Biochemical characterization and physiological role of cortical rods in black tiger shrimp, Penaeus monodon

Cortical rods (CRs), precursors of egg jelly investment in many penaeoid shrimp, are composed of different proportions of proteins and carbohydrates, the physiological role of which still requires extensive investigation. In this study, we demonstrated the biochemical properties of the CRs and their role in the induction of the acrosome reaction (AR). Profiles of the isolated CRs revealed a number of major protein bands ranging from 35 to 230 kDa. These CR proteins were extensively glycosylated and sulfated. Lectin-based carbohydrate analysis further revealed the highest reactivity of concanavalin A (Con A) among other lectins used. In addition, the selective interference of Con A binding with mannose but not glucose indicated that CR glycoproteins were of high-mannose type. Using immunoblotting with anti-CR antibody, we further demonstrated that part of egg water (EW, a natural AR inducer) was derived from miscible components of the CRs. Physiological tests of water-soluble CR (wsCR) revealed its high AR inducing competency comparable to that of EW, which was far superior to that of acid-urea treated CR (auCR). Furthermore, the wsCR-induced AR was selectively inhibited by Con A, suggesting the significance of the exposing mannose residues in regulating P. monodon sperm AR response.