Abstract
Steroid hormones are responsible for coordinating many aspects of biological processes in most multicellular organisms, including insects. Ecdysteroid, the principal insect steroid hormone, is biosynthesized from dietary cholesterol or plant sterols. In the last 20 years, a number of ecdysteroidogenic enzymes, including Noppera-bo, Neverland, Shroud, Spook/Spookier, Cyp6t3, Phantom, Disembodied, Shadow, and Shade, have been identified and characterized in molecular genetic studies using the fruit fly Drosophila melanogaster. These enzymes are encoded by genes collectively called the Halloween genes. The transcriptional regulatory network, governed by multiple regulators of transcription, chromatin remodeling, and endoreplication, has been shown to be essential for the spatiotemporal expression control of Halloween genes in D. melanogaster. In this review, we summarize the latest information on transcriptional regulators that are crucial for controlling the expression of ecdysteroid biosynthetic enzymes and their roles in insect development.
Highlights
Steroid hormones are bioactive small molecules that induce many physiological events in both vertebrates and invertebrates
During larval and pupal development, ecdysteroids are biosynthesized from dietary cholesterol and plant sterols in a special endocrine organ called the prothoracic gland (PG) (Figure 1)
Overexpression of any of the isoforms in the PG prevents larval molting or pupariation to varying degrees, which is consecutively rescued by administration of 20E (Zhou et al, 2004). These results suggest an inhibitory effect of Br-C on ecdysteroid biosynthesis in the PG
Summary
Steroid hormones are bioactive small molecules that induce many physiological events in both vertebrates and invertebrates. Studies have shown that loss of mld function in the PG impairs the expression of nvd and spok, but not that of other Halloween genes (Neubueser et al, 2005; Ono et al, 2006; Danielsen et al, 2014). Lossof-function mutations in séan or ouib result in a larval-arrest phenotype with a dramatic reduction in the expression of nvd and spok, respectively, but not in that of other Halloween genes.
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