Efficient
Lam1 coating was obtained as the Lam1-coated beads clumped together and formed aggregates, which was not seen for BSA or uncoated beads, and confirmed by strong Lam1 staining by immunofluorescence. Bead implantations were performed by mounting 24 hpf embryos in 2%–4% methylcellulose (Sigma), containing 0.4 mg/ml MS222 (Sigma) as anesthetic. Beads were suspended in the methylcellulose, sucked into a sharp glass capillary connected to a mineral-oil filled Hamilton syringe, and injected into the retina of Akt inhibitor the embryo. Embryos were then transferred to clean Petri dishes containing embryo medium and penicillin/streptomycin/fungicide to recover. The polychromatic red dye showed extremely bright fluorescence, and the signal bleedthrough into the green channel was strong enough for bead visualization in most experiments. When imaging in red channel was also necessary, beads were photobleached by being placed on the windowsill for 2–4 weeks. Dissociated retinal cell culture was performed as previously described (Zolessi et al., 2006). For the creation of a substrate with Laminin islands, coverslips were coated
overnight with Venetoclax poly-L-lysine (Sigma, 10 μg/ml), and then sprayed with an atomizer creating a fine mist of Lam1 (Sigma, 20 μg/ml) mixed with Texas-red-conjugated Dextran (D-1863, Invitrogen) in order to stain the Laminin deposits. Imaging of live and fixed embryos was performed as described previously (Poggi et al., 2005), using a Perkin Elmer Spinning Disk UltraVIEW ERS, Olympus IX81 Inverted microscope and 60× (1.2 NA) water immersion objective, and a motorized XY stage (H117,
Prior) to allow for simultaneous imaging of multiple embryos. A confocal laser scanning microscope (Leica) and 63× (1.2 NA) water immersion objective (Leica) were also used for experiments shown in 3A–3C and 6B. Optical sections at 0.75–1 μm separation were taken to cover the majority of the retina (between 40 and 100 μm) at the relevant time intervals. Whole-mount immunostaining was performed using standard methods, using rabbit polyclonal anti-Lam1 (L9393, Sigma, 1:100) and anti-rabbit Alexa-594 (Invitrogen, 1:1000). Confocal data was analyzed using Volocity (Improvision). Deconvolution was generally performed on Interleukin-11 receptor data acquired by spinning disk confocal microscopy using the Iterative Restoration tool at 25 iterations and 99.99% confidence levels. Unless otherwise stated, the confocal z-slices were cropped to a rectangular region containing the cells of interest in XYZ and reconstructed using 3D Opacity. Brightness, contrast, and gamma were adjusted for maximal visibility of cellular morphology and fluorescent signal using Volocity, Photoshop (Adobe), and ImageJ (NIH), and the RFP channel was converted to magenta using the channels tool in ImageJ. Pseudocoloring and cell tracing was done in Photoshop, and the outline of the cell was determined by comparing it to the original confocal z-slices.