Isoprenoids Control Germ Cell Migration Downstream of HMGCoA Reductase

Abstract

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAr) provides attractive cues to Drosophila germ cells, guiding them toward the embryonic gonad. However, it remains unclear how HMGCoAr mediates this attraction. In a genomic analysis of the HMGCoAr pathway, we found that the fly genome lacks several enzymes required for cholesterol biosynthesis, ruling out cholesterol and cholesterol-derived proteins as mediators of PGC migration. Genetic analysis of the pathway revealed that two enzymes, farnesyl-diphosphate synthase and geranylgeranyl-diphosphate synthase, required for the production of isoprenoids, act downstream of HMGCoAr in germ cell migration. Consistent with a role in geranylgeranylation, embryos deficient in geranylgeranyl transferase type I show germ cell migration defects. Our data, together with similar findings in zebrafish, implicate an isoprenylated protein in germ cell attraction. The specificity and evolutionary conservation of the HMGCoAr pathway for germ cells suggest that an attractant common to invertebrates and vertebrates guides germ cells in early embryos.

Transcriptional Control of Cholesterol Biosynthesis in Schwann Cells by Axonal Neuregulin 1

“…Most interestingly, the sea squirt is also unable to form myelin (31). While searching the genomes of other invertebrate nonchordates, for which a complete genomic sequence is available, we found that all of them lacked several fundamental genes of the sterol branch of the mevalonate pathway, supporting the data obtained by other authors (32). The search included arthropods like Drosophila melanogaster and Anopheles gambiae, and the nematode Caenorhabditis elegans.…”

Insect juvenile hormone action as a potential target of pest management

“…Importantly, insects and other arthropods do not synthesize cholesterol de novo but have to acquire it from dietary sources because they lack the genes encoding squalene synthase and other subsequent enzymes of the sterol branch. 28,29) Another peculiarity of the mevalonate pathway in insects is the capacity to synthesize JH via the isoprenoid branch.…”

“…Importantly, insects and other arthropods do not synthesize cholesterol de novo but have to acquire it from dietary sources because they lack the genes encoding squalene synthase and other subsequent enzymes of the sterol branch. 28,29) Another peculiarity of the mevalonate pathway in insects is the capacity to synthesize JH via the isoprenoid branch.The genes encoding the enzymes in the mevalonate pathway from acetyl-CoA to farnesyl diphosphate have been identified in the genome of D. melanogaster and the malaria mosquito Anopheles gambiae, and in an EST library of the pine engraver Ips pini.27) However, it has been difficult to identify the genes encoding enzymes from farnesyl diphosphate to JH …”

In vivo analysis of compound activity and mechanism of action using epistasis in Drosophila

“…Since there is no cholesterol biosynthesis in Drosophila and 7-dehydrocholesterol Δ 7 reductase (DHCR7), the enzyme targeted by AY9944, is not present [37], we reasoned that the inhibition of the Hh pathway in Drosophila by AY9944 must be mediated by its effects on cholesterol trafficking. AY9944 treatment of mammalian cells leads to the intracellular accumulation of free cholesterol, which can be detected by the fluorescent dye filipin [45].…”

“…While the inhibitory effect of AY9944 on Hh signaling has been attributed to both its ability to inhibit cholesterol biosynthesis and trafficking of exogenously derived cholesterol, these pleiotropic effects on cholesterol metabolism hindered a clear understanding of its mechanism of action on Hh signaling [10,22,28]. The absence of cholesterol biosynthesis in Drosophila [37] provided us with a unique opportunity to separate the effects of AY9944 on cholesterol biosynthesis and trafficking and to study the mechanism of its inhibition of Hh signaling in the absence of cholesterol synthesis. Our genetic characterization of the mechanism of action of this compound revealed that AY9944 inhibits Hh-induced Ptc internalization, an immediate consequence of Hh binding to Ptc, as well as the expression of the Hh target gene engrailed (en).…”