On the possible role of endogenous lectins in early animal development

In this review I have tried to summarize the information available on the lectins of developing embryos. The emerging evidence indicates that during fertilization carbohydrate-binding proteins play a role in sperm adhesion and in the reorganization of the extracellular matrix of the fertilized egg. Results also indicate that in adult tissues lectins participate in cell recognition and adhesion, and that several galactose-binding lectins function as receptors for laminin and, in principle could also interact with polylactosamine groups of other extracellular matrix glycoproteins. Since in developing embryos lectins are located at the cell surface, and colocalize with extracellular matrix glycoproteins, they could play a role in transitory adhesive interactions and in the segregation of organ primordia. On the basis of experiments in cultured cell lines, it has been suggested that lectins are involved in lysosomal and nuclear glycoprotein transport. These carbohydrate-binding proteins could also regulate development by modulating these processes in the embryo. Since galactose-binding lectins are mitogenic, and are present in high concentration in the chick yolk sac, these proteins could be released into the embryonic circulation, bind to cells expressing appropriate receptors, and act as growth regulators, by modulating cell division of specific cell lineages.