Hymenopteran-specific TRPA channel from the Texas leaf cutter ant (Atta texana) is heat and cold activated and expression correlates with environmental temperature.

Leaf cutting ants of the genus Atta cultivate fungal gardens, carefully modifying environmental conditions to maintain optimal temperature for fungal growth. Antennal nerves from Atta are highly temperature sensitive, but the underlying molecular sensor is unknown. Here, we utilize Atta texana (Texas leaf cutter ant) to investigate the molecular basis of ant temperature sensation and how it might have evolved as the range expanded northeast across Texas from ancestral populations in Mexico. We focus on transient receptor potential (TRP) channel genes, the best characterized temperature sensor proteins in animals. Atta texana antennae express 6 of 13 Hymenopteran TRP channel genes and sequences are under a mix of relaxed and intensified selection. In a behavioral assay, we find A. texana workers prefer 24 °C (range 21-26 °C) for fungal growth. There was no evidence of regulatory evolution across a temperature transect in Texas, but instead Hymenoptera-specific TRPA (HsTRPA) expression highly correlated with ambient temperature. When expressed in vitro, HsTRPA from A. texana is temperature activated with Q10 values exceeding 100 on initial exposure to temperatures above 33 °C. Surprisingly, HsTRPA also appears to be activated by cooling, and therefore to our knowledge, the first non-TRPA1 ortholog to be described with dual heat/cold activation and the first in any invertebrate.

GRK2 Kinases in the Primary Cilium Initiate SMOOTHENED-PKA Signaling in the Hedgehog Cascade.

During Hedgehog (Hh) signal transduction in development and disease, the atypical G protein-coupled receptor (GPCR) SMOOTHENED (SMO) communicates with GLI transcription factors by binding the protein kinase A catalytic subunit (PKA-C) and physically blocking its enzymatic activity. Here we show that GPCR kinase 2 (GRK2) orchestrates this process during endogenous Hh pathway activation in the primary cilium. Upon SMO activation, GRK2 rapidly relocalizes from the ciliary base to the shaft, triggering SMO phosphorylation and PKA-C interaction. Reconstitution studies reveal that GRK2 phosphorylation enables active SMO to bind PKA-C directly. Lastly, the SMO-GRK2-PKA pathway underlies Hh signal transduction in a range of cellular and in vivo models. Thus, GRK2 phosphorylation of ciliary SMO, and the ensuing PKA-C binding and inactivation, are critical initiating events for the intracellular steps in Hh signaling. More broadly, our study suggests an expanded role for GRKs in enabling direct GPCR interactions with diverse intracellular effectors.

Divergent cis-regulatory evolution underlies the convergent loss of sodium channel expression in electric fish.

South American and African weakly electric fish independently evolved electric organs from muscle. In both groups, a voltage-gated sodium channel gene independently lost expression from muscle and gained it in the electric organ, allowing the channel to become specialized for generating electric signals. It is unknown how this voltage-gated sodium channel gene is targeted to muscle in any vertebrate. We describe an enhancer that selectively targets sodium channel expression to muscle. Next, we demonstrate how the loss of this enhancer, but not trans-activating factors, drove the loss of sodium channel gene expression from muscle in South American electric fish. While this enhancer is also altered in African electric fish, key transcription factor binding sites and enhancer activity are retained, suggesting that the convergent loss of sodium channel expression from muscle in these two electric fish lineages occurred via different processes.