Projects

The crustacean molt-inhibiting hormone receptor and induction of molting in blue crabs (Callinectes spadius)

End Date: 02/1/10

Abstract

The soft crab industry is limited by a supply of premolt blue crabs (Callinectes sapidus) that is both seasonal and unpredictable.  Steroid hormones termed ecdysteroids control cycles of growth and molting in crustaceans.  Ecdysteroids are synthesized by paired endocrine glands, the Y-organs.  The production of ecdysteroids by Y-organs is suppressed by molt-inhibiting hormone (MIH), a polypeptide neurohormone produced in eyestalk neural ganglia. Thus, it is hypothesized that MIH inhibits Y-organs during much of the molt cycle, and that a molting sequence is initiated when MIH secretion diminishes or stops. It follows that blocking the suppressive action of MIH will induce molting. MIH suppresses ecdysteroid production by binding to a cell surface receptor on Y-organs. We have recently cloned from blue crab Y-organs a putative MIH receptor (a receptor guanylyl cyclase, CsGC-YO1), and have developed a candidate receptor blocker (antipeptide antibodies raised against the extracellular domain, anti-CsGC-YO1). The specific objectives of the proposed research are to determine (1) whether the cloned receptor is an authentic MIH receptor, and (2) whether the candidate receptor blocker is effective in inducing molting in blue crabs. Identification and characterization of the MIH receptor would constitute a significant contribution to the field of invertebrate endocrinology. Controlled induction of molting could provide an abundant and predictable supply of soft-shelled crabs, a benefit to the soft crab industry and to consumers of seafood.  At the end of the requested two-year funding period, we anticipate that the general approach will have been validated and that we will be well positioned to pursue practical delivery systems (e.g., by way of a prepared diet) for the blocker. 

Objectives

A major gap in knowledge of the regulation of crustacean growth and molting is lack of information on the molt-inhibiting hormone (MIH) receptor. We have recently cloned from blue crab (Callinectes sapidus) molting glands a putative MIH receptor (CsGC-YO1), and have developed a candidate receptor blocker (anti-CsGC-YO1). 
Year 1

  1. to determine whether the cloned receptor is an authentic MIH receptor.   

Year 2

  1. to determine whether the candidate receptor blocker is effective in inducing molting in blue crabs.

Methodology

Year 1
To determine whether the cloned receptor is an authentic MIH receptor, we will (a) express the receptor in mammalian (COS-7) cells, and (b) test the ability of recombinant MIH to bind and activate the expressed receptor. 
Year 2
To test the effectiveness of the receptor blocker, we will inject the blocker into blue crabs and then (a) monitor the level of ecydsteroids in hemolymph, and (b) score morphological indicants of the molt stage and the time to molting. Once an effect has been established in vivo, titration experiments will be conducted to determine the lowest effective dose. 

Rationale

Year 1
Despite the central role of MIH in regulation of growth and postembryonic development in this economically and ecologically important group of organisms, the MIH receptor has not been isolated or thoroughly characterized for any crustacean species. Identification and characterization of the MIH receptor would constitute a significant contribution to the field of invertebrate endocrinology, and would lead (in year 2) to experiments designed to permit the induction of molting in blue crabs, a benefit to the soft crab industry and to consumers of seafood.  
Year 2
The soft crab industry is limited by a supply of premolt blue crabs (Callinectes sapidus) that is both seasonal and unpredictable.  Controlled induction of molting could provide an abundant and predictable supply of soft-shelled crabs, a benefit to the soft crab industry and to consumers of seafood.

For More Information Contact: the MASGC Research Coordinator, Loretta Leist (Loretta.leist@usm.edu). 
Please reference the project number R/SP-19.