Developmental regulation of lectin-binding patterns in Paracentrotus lividus gonads, gametes, and early embryos

By use of several lectins (ConA, WGA, SBA, GS I, PNA), a study was carried on gametes and developing embryos of the sea urchin Paracentrotus lividus, to investigate developmental changes in cell surface, leading to changements in cell-environment interactions. ConA, WGA, and SBA, with high affinity, bind to the vitelline membrane of unfertilized eggs, while PNA labelling at the same site is weak; GS I-binding is only present in the cytoplasm and cortical region of the unfertilized eggs. Immediately after fertilization, no ConA-binding is present in the membrane, while WGA- and SBA-binding molecules are located in the fertilization layer. In zygotes, 40 min after fertilization, ConA affinity sites were again present in both cytoplasm and cortical region. During cleavages and gastrulation, ConA binds to the blastomere cytoplasm and cortical region, to the intercellular matrix, and to the cytoplasm of mesenchyme cells. WGA binds to the cortical region of cleaving blastomeres, including the hyaline layer, up to the unhatched blastula. Then it labels the gastrula inner and outer surfaces. SBA binds to the blastomere membranes; no GS I- and PNA-binding was detected during embryonic development. Sperms are bound by all the lectins, except GS I. Mannose and glucose conjugates are the most represented throughout the whole development of P. lividus, and their origin and locations are developmentally regulated. Galacto-residues are scarcely represented or are masked by other terminal sugars (e.g. sialic acid), and become functional during particular developmental events (cell movements).