Development of ON and OFF cholinergic amacrine cells in the human fetal retina

Abstract

Choline acetyltransferase (ChAT) expressing retinal amacrine cells are present across vertebrates. These interneurons play important roles in the development of retinal projections to the brain and in motion detection, specifically in generating direction-selective responses to moving stimuli. ChAT amacrine cells typically comprise two spatially segregated populations that form circuits in the 'ON' or 'OFF' synaptic layers of the inner retina. This stereotypic arrangement is also found across the adult human retina, with the notable exception that ChAT expression is evident in the ON but not OFF layer of the fovea, a region specialized for high-acuity vision. We thus investigated whether the human fovea exhibits a developmental path for ON and OFF ChAT cells that is retinal location-specific. Our analysis shows that at each retinal location, human ON and OFF ChAT cells differentiate, form their separate synaptic layers, and establish non-random mosaics at about the same time. However, unlike in the adult fovea, ChAT immunostaining is initially robust in both ON and OFF populations, up until at least mid-gestation. ChAT expression in the OFF layer in the fovea is therefore significantly reduced after mid-gestation. OFF ChAT cells in the human fovea and in the retinal periphery thus follow distinct maturational paths.

Molecular Fingerprinting of On–Off Direction-Selective Retinal Ganglion Cells Across Species and Relevance to Primate Visual Circuits

“…Interestingly, there are also human-and macaque-specific adaptions in the distribution of SACs in the retina. In the adult human and macaque retina, there are dramatically fewer Offsublamina-stratifying SACs than there are On-sublaminastratifying SACs (Rodieck and Marshak, 1992;Yamada et al, 2005;Zhang et al, 2018). This is in stark contrast to the distribution of On and Off SACs in mice, which have a similar molecular signature to primate SACs (Zhang et al, 2018) but are found in relatively equal numbers.…”

“…In the adult human and macaque retina, there are dramatically fewer Offsublamina-stratifying SACs than there are On-sublaminastratifying SACs (Rodieck and Marshak, 1992;Yamada et al, 2005;Zhang et al, 2018). This is in stark contrast to the distribution of On and Off SACs in mice, which have a similar molecular signature to primate SACs (Zhang et al, 2018) but are found in relatively equal numbers. Importantly, the sparsity of Off SACs in humans and macaques can be extended to imply that, if On-Off DSGCs existed in these species, then the circuit underlying direction selectivity to negative contrast (the Off response component) is unlikely to rely on asymmetrical inhibition from Off-SACs, as has been reported in both mice and rabbits (Borst and Euler, 2011;Taylor and Smith, 2012;Vaney et al, 2012;Mauss et al, 2017).…”

“…The identification of markers of cell types has greatly advanced our understanding of the organization, development, and function of the nervous system, especially in primate species (Dacey et al, 2005;Lee et al, 2016;Chandra et al, 2017;Hannibal et al, 2017;Johnson et al, 2017;Zhang et al, 2018). We hypothesized that if On-Off DSGCs were conserved across species, then perhaps the genetic pathways that define this RGC type would also be conserved (schematized in Fig.…”

“…Although macaque monkeys diverged from mice and rabbits ϳ95 million years ago, many of the circuit elements that together form direction-selective retinal circuits in mice and rabbits are also present in the macaque retina. SACs, a type of cholinergic retinal interneuron, are critical for generating direction-selective responses in DSGCs in both mice and rabbits (Yoshida et al, 2001;Amthor et al, 2002;Euler et al, 2002;Taylor and Smith, 2012;Hillier et al, 2017) and also exist in the nonhuman primate retina (macaque and marmoset), as well as in the human retina (Hutchins and Hollyfield, 1987;Rodieck, 1989;Rodieck and Marshak, 1992;Moritoh et al, 2013;Zhang et al, 2018). Morphological surveys of RGC type variation in macaques and marmosets have proposed putative primate DSGCs based on their co-stratification with the dendrites of SACs in the inner plexi-form layer; Dacey, 2004;Yamada et al, 2005;Moritoh et al, 2013;Masri et al, 2016).…”

Heterogeneous Presynaptic Distribution of Munc13 Isoforms at Retinal Synapses and Identification of an Unconventional Bipolar Cell Type with Dual Expression of Munc13 Isoforms: A Study Using Munc13-EXFP Knock-in Mice

“…The presence of conventional and ribbon synaptic sites and of Munc13-3 and ubMunc13-2 in terminals of type 6 ON bipolar cells raises the intriguing possibility of a combinatory release of different types of neurotransmitters. To pursue this possibility, we labeled type 6 ON bipolar cells in combination with representative markers for glutamatergic synapses (vesicular glutamate transporters 1, 2, and 3 (VGLUT; [ 38 , 39 , 40 ]), cholinergic synapses (choline acetyltransferase (ChAT; [ 41 , 42 ]), and GABA-/glycinergic synapses (VGAT [ 43 , 44 ] and GLYT1 [ 45 , 46 ]). Syt II-positive terminals of type 6 ON bipolar cells strongly co-localized with VGLUT1 staining ( Figure 7 A).…”