Specific binding of lectins with the nucleus of the sea urchin embryo and changes in the lectin affinity of the embryonic chromatin during the course of development.

(1) Embryonic cells of sea urchins were made permeable by treating them with glycerol solution for the purpose of allowing penetration of macromolecules into the cell. With the use of such permeabilized cells, several kinds of fluorescent dye-labeled lectins were introduced into the cell, and it was found that some lectins showed notable affinity with the nucleus as compared with cytoplasmic structures. (2) Isolated chromatin was incubated with several kinds of fluorescent dye-labeled lectins in vitro, and the amount of lectins bound with the chromatin was measured by fluorometry. By means of this method, the lectin-binding capacity of chromatin was estimated and compared at various stages of development. It was found that lectins could be classified into three groups according to the mode of binding with the chromatin: (a) Extent of binding increased notably at the gastrula stage (Con A and RCA-120); (b) extent of binding showed a temporary decrease at the gastrula stage (TTA); and (c) very low level of binding was maintained throughout all stages, and no particular change was observed at any stage of development (WGA, SBA, and UEA-I). (3) These facts seem to suggest that lectin-binding components are contained in sea urchin chromatin, and that drastic changes occur in these components of chromatin at the stage of gastrulation. It was proposed that the lectin-binding components such as proteoglycans and glycoproteins may play regulatory roles in embryonic chromatin at early stages of development.