Logic gate behavior and intracellular application of a fluorescent molecular switch for the detection of Fe3+ and cascade sensing of F- in pure aqueous media.

The nature and coordination sites of the Schiff base 3,3'-(1E,1'E)-(1,3-phenylenebis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol (APHN) were tuned by its selective reduction to design a highly efficient fluorescent probe, 3,3'-(pyridine-2,6-diylbis(azanediyl))bis(methylene)dinaphthalen-2-ol (RAPHN). The structures of APHN, RAPHN, and the RAPHN-Fe3+ complex were satisfactorily modeled from the results of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. RAPHN worked in pure aqueous medium as a turn on-off-on probe of Fe3+ and F-. The fluorescence nature of the probe in the presence and absence of Fe3+/F- was regulated by a set of mechanisms including -CH[double bond, length as m-dash]N isomerization and LMCT. A 2 : 1 (M : L) binding stoichiometry was established from a fluorescence Job's plot and further substantiated from HR-MS studies. The limits of detection of RAPHN for Fe3+ and RAPHN-Fe3+ for F- were found to be 2.49 × 10-7 M and 1.09 × 10-7 M, respectively. The RAPHN probe caused no cytotoxicity in gut tissue of Drosophila even at high concentrations. The probe displayed excellent bioimaging applications for detection of Fe3+ and F- in gut tissue of Drosophila. A combinatorial logic gate was constructed for the proper understanding of the working principle of RAPHN.

Modelling TDP-43 proteinopathy in Drosophila uncovers shared and neuron-specific targets across ALS and FTD relevant circuits.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) comprise a spectrum of neurodegenerative diseases linked to TDP-43 proteinopathy, which at the cellular level, is characterized by loss of nuclear TDP-43 and accumulation of cytoplasmic TDP-43 inclusions that ultimately cause RNA processing defects including dysregulation of splicing, mRNA transport and translation. Complementing our previous work in motor neurons, here we report a novel model of TDP-43 proteinopathy based on overexpression of TDP-43 in a subset of Drosophila Kenyon cells of the mushroom body (MB), a circuit with structural characteristics reminiscent of vertebrate cortical networks. This model recapitulates several aspects of dementia-relevant pathological features including age-dependent neuronal loss, nuclear depletion and cytoplasmic accumulation of TDP-43, and behavioral deficits in working memory and sleep that occur prior to axonal degeneration. RNA immunoprecipitations identify several candidate mRNA targets of TDP-43 in MBs, some of which are unique to the MB circuit and others that are shared with motor neurons. Among the latter is the glypican Dally-like-protein (Dlp), which exhibits significant TDP-43 associated reduction in expression during aging. Using genetic interactions we show that overexpression of Dlp in MBs mitigates TDP-43 dependent working memory deficits, conistent with Dlp acting as a mediator of TDP-43 toxicity. Substantiating our findings in the fly model, we find that the expression of GPC6 mRNA, a human ortholog of dlp, is specifically altered in neurons exhibiting the molecular signature of TDP-43 pathology in FTD patient brains. These findings suggest that circuit-specific Drosophila models provide a platform for uncovering shared or disease-specific molecular mechanisms and vulnerabilities across the spectrum of TDP-43 proteinopathies.