Variations in ecdysteroid titers play crucial roles in arthropods by initiating and regulating molting and metamorphosis. The recent identification of genes coding for cytochrome P450 enzymes involved in Drosophila ecdysteroidogenesis provides new molecular tools to investigate the regulation of insect hormone production. In the present study, we used an enzyme immunoassay to show that the molting hormone titer is strictly correlated with the steroidogenic capacity of the ring gland. A temporal correlation between dynamics of ecdysone production and expression of genes encoding steroidogenic enzymes was observed during the third instar, suggesting that the timing of hormone production depends on transcriptional regulation of the biosynthetic enzymes. Using clonal analysis, levels of two steroidogenic enzymes, Phantom (PHM) and Disembodied (DIB), were shown to be very reduced in ftz transcription factor 1 (ftz-f1) mutant ring gland cells whereas there was no effect of the without children (woc) mutation, suggesting that FTZ-F1 regulates phm and dib expression. Since βFTZ-F1 is the homolog of the vertebrate steroidogenic factor 1 (SF1), which plays a key role in the differentiation of vertebrate steroidogenic organs through transcriptional regulation of steroidogenic enzymes, this study emphasizes the strong parallels between insects and vertebrates with respect to the regulatory mechanisms of steroidogenesis.
Bibliographical noteFunding Information:
We thank A. Hadfi for his help on synchronizing larvae, A. Maria for technical assistance, Drs. S. J. Kimber and I. J. H. Roberts for communication of unpublished data, Prof. R. Lafont and Dr. P. Fichelson for critical comments on the manuscript. This work is supported by the Université Pierre et Marie Curie and the Ministère de la Recherche Scientifique (for J.P.P., C.B., F.B. and C.D.V.). J.T.W. and L.I.G. were supported by National Science Foundation Grant IBN0130825. A.P. was supported by NIH Training Grant HD33692. M.B.O. is an Investigator of the Howard Hughes Medical Institute.
- Cytochrome P450
- Ring gland