Phospho-regulated Drosophila adducin is a determinant of synaptic plasticity in a complex with Dlg and PIP2 at the larval neuromuscular junction.

Adducin is a ubiquitously expressed actin- and spectrin-binding protein involved in cytoskeleton organization, and is regulated through phosphorylation of the myristoylated alanine-rich C-terminal kinase (MARCKS)-homology domain by protein kinase C (PKC). We have previously shown that the Drosophila adducin, Hu-li tai shao (Hts), plays a role in larval neuromuscular junction (NMJ) growth. Here, we find that the predominant isoforms of Hts at the NMJ contain the MARCKS-homology domain, which is important for interactions with Discs large (Dlg) and phosphatidylinositol 4,5-bisphosphate (PIP2). Through the use of Proximity Ligation Assay (PLA), we show that the adducin-like Hts isoforms are in complexes with Dlg and PIP2 at the NMJ. We provide evidence that Hts promotes the phosphorylation and delocalization of Dlg at the NMJ through regulation of the transcript distribution of the PAR-1 and CaMKII kinases in the muscle. We also show that Hts interactions with Dlg and PIP2 are impeded through phosphorylation of the MARCKS-homology domain. These results are further evidence that Hts is a signaling-responsive regulator of synaptic plasticity in Drosophila.

Presynaptic gain control drives sweet and bitter taste integration in Drosophila.

The sense of taste is critical in determining the nutritional suitability of foods. Sweet and bitter are primary taste modalities in mammals, and their behavioral relevance is similar in flies. Sweet taste drives the appetitive response to energy sources, whereas bitter taste drives avoidance of potential toxins and also suppresses the sweet response [1, 2]. Despite their importance to survival, little is known about the neural circuit mechanisms underlying integration of sweet and bitter taste. Here, we describe a presynaptic gain control mechanism in Drosophila that differentially affects sweet and bitter taste channels and mediates integration of these opposing stimuli. Gain control is known to play an important role in fly olfaction, where GABAB receptor (GABABR) mediates intra- and interglomerular presynaptic inhibition of sensory neuron output [3-5]. In the taste system, we find that gustatory receptor neurons (GRNs) responding to sweet compounds express GABABR, whereas those that respond to bitter do not. GABABR mediates presynaptic inhibition of calcium responses in sweet GRNs, and both sweet and bitter stimuli evoke GABAergic neuron activity in the vicinity of GRN axon terminals. Pharmacological blockade and genetic reduction of GABABR both lead to increased sugar responses and decreased suppression of the sweet response by bitter compounds. We propose a model in which GABA acts via GABABR to expand the dynamic range of sweet GRNs through presynaptic gain control and suppress the output of sweet GRNs in the presence of opposing bitter stimuli.

Case report: the occurrence of fibrillary lines in overnight orthokeratology.

BACKGROUND: To report the occurrence of concentric fibrillary lines in the central corneas of a 13-year-old girl during overnight orthokeratology. METHODS: Observational case report. RESULTS: The initial refractive errors and keratometric readings (flattest/steepest meridians) of the patient were -6.00/-0.50 x 180 and 45.25/46.20 D, respectively, in the right eye and -5.50 DS and 44.90/45.80 D, respectively in the left eye. She underwent orthokeratology for myopic control, with a target reduction of 4.00 D myopia. A pair of DreimLens lenses was prescribed to be worn on a nightly basis and spectacles were worn by day. The same orthokeratology lenses were used throughout the monitoring period. Corneal topography showed well-centred treatment zones but persistent peripheral corneal staining due to trichiasis. A faint, peripheral pigmented brownish corneal arc and bundles of fine concentric fibrillary lines were observed in the central cornea about 12 months after commencing lens wear. In view of the persistent corneal staining due to trichiasis, she was advised to stop the orthokeratology treatment after 16 months of lens wear and was prescribed 1-Day Acuvue daily disposable contact lenses. The pigmented line disappeared after 2 months of hydrogel lens wear, while the fibrillary lines took 10 months to resolve. CONCLUSIONS: Fibrillary lines are a feature of the normal cornea thought to represent the arrangement of the subbasal, epithelial nerve plexus. We hypothesize that orthokeratology lens wear stimulates an altered epithelial migration pattern and a structural reorganisation of the subbasal nerve plexus in relation to this. This is assumed to account for the concentric pattern of fibrillary lines seen in our patient. The lines had no effect on vision and resolved over a period of 10 months following cessation of orthokeratology lens wear.

Drosophila RhoGAP68F is a putative GTPase activating protein for RhoA participating in gastrulation.

The Rho family small GTPases Rho, Rac, and Cdc42 regulate cell shape and motility through the actin cytoskeleton. These proteins cycle between a GTP-bound "on" state and a GDP-bound "off" state and are negatively regulated by GTPase-activating proteins (GAPs), which accelerate the small GTPase's intrinsic hydrolysis of bound GTP to GDP. Drosophila RhoGAP68F is similar to the mammalian protein p50RhoGAP/Cdc42GAP, which exhibits strong GAP activity toward Cdc42. We find that, despite the strong similarities between RhoGAP68F and p50RhoGAP/Cdc42GAP, RhoGAP68F is most effective as a GAP for RhoA. These in vitro data are supported by the in vivo analysis of mutants in RhoGAP68F. We demonstrate through the characterization of two alleles of the RhoGAP68F gene that RhoGAP68F participates in gastrulation of the embryo, a morphogenetic event driven by cell constriction that involves RhoA signaling. We propose that RhoGAP68F functions as a regulator of RhoA signaling during gastrulation.