Troy, C. M. | Search bioRxiv

bioRxiv2022

CyclinD2-mediated regulation of neurogenic output from the retinal ciliary margin is perturbed in albinism

In albinism, aberrations in the ipsi-/contralateral retinal ganglion cell (RGC) ratio compromise the functional integrity of the binocular circuit. We focus here on the mouse ciliary margin zone (CMZ), a neurogenic niche at the embryonic peripheral retina, to investigate developmental processes regulating RGC neurogenesis and identity acquisition. We found that the mouse ventral CMZ has the competence to generate predominantly ipsilaterally-projecting RGCs, but this competence is altered in the albino visual system due to CyclinD2 downregulation and disturbed temporal control of the cell cycle. Consequently, albino as well as CyclinD2-deficient pigmented mice exhibit a diminished ipsilateral retinogeniculate projection and compromised depth perception. Pharmacological stimulation of calcium channels in albino mice, known to upregulate CyclinD2 in other cell types, augmented CyclinD2-dependent neurogenesis of ipsilateral RGCs, and improved stereopsis. Together, these results implicate CMZ neurogenesis and its regulators as critical for the formation and function of the mammalian binocular circuit. HighlightsO_LIThe mouse ventral CMZ produces predominantly ipsilateral RGCs. C_LIO_LIIn the albino visual system, CyclinD2 downregulation leads to delayed G1/S transition toward mitotic exit of CMZ progenitors. C_LIO_LIPerturbations in the temporal control of cell cycle by CyclinD2 lead to reduced Zic2+ RGCs and consequently, a diminished ipsilateral retinogeniculate projection and compromised depth perception. C_LIO_LICalcium channel modulation during embryogenesis normalizes the levels of CyclinD2 and restores binocular vision in albino mice. C_LI

developmental biology↗

bioRxiv2021

Optimizing touchscreen measures of rodent cognition by eliminating image bias

For the last twenty years, the Bussey-Saksida touchscreen-based operant conditioning platform has evolved in close parallel alongside the Cambridge Neuropsychological Test Automated Battery (CANTAB) to produce batteries of tests for studying complex cognitive functions in rodents that are increasingly analogous to human diagnostic tests and greatly narrow the translational gap in cognition research. Naturally, with this increasing usefulness comes increasing use, particularly by non-experts. This necessitates a greater understanding of, and a better controlling for, confounding factors that may limit the systems ability to optimally detect cognitive deficits when used as a widely accessible and commercially available standardized task. In the present study, we show a strong image preference bias in a standard pairwise discrimination task with a widely used spider-plane image pairing in a putative animal model for intellectual disability. This bias greatly influenced the performance of our experimental mice, significantly affecting the length of time it took mice to complete the task, their progress over time, and several accessory measures usefully recorded by the Bussey-Saksida touchscreen system. We further show that this bias can be corrected by using more similar image pairings without sacrificing the animals ability to learn to distinguish the stimuli. This approach eliminated all significant stimuli specific differences seen with the spider-plane pairing. We then analyzed the pixel composition of the various stimuli to suggest that the bias is due to a difference in image brightness. These findings highlight the importance of carefully modulating paired touchscreen stimuli to ensure equivalence prior to learning and the need for more studies of visual perception in mice, particularly as it relates to their performance in cognitive assays.

animal behavior and cognition↗