Detection of vitellogenin in a subpopulation of sea urchin coelomocytes.

Sea urchin vitellogenin is a high molecular weight glycoprotein, which is the' precursor of the major yolk protein present in the unfertilized egg. Vitellogenin processing into the major yolk protein and its further enzymatic cleavage during sea urchin embryonic devolopment, has been extensively described, and the adhesive properties of the processed molecnle have been studied. The function of viteUogenin in the adnlt, where it has been found in the coelomic fluid of both male and female individuals, is still unknown, although its role on promoting the adhesion of embryonic cells has been shown. In this report we describe the detection of vitellogenin in Iysates of whole circulating coelomocytes of both male and female sea urchins of the species Paracentrotus lividns. By metrizoic acid gradients we purified total coelomocytes into six subpopulations that were tested for the occurrence of the molecule using vitellogenin-specific polyclonal antibodies. We detected vitellogenin only in the coelomocyte sub population called colorless spherule cells, packed in kidney-shaped granules located around the nucleus. We also showed that coelomocytes respond to stress conditions by discharging vitellogenin into the medium. This result together with previous observations on the adhesive properties of the molecnle suggest a role for vitellogenin in the clotting phenomenon occurring after host invasion.