Proteomic Analysis of the Crustacean Molting Gland (Y-Organ) Over the Course of the Molt Cycle

Molting in crustaceans is a highly complex physiological process involving negative regulation by two paired endocrine glands, the X-organ/sinus gland complex (XO/SG) and the Y-organ (YO). The XO/SG complex is responsible for making molt-inhibiting hormone (MIH) which negatively regulates synthesis of the molting hormones, ecdysteroids, by the YO. Analysis of gene expression in the XOs and YOs has led to the development of a proposed molecular signaling pathway which regulates ecdysteroidogenesis and subsequent molting in crustaceans. In this study, changes in protein abundance in the YO were characterized over the course of a molt cycle (intermolt, early premolt, mid premolt, and late premolt) induced by multiple leg autotomy (MLA) in the blackback land crab, Gecarcinus lateralis. In all, 457 distinct protein spots were detected in the molting gland using two-dimensional gel electrophoresis, of which 230 (50%) changed significantly in abundance over the course of the molt cycle (one-way permutation ANOVA, p≤0.05). Changes in protein abundance were most notable between the intermolt and the three premolt stages, indicative of a biological ‘on-off’ switch in the Y-organ. Several hemolymph species proteins, including hemocyanin, cryptocyanin, and transglutaminase, were identified which characterized physiological changes associated with molting beyond the Y-organ. An abundance of cytoskeletal proteins were identified which correspond with glandular hypertrophy and are indicative of vesicular-mediated exocytosis, possibly of ecdysteroids. Further, several proteins involved in the immune, proteostasis, and oxidative stress response are characteristic of supporting the dynamic and demanding cellular changes associated with ecdysteroidogenesis and the transition of the Y-organ from the basal to the highly active state. Many proteins involved in energetic pathways including glycolysis, the citric acid cycle, amino acid metabolism, and one-carbon metabolism changed in abundance in response to both the higher energy demands and the requirement for precursors of macromolecular synthesis of the YO over the molt cycle. Taken together, these changes in diverse physiological pathways represent the complexity involved with regulation of the Y-organ, even with just the single proposed physiological purpose of ecdysteroidogenesis