Abstract
Astrocytes regulate the formation and function of neuronal synapses via multiple signals; however, what controls regional and temporal expression of these signals during development is unknown. We determined the expression profile of astrocyte synapse-regulating genes in the developing mouse visual cortex, identifying astrocyte signals that show differential temporal and layer-enriched expression. These patterns are not intrinsic to astrocytes, but regulated by visually evoked neuronal activity, as they are absent in mice lacking glutamate release from thalamocortical terminals. Consequently, synapses remain immature. Expression of synapse-regulating genes and synaptic development is also altered when astrocyte signaling is blunted by diminishing calcium release from astrocyte stores. Single-nucleus RNA sequencing identified groups of astrocytic genes regulated by neuronal and astrocyte activity, and a cassette of genes that show layer-specific enrichment. Thus, the development of cortical circuits requires coordinated signaling between astrocytes and neurons, highlighting astrocytes as a target to manipulate in neurodevelopmental disorders.
Highlights
Synapses are points of contact where electro-chemical signals are transferred between neurons in a given circuit (Petzoldt and Sigrist, 2014; SĆ¼dhof, 2018)
differentially expressed genes (DEGs) are classified into total genes, genes that are expressed by astrocytes (IP/input >0.75), and genes that are enriched in astrocytes (IP/input >3; Figure 1D, for definitions see (Boisvert et al, 2018))
For genes that encode proteins important for astrocyte function, we found that the metabotropic glutamate receptor Grm5 is most highly expressed at P7 and declines with maturation, confirming previous reports (Catania et al, 1994; Sun et al, 2013), while the glutamate transporter Slc1a2 (Glt1) and the connexins (Gja1, Gjb6) are significantly upregulated from P14 onwards (Figure 1I). 167 Astrocytic synapse-regulating genes show differential spatio-temporal expression 168 patterns
Summary
Synapses are points of contact where electro-chemical signals are transferred between neurons in a given circuit (Petzoldt and Sigrist, 2014; SĆ¼dhof, 2018). Glypicans induce the formation of active synapses by recruiting GLUA1 to the postsynaptic side (Allen et al., 2012; Farhy-Tselnicker et al, 2017) and chordin-like 1 induces synapse maturation by recruiting GLUA2 to the postsynaptic side (Blanco-Suarez et al, 2018) These and other signals have been identified using in vitro cell culture approaches and analyzed individually across ages and brain regions in vivo. Single-nucleus RNA sequencing analysis reveals diverse populations of astrocytes in the developing VC, and identifies novel groups of genes that are regulated by neuronal and astrocyte activity These findings demonstrate how astrocyte expression of synapse-regulating genes is controlled during development, and how synapse maturation is dependent on neuron astrocyte communication. These data further provide an important resource for future studies of 85 astrocyte development and astrocyte regulation of synapse formation
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