The cellular and molecular mechanisms responsible for the development of inner retinal circuitry are poorly understood. Reelin and apolipoprotein E (apoE), ligands of apoE receptor 2 (ApoER2), are involved in retinal development and degeneration, respectively. Here we describe the function of ApoER2 in the developing and adult retina. ApoER2 expression was highest during postnatal inner retinal synaptic development and was considerably lower in the mature retina. Both during development and in the adult ApoER2 was expressed by A-II amacrine cells. ApoER2 knockout (KO) mice had rod bipolar morphogenic defects, altered A-II amacrine dendritic development, and impaired rod-driven retinal responses. The presence of an intact ApoER2 NPxY motif, necessary for binding disabled-1 (Dab1) and transducing the Reelin signal, was also necessary for development of the rod bipolar pathway while the alternatively-spliced exon19 was not. Mice deficient in another Reelin receptor, very low-density lipoprotein receptor (VLDLR), had normal rod bipolar morphology but altered A-II amacrine dendritic development. VLDLR KO mice also had reductions in oscillatory potentials and delayed synaptic response intervals. Interestingly, age-related reductions in rod and cone function were observed in both ApoER2 and VLDLR KOs. These results support a pivotal role for ApoER2 in the establishment and maintenance of normal retinal synaptic connectivity.
Quantum dot (Qdot) biosensors have consistently provided valuable information to researchers about cellular activity due to their unique fluorescent properties. Many of the most popularly used Qdots contain cadmium, posing the risk of toxicity that could negate their attractive optical properties. The design of a non-cytotoxic probe usually involves multiple components and a complex synthesis process. In this paper, the design and synthesis of a non-cytotoxic Qdot-chitosan nanogel composite using straight-forward cyanogen bromide (CNBr) coupling is reported. The probe was characterized by spectroscopy (UV-Vis, fluorescence), microscopy (Fluorescence, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Dynamic Light Scattering. This activatable OPEN ACCESS Nanomaterials 2015, 5 2360 ("OFF"/"ON") probe contains a core-shell Qdot (CdS:Mn/ZnS) capped with dopamine, which acts as a fluorescence quencher and a model drug. Dopamine capped "OFF" Qdots can undergo ligand exchange with intercellular glutathione, which turns the Qdots "ON" to restore fluorescence. These Qdots were then coated with chitosan (natural biocompatible polymer) functionalized with folic acid (targeting motif) and Fluorescein Isothiocyanate (FITC; fluorescent dye). To demonstrate cancer cell targetability, the interaction of the probe with cells that express different folate receptor levels was analyzed, and the cytotoxicity of the probe was evaluated on these cells and was shown to be nontoxic even at concentrations as high as 100 mg/L.
Semiconductor fluorescent quantum dots (Qdots) are popularly used as bioimaging taggants in live cell imaging and spectroscopy. In recent years, Qdots taggants are emerging in agricultural applications. Studies are primarily focused on nanotoxicity of ultra-small size water-soluble Qdots in plant systems. Nanotoxicity is correlated with Qdot core composition and surface coating. However, Qdots with certain chemical composition and surface coating may boost plant growth. In this study, we report that N-acetyl cysteine (NAC) capped ∼3.5 nm size ZnS:Mn/ZnS Qdots (NAC-Qdot) are efficiently uptaken by the snow pea (Pisum sativum L., a model plant) vascular system, enhancing the root growth at a dose level of 80 μg/mL. Fluorescence microscopy studies confirmed localization of NAC-Qdots in the intercellular regions. Germination and growth of the snow pea seeds were found to be strongly dependent on Qdot dosage and incubation time with Qdots. Seed germination reached 100% within 48 hours of NAC-Qdot exposure. Based on our preliminary findings, it is suggested that NAC-Qdot can be used as systemic plant nutrient material for boosting the seed germination and plant growth.
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