Purpose
Many cell types and signaling pathways have been discovered which control development of the superficial plexus (SP), yet mechanisms describing how these vessels dive into the deeper portions of the retina to form the deep and intermediate plexi (DP, IP) are less explored. We tested the hypothesis that lamination of neurons within the inner retina is required for formation of the DP and IP by assaying retinal vasculature within knockout mouse models varying in lamination and density of neurons within the inner retina.
Methods
This study utilized 3 knockout mouse models to perturb neuron organization within the inner retina: Bax, Dscam and Fat3 mutant mice. Bax-/- retinas have increased neuron densities with limited disruption of neuron lamination. Dscam-/- retinas have increased neuron densities with highly disrupted neuron lamination. Fat3-/- retinas have normal neuron densities with abnormal neuron lamination. The plexus layers and vessels connecting the plexi were assayed in these mice at post natal day 28 (p28) and compared to WT controls. Vessels were labeled with GS isolectin (Alexa 568) and imaged using fluorescent confocal microscopy.
Results
An increase in vessel density was observed within Bax-/- retinas. Organization of the plexi and connecting vessels was maintained within Bax-/- and Fat3-/- retinas, with the exception that ectopic vessels were observed within the inner plexiform layer (IPL) and inner nuclear layer (INL), respectively. Organization of the SP and DP was maintained within Dscam-/- retinas, yet the connecting vessels were tortuous and the IP did not form. An increase in BPs was observed within the IPL of Bax-/- retinas, within the INL of Fat3-/- retinas, and throughout the IPL and INL of Dscam-/- retinas. A 30-fold increase in filopodia was observed within Dscam-/- retinas at p28.
Conclusions
Our results are consistent with our hypothesis that lamination of the inner retina is required for formation of the DP and IP during development of the retinal vasculature. This study also suggests that the soma/neurite boundary promotes branching of vessels as they dive into deeper portions of the retina.