Juvenile hormone metabolism in the plasma, integument, midgut, fat body, and brain during the last instar of the tobacco hornworm, Manduca sexta (L.)

Abstract

Juvenile hormone (JH) Ill esterase and JH I l l epoxide hydrolase activity was found in the integument, midgut, fat body, and brain during last instar development of the tobacco hornworm, Manduca sexta. JH esterase activity was primarily located in the cytosol in these tissues while the majority of the JH epoxide hydrolase activity was found in the microsomes. A prewandering (on day 3) and postwandering (on day 8) peak in plasma JH Ill esterase activity occurs in the last instar of gate I M. sexta. The JH esterase activity profile in integument, midgut, fat body, and brain followed a similar pattern to that of the plasma. The only exception to this was the absence of the postwandering, prepupal (on day 8) JH esterase peak in the fat body. The topical application of the juvenoid, (RS)-methoprene, failed to induce fat body JH esterase activity but increased activity in the plasma, integument, midgut, and brain in M. sexta prepupae. These results indicate that the source of plasma JH esterase activity is not always the fat body as previously hypothesized. The developmental profile of tissue JH epoxide hydrolase activity was also similar to that of J H esterase suggesting that both enzymes may be regulated partly by the same factors and that JH epoxide hydrolase may also have an important, previously unrecognized functional role in JH regulation and insect metamorphosis. Multiple isoelectric forms of tissue-specific JH esterases and JH epoxide hydrolases were found in integument, midgut, fat body, and brain. The JH esterases in these tissues had isoelectric points more acidic than that for plasma. Tissue a-naphthyl acetate esterase, developmental profiles, and inhibitor sensitivity to 3-(octylthio)-l , I ,l-trifluoropropan-2-one differed sig-

Tissue and stage-specific juvenile hormone esterase (JHE) and epoxide hydrolase (JHEH) enzyme activities and Jhe transcript abundance in lines of the cricket Gryllus assimilis artificially selected for plasma JHE activity: Implications for JHE microevolution

“…The non-parallel developmental profiles of plasma, midgut, and fat body JHE activities, during specific periods of the last juvenile stadium of G. assimilis also suggest that JH degradation may differ among various organs, genetic stocks, and stages of development in G. assimilis as has been proposed for a number of lepidopterans (Hammock, 1985;Jesudason et al, 1992). Degradation of JH by JHE in tissues other than hemolymph has not been well studied in insects but is likely to be an important component of JH titer regulation, especially when the JH titer within specific tissues must differ from that of the hemolymph.…”

“…In contrast to the single JHE plasma activity peak during development in hemimetabolous insects such as G. assimilis, holometabolous insects have two plasma JHE activity peaks. In T. ni, JHE activity changed largely in concert in both fat body and plasma during each of these peaks, the exception being the retention of high fat body JHE activity, when plasma JHE activity had dropped after the second peak; by contrast, in M. sexta, there was only a single peak in fat body JHE activity that strongly paralleled the first plasma JHE activity peak (Jesudason et al, 1992).…”

“…These results are similar to those reported for lepidopterans where high JHE activity occurs in fat body, and where fat body and plasma JHE activity developmental profiles were, in general, strongly correlated. This was especially the case for Trichoplusia ni (Wing et al, 1981;Hammock, 1985), and to a lesser degree for M. sexta (Jesudason et al, 1992). In contrast to the single JHE plasma activity peak during development in hemimetabolous insects such as G. assimilis, holometabolous insects have two plasma JHE activity peaks.…”

“…In the present study, we measured specific activities of JHE, as well as JH-epoxide hydrolase (JHEH), the other main JH-degrading enzyme, in fat body and midgut, throughout the last nymphal stadium in genetic stocks of Gryllus assimilis artificially selected for high-or low-plasma JHE activity. These tissues, especially fat body, were chosen since they exhibit high JHE specific activity and are likely major contributors to plasma JHE activity (Wing et al, 1981;Hammock, 1985;Roe and Venkatesh, 1990;Jesudason et al, 1992). In addition, using a recently obtained Jhe cDNA sequence from G. assimilis (Crone et al, 2007), we measured Jhe transcript abundance in both fat body and midgut.…”

Characterization of the juvenile hormone epoxide hydrolase (JHEH) and juvenile hormone diol phosphotransferase (JHDPT) from Manduca sexta Malpighian tubules

“…sexta (Vince and Gilbert, 1977;Baker et al, 1987;Jesudason et al, 1992). While total JH catabolism increases during the course of the last larval instar, the domination of JHEH over JHE in the first two days of this instar has been observed here and in earlier studies (Wisniewski et al, 1986;Jesudason et al, 1992). Baker et al (1987) reported that in vivo titers of JH I and JH I1 in last instar M. sexta decline from high levels on day 0 to barely detectable levels by day 1.5.…”