward the micromeres and that the basal lamina-like layer is involved in the determination process itself.