A Drosophila behavioral mutant, down and out ( dao ), is defective in an essential regulator of Erg potassium channels

Abstract

To signal properly, excitable cells must establish and maintain the correct balance of various types of ion channels that increase or decrease membrane excitability. The mechanisms by which this balance is regulated remain largely unknown. Here, we describe a regulatory mechanism uncovered by a Drosophila behavioral mutant, down and out ( dao ). At elevated temperatures, dao loss-of-function mutants exhibit seizures associated with spontaneous bursts of neural activity. This phenotype closely resembles that of seizure mutations, which impair activity of ether-a-go-go-related gene (Erg)-type potassium channels. Conversely, neural over-expression of wild-type Dao confers dominant temperature-sensitive paralysis with kinetics reminiscent of paralytic sodium-channel mutants. The over-expression phenotype of dao is suppressed in a seizure mutant background, suggesting that Dao acts by an effect on Erg channels. In support of this hypothesis, functional expression of Erg channels in a heterologous system is dependent on the presence of Dao. These results indicate that Dao has an important role in establishing the proper level of neuronal membrane excitability by regulating functional expression of Erg channels.

The Enigmatic Cytoplasmic Regions of KCNH Channels

“…6A) 64 . Channels produced by sei expression in Xenopus oocytes lack the I Kr -like rectification of mammalian ERG channels and have fast deactivation, much like EAG channels 65 . Bioinformatics and functional analysis comparing Drosophila, C. elegans and sea anemone orthologs indicate the PAS domain sequence was present in an ancestral gene predating the divergence of the bilaterians and cnidarians, but degenerated at least twice during evolution 66 .…”

Functional evolution of Erg potassium channel gating reveals an ancient origin for I Kr

“…DmErg channels require coexpression with the cytosolic protein down and out (DAO) for plasma membrane trafficking (18). DAO is unique to Drosophila, but it contains a tetratricopeptide repeat (TPR domain), which is a widespread protein interaction motif (18). A TPR-containing protein has also been implicated in HsErg1 trafficking (24).…”

“…We reasoned that absence of functional expression could be due to impaired trafficking of channels to the plasma membrane. DmErg channels require coexpression with the cytosolic protein down and out (DAO) for plasma membrane trafficking (18). DAO is unique to Drosophila, but it contains a tetratricopeptide repeat (TPR domain), which is a widespread protein interaction motif (18).…”

“…1 A and B) and deactivates rapidly upon repolarization ( Fig. 1D) (18). The voltage-activation curve (GV) of DmErg is shifted to hyperpolarized potentials, suggesting influence on subthreshold excitability (Fig.…”

Differential effects of nitric oxide on the responsiveness of tactile hairs

“…It has been suggested that hERG potassium channels play a role in spike-frequency adaptation (Chiesa et al 1997). hERG-type potassium channels have also been found in Drosophila (Fergestad et al 2010), although it is not clear whether they are present in mechanosensory neurons, in particular.…”