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Patrick William Keeley, Jason J Kim, Benjamin E Reese; Variation in mosaic patterning in the mouse retina: from regular to random.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2224. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal neurons of the same type are commonly assumed to be distributed as regular arrays known as mosaics, but relatively few different types have been thoroughly assessed. To determine the generality of mosaic regularity in the retina, the present study has analyzed the spatial organization of six different cell types, including the horizontal cells (HCs), two types of amacrine cells (ACs), and three types of cone bipolar cells (CBCs).
Adult mouse retinas from the A/J strain were immunolabeled to identify the populations of HCs, VGluT3+ (VG3) ACs, cholinergic (ChAT) ACs, and Types 2, 3b and 4 CBCs. Eight fields from each wholemount retina were sampled to identify the X-Y coordinates of each cell body, from which the Delauney tessellation and the spatial autocorrelation of each field were computed. Various spatial properties of the mosaics were then calculated, and compared to those from simulations of random mosaics matched in density and constrained by soma size.
The VG3 AC mosaics, as well as the mosaics from the three CBC types, were found to be conspicuously less regular and less efficiently packed than the mosaics of the HCs or ChAT ACs. Despite their lesser order, the VG3 ACs were still discriminable from random distributions, while the three CBC mosaics, however, had spatial properties that were comparable to such distributions. Critically, when their spatial properties were considered as a function of the variation in cellular density across fields, all types of CBCs behaved similar to random simulations, whereas the HCs and ChAT ACs spaced themselves apart more uniformly, evidenced by a strong significant negative correlation between the effective radius and cell density. VG3 ACs, while having comparable densities to the HCs in the A/J mouse retina, do not space themselves apart uniformly, thereby exhibiting reduced regularity and packing.
The positioning of CBCs in a mosaic is constrained only by the physical size of their somata, rendering their mosaics irregular to the point of being random. VG3 ACs, by contrast, fail to come into contact with one another as frequently as a random simulation would predict, yet they do not modulate their intercellular spacing uniformly with all of their homotypic neighbors. HCs and ChAT ACs exhibit the critical hallmark of regular retinal mosaics, minimizing proximity to all of their near neighbors.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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