Modulation of dopamine‐dependent behaviors by the Caenorhabditis elegans Olig homolog HLH‐17

Abstract

In vertebrates and invertebrates, dopamine signaling modulates a wide variety of physical and behavioral functions and exerts these effects through heterotrimeric G proteins. The soil nematode Caenorhabditis elegans has been used to model dopamine signaling and reacts reproducibly to alterations in dopamine levels through eight well-characterized dopaminergic neurons located in the head. In C. elegans, the basic helix-loop-helix transcription factor HLH-17 is strongly and constitutively expressed in the glia cells that ensheath four of the dopaminergic neurons, yet it is not required for specification or development of either the glia or the neurons. In this study, we sought to determine whether HLH-17 functions in dopamine signaling. We found that, unlike wild-type animals, hlh-17 animals are resistant to the effects of exogenous dopamine on egg laying and mobility. hlh-17 animals are also defective in the basal slowing and gustatory plasticity behaviors that require functional dopamine signaling. We also found that the expression of the dopamine receptor genes dop-1, dop-2, and dop-3 and the RGS protein gene egl-10 is significantly reduced in hlh-17 animals. Together these results point to a role for HLH-17 in dopamine signaling in C. elegans.

Dopamine Signaling inC. elegansIs Mediated in Part by HLH-17-Dependent Regulation of Extracellular Dopamine Levels

“…Total RNA, cDNA synthesis, and real-time PCR were performed as previously described (Felton and Johnson 2011), except the cDNA was amplified from 1 µg of total RNA in 20 µL reactions. Real-time PCR was performed with Taqman Gene Expression Assays (Applied Biosystems/Invitrogen) using relative quantitation against glyceraldehyde 3-phosphate dehydrogenase ( gpd-3 ) (Ce02616909_gH) as the endogenous control.…”

“…Assays for dopamine paralysis and basal slowing response were as previously described (Felton and Johnson 2011), except animals were assayed at the late L4 stage. For SWIP, approximately 10 L4-stage animals were placed in 150 µL of water in a single well of 48-well tissue culture plate (Cat #677180; CELLSTAR).…”

“…HLH-17 is the C. elegans homolog of the mammalian proneural family Olig (Ligon et al 2006; Zhou and Anderson 2002) but does not appear to play a role in neuronal specification during embryogenesis (Yoshimura et al 2008). Our previous studies instead demonstrated that HLH-17 is required for normal behavioral responses to dopamine signaling (Felton and Johnson, 2011). …”

“…Our previous data revealed that HLH-17 affects dopamine signaling through the DOP-1, DOP-2, and DOP-3 receptors as shown by the impaired response of hlh-17(ns204) animals to endogenous and exogenous dopamine. The hlh-17(ns204) animals also have reduced levels of the dop-3 and dop-1 mRNAs and phenocopy dop-3 hypomorhs (Chase et al 2004; Felton and Johnson 2011). Together, these data suggest that HLH-17 functions upstream of the dopamine receptor genes and that the loss of hlh-17 causes a reduction in dopamine receptor activity.…”

IGDB-2, an Ig/FNIII protein, binds the ion channel LGC-34 and controls sensory compartment morphogenesis in C. elegans

“…Glial loss or manipulation in this animal leads to profound sensory and synaptic deficits (Bacaj et al, 2008; Colón-Ramos et al, 2007; Felton and Johnson, 2011; Singhvi et al, 2016; Wallace et al, 2016). Importantly, interactions between single glia and neurons can be interrogated at the level of neuronal activity and animal behavior (Oikonomou and Shaham, 2011).…”