Meeting Abstract
59.2 Wednesday, Jan. 6 Regulation of Methyl Farnesoate Esterase during development of the tadpole shrimp, Triops longicaudatus GLEDHILL, Michael R*; TRAN, Michael C; TSUKIMURA, Brian; California State Univ., Fresno mrgledhi@csufresno.edu
Methyl farnesoate (MF), a putative crustacean hormone, is well documented as the precursor to juvenile hormone in insects. In crustaceans, MF promotes juvenile morphology, with low MF levels being necessary for development (Laufer and Biggers, 2001). In juvenile tadpole shrimp, Triops longicaudatus, MF decreased ovary weight and oocyte number when incorporated into food pellets (Tsukimura et al., 2006). MF is metabolized by the enzyme methyl farnesoate esterase (MFE). The purpose of this experiment was to determine the base rate of MFE at days 4, 8, 12, and during oocyte development, plus determine if tadpole shrimp in response to dietary MF (6 µg/g), modulate their MFE rates. Enzymatic rates were determined by incubation of tadpole shrimp tissue with the radio-labeled substrate, 3H-MF. The polar products of the digestion were separated from the remaining non-polar MF by hexane, acetonitrile, and saline water (Laufer et al., 1987). There was an overall decline in the rate of MFE with age. Sexually immature animals, characterized by a lack of cysts in brood sacs, had an average MFE rate of 23.2 ± 3.2 (pmol MF/mg protein/min) compared with sexually mature animals with a MFE rate of 12.1 ± 1.4. The transition appeared to be rapid and around the first expansion of vitellogenesis. When given dietary MF, animals appeared to respond by decreasing their MFE rate as juveniles (Control: 25.3 ± 3.5, MF-treated: 16.1 ± 3.9) and as adults (15.6 ± 1.5 vs. 7.3 ± 2.0). These data support the hypothesis that MF must be cleared from the organism before it can develop into a sexually mature animal. However, the decline in MFE rate observed in animals receiving exogenous MF could potentially be due to toxic level doses of MF.
