Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) transcript abundance in Y-organs and ecdysteroid titer in hemolymph during a molting cycle of the Blue Crab, Callinectes sapidus

Abstract

Crustacean growth is characterized by molting, whereby the old exoskeleton is shed and replaced by a new and larger version. The cellular events that lead to molting are driven by steroid hormones (ecdysteroids) secreted by paired endocrine glands (Y-organs). Between molts, ecdysteroid production is suppressed by a polypeptide molt-inhibiting hormone (MIH) released from neurosecretory cells in the eyestalks. Although a decrease in the MIH titer precedes the upsurge in ecdysteroidogenesis, it is hypothesized that a positive regulatory signal is also required for full activation of Y-organs. Existing data point to an intracellular Ca2+ signal. Ca2+ signaling is dependent on a tightly regulated Ca2+ gradient, achieved through membrane transport proteins. One such protein, the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), pumps Ca2+ from cytosol to the lumen of the ER. We have recently cloned from Y-organs of the blue crab (Callinectes sapidus) a cDNA encoding a putative Cas-SERCA protein. In studies reported here, quantitative PCR (QPCR) was used to quantify Cas-SERCA transcript abundance in Y-organs during a molting cycle, and radioimmunoassay was used to quantify ecdysteroids in hemolymph. The abundance of the Cas-SERCA transcript in Y-organs increased gradually during pre-molt. Similarly, the level of ecdysteroids in hemolymph increased during pre-molt. The results are consistent with the hypothesis that Cas-SERCA functions to maintain Ca2+ homeostasis in Y-organs. Cas-SERCA transcript abundance also changed in several non-ecdysteroidogenic tissues during a molting cycle. The pattern of change differed among tissues suggesting a functional role for SERCA in each.