Ecdysone C20-hydroxylation and conjugate formation by Drosophila melanogaster cell lines

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Visualization of chromosomal domains with boundary element-associated factor BEAF-32

We have purified two proteins from Drosophila that bind to the scs' boundary element of the hsp70 domain at locus 87A7. Their palindromic binding sites (CGATA-TATCG) symmetrically abut the previously mapped hypersensitive site of scs'. We have cloned a cDNA for one of these proteins, BEAF-32 (boundary element-associated factor of 32 kDa). It encodes a novel protein that is bound to scs' but not scs in vivo. Immunostaining localizes BEAF to hundreds of interbands and many puff boundaries on polytene chromosomes, suggesting that a chromosomal domain consists of a band (or puff) and part of the flanking interbands. Enhancer blocking assays implicate the palindromic binding site in boundary function. The lack of enhancer blocking in transiently transfected cells suggests an involvement of chromatin, nuclear structure, or both in boundary function.