Control of Antagonistic Components of the Hedgehog Signaling Pathway by microRNAs in Drosophila

Abstract

Hedgehog (Hh) signaling is critical for many developmental processes and for the genesis of diverse cancers. Hh signaling comprises a series of negative regulatory steps, from Hh reception to gene transcription output. We previously showed that stability of antagonistic regulatory proteins, including the coreceptor Smoothened (Smo), the kinesin-like Costal-2 (Cos2), and the kinase Fused (Fu), is affected by Hh signaling activation. Here, we show that the level of these three proteins is also regulated by a microRNA cluster. Indeed, the overexpression of this cluster and resulting microRNA regulation of the 39-UTRs of smo, cos2, and fu mRNA decreases the levels of the three proteins and activates the pathway. Further, the loss of the microRNA cluster or of Dicer function modifies the 39-UTR regulation of smo and cos2 mRNA, confirming that the mRNAs encoding the different Hh components are physiological targets of microRNAs. Nevertheless, an absence of neither the microRNA cluster nor of Dicer activity creates an hh-like phenotype, possibly due to dose compensation between the different antagonistic targets. This study reveals that a single signaling pathway can be targeted at multiple levels by the same microRNAs.

microRNA control of cell-cell signaling during development and disease

“…53 This study showed that multiple transcripts that encode members of a multicomponent cytoplasmic complex in the Hh pathway were directly repressed by miR-12 and/or miR-283, including costal-2, smoothened and fused. These were demonstrated as endogenous targets since imaginal disc cells lacking the miRNA cluster exhibited modestly increased levels of transgenic 3'UTR sensors for these target genes.…”

“…Nevertheless, this was insufficient to lead to a phenotypic defect in Hh pathway output in miRNA mutant cells. 53 Possibly the miRNAs are required only for fine-tuning signaling. On the other hand, since Costal-2 and Smoothened are antagonistically-acting components of the Hh pathway, it is conceivable that the miRNA deletion situation represents an intermediate, phenotypically suppressed condition.…”

The Ataxin-2 protein is required for microRNA function and synapse-specific long-term olfactory habituation

“…To understand why the costal-2 reporter could be insensitive to GW182 (or Atx2) knockdown, we examined the sequence of its 3′ UTR and found it to contain not only target sites for miR12 and miR283, as reported earlier (38), but also two binding sites for miR277. This finding is significant because, unlike the majority of Dcr1-dependent miRNAs, miR277 is loaded preferentially onto Ago2-RISC complexes because of the extensive basepairing between its miRNA and miRNA* strands (40)(41)(42).…”

“…4 B and B′) reporters. Given that the latter two reporters are regulated by artificial UTRs engineered to be repressed solely through the miRNA pathway (37,38), these data strongly argue that Atx2 is broadly required for miRNA function.…”

mir-35 is involved in intestine cell G1/S transition and germ cell proliferation in C. elegans

“…It remains to be seen elusive if such a regulatory scheme of a miR-NA family applies to all multi-cell organisms. At least in D. melanogaster, a miRNA cluster is found to impair hedgehog signaling [66].…”