HOLFORD, K.C.*; BORST, D.W.: The effects of sinus gland extracts on transcript levels of farnesoic acid O-methyl transferase (MeT) in the lobster mandibular organ.

Methyl farnesoate (MF) appears to have important roles in the regulation of crustacean reproduction, molting, and behavior. In decapod crustaceans, the mandibular organ (MO) is the principle site of MF synthesis and is inhibited by a peptide from the sinus gland (SG, a neuroendocrine tissue in the eyestalk). This MO-inhibiting hormone (MO-IH) lowers MF synthesis in part by reducing the activity of MeT (the final enzymatic step in MF production). We investigated the mechanisms of this inhibition by treating eyestalk-ablated lobsters (Homarus americanus) with a SG extract (0.2 SG equivalents) in saline-0.1% BSA or with saline-BSA alone (control). Hemolymph samples were taken for MF analysis before and 3 hours after treatment. MO’s were then removed and used to determine MeT activity and MeT transcript levels. SG treatment caused a 68% decrease in hemolymph levels of MF. Control animals showed no change in MF levels. Likewise, MeT activity of MOs from SG treated animals was 85% less (P < 0.001) than that measured in MOs from control animals. However, MeT transcript levels in these two groups were not significantly different (P > 0.11). These data indicate that the decrease in MeT activity caused by MO-IH is not mediated by a decrease in MeT gene expression. Rather, SG extract appears to act either by inhibiting the translation of MeT mRNA or through the post-translational modification of MeT. (Supported by NIH-AREA grant 1-R15 HD37953-01 to DWB).