Systemic delivery of AAV9 offers the potential for widespread and efficient gene delivery to the retina, and may thus be a useful approach for treatment of disease where intraocular injections are not possible, for syndromes affecting multiple organs, or where early intervention is required. The expression resulting from intravenous injection of AAV9 is more efficient in neonates than adults, and here we characterize the effect of age on retinal transduction of AAV9 in the mouse retina. We find that the pattern of expression in neonatal mice is correlated to the development of the retinal vasculature, and that the area of the retinal transduction as well as the cell types infected vary depending on the age at injection. Furthermore, we demonstrate that sequential injections of AAV9 vectors carrying two different transgenes infect adjacent areas of the retina, providing a larger area of coverage. Lastly, we show that the retina's endogenous spatiotemporal expression pattern of Mfsd2a, a protein associated with the maturation of a functional blood-brain barrier, coincides with suppression of retinal transduction by intravenously-delivered AAV9, suggesting that AAV9 crosses the blood-retina barrier through transcytosis.
Many wingless insects perform directed aerial descent (DAD) to return to vegetational structures after falling. Given the complex visual environment and spatial structures of tree canopies, those visual signals used as directional cues are not fully understood. Here, we address the role of visual contrast for DAD in newly hatched nymphs of the stick insect Extatosoma tiaratum under controlled laboratory conditions. Landing preferences of gliding E. tiaratum in various visual environments were studied. We used a single vertical stripe defined by variable contrast edges to test the use of contrast consistency and sharpness. We also used aggregate patterns to examine the effects of target size and the effectiveness of luminance contrast and chromatic contrast. E. tiaratum nymphs were attracted to single stripes with welldefined edges, and particularly favored narrow dark targets. The directionality and accuracy of landing were dependent on target size. Lastly, luminance contrasts were more effective in attracting landings than were chromatic contrasts. Visual contrasts are therefore used as spatial references for landing behavior in DAD. These behaviors may enable nymphs to quickly locate dark or shaded sides of vertically oriented vegetation in natural habitats.
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