rigor mortisencodes a novel nuclear receptor interacting protein required for ecdysone signaling duringDrosophilalarval development

Abstract

Pulses of the steroid hormone ecdysone trigger the major developmental transitions in Drosophila, including molting and puparium formation. The ecdysone signal is transduced by the EcR/USP nuclear receptor heterodimer that binds to specific response elements in the genome and directly regulates target gene transcription. We describe a novel nuclear receptor interacting protein encoded by rigor mortis (rig) that is required for ecdysone responses during larval development. rig mutants display defects in molting, delayed larval development, larval lethality, duplicated mouth parts, and defects in puparium formation – phenotypes that resemble those seen in EcR, usp, E75A and βFTZ-F1mutants. Although the expression of these nuclear receptor genes is essentially normal in rig mutant larvae, the ecdysone-triggered switch in E74 isoform expression is defective. rig encodes a protein with multiple WD-40 repeats and an LXXLL motif, sequences that act as specific protein-protein interaction domains. Consistent with the presence of these elements and the lethal phenotypes of rig mutants, Rig protein interacts with several Drosophila nuclear receptors in GST pull-down experiments, including EcR, USP, DHR3, SVP and βFTZ-F1. The ligand binding domain of βFTZ-F1 is sufficient for this interaction, which can occur in an AF-2-independent manner. Antibody stains reveal that Rig protein is present in the brain and imaginal discs of second and third instar larvae,where it is restricted to the cytoplasm. In larval salivary gland and midgut cells, however, Rig shuttles between the cytoplasm and nucleus in a spatially and temporally regulated manner, at times that correlate with the major lethal phase of rig mutants and major switches in ecdysone-regulated gene expression. Taken together, these data indicate that rig exerts essential functions during larval development through gene-specific effects on ecdysone-regulated transcription, most likely as a cofactor for one or more nuclear receptors. Furthermore, the dynamic intracellular redistribution of Rig protein suggests that it may act to refine spatial and temporal responses to ecdysone during development.

Gemin3Is an Essential Gene Required for Larval Motor Function and Pupation inDrosophila

“…rigor mortis is an essential gene, and mutants therein display significant larval lethality; animals that escape the initial wave of larval lethality are developmentally delayed and fail to pupate (Gates et al, 2004). These phenotypes are strikingly similar to those of the Smn F and Gemin3 alleles described in this work.…”

“…These phenotypes are strikingly similar to those of the Smn F and Gemin3 alleles described in this work. Thummel and colleagues have shown that rig/dGem5 interacts with several members of the ecdysone signaling pathway required for initiation of puparium formation (Gates et al, 2004). Mammalian Gemin5 is also involved in signal transduction (Kim et al, 2007).…”

The Competence Factor βFtz-F1 Potentiates Ecdysone Receptor Activity via Recruiting a p160/SRC Coactivator

“…Our present work reveals a novel mechanism of interaction among transcriptional regula-tors and a coactivator, which allows the functional integration of multiple transcriptional factors and enables the outputs of particular signaling pathways to be activated in a stage-specific manner. In recent years, several cofactors, including Bonus, NURF, Rig, SMRTER, Taiman, and TRR, have been implicated in ecdysone signaling during Drosophila development (1,2,4,12,38,43). In this study, we have shown that the coactivator FISC acts as a bridge between ␤Ftz-F1 and EcR/USP in the formation of the multiprotein complex, while there is no detectable direct physical attachment between ␤Ftz-F1 and EcR/USP.…”

Evolution of an RNP assembly system: A minimal SMN complex facilitates formation of UsnRNPs in Drosophila melanogaster

“…It is conceivable that Dhh1 and Rigor mortis have adopted novel functions in a different context because they rapidly diverge from their ancestors (28). Consistent with this notion, a function of Rigor mortis in ecdysone signaling has been described (29).…”