TABLE 5.

Examples of astrocyte heterogeneity and diversity

Heterogeneity/diversity metric	Example references
Location and morphology
CNS region (brain, spinal cord, retina; e.g., Bergmann glia, Müller glia) Tissue region (e.g., neocortex vs. cerebellar cortex, cervical vs. lumbar spinal cord) Gray versus white matter (protoplasmic vs. fibrous astrocytes) Layer/lamina (e.g., Bergmann glia vs. velate astrocytes in the cerebellar cortex)	Chai et al., 2017; Köhler et al., 2021; Lanjakornsiripan et al., 2018; Matyash & Kettenmann, 2010; Reichenbach & Wolburg, 2012; Somjen, 1988
Gene expression profilea
Brain: At least six groups Cortex: Layer-specific; at least five subtypes Hippocampus: At least five subtypes Striatum: Continuous transcriptional gradient	Batiuk et al., 2020; Chai et al., 2017; Doyle et al., 2008; Gokce et al., 2016; John Lin et al., 2017; Lanjakornsiripan et al., 2018; Morel et al., 2017; Zeisel et al., 2015
Biochemical and physiological properties
Transporter expression (e.g., GLAST) Ion channel expression (e.g., Kir4.1) Gap junctional coupling (e.g., Cx43) Ca2+ signaling (e.g., hippocampus vs. striatum) Metabolism Structural properties (e.g., GFAP expression, spine coverage)	Chai et al., 2017; Fernández-Moncada et al., 2021; Herde et al., 2020; Hirrlinger et al., 2008; Kelley et al., 2018; Köhler et al., 2021; Köhler et al., 2018; Kronschläger et al., 2021; Miller et al., 2019; Oheim et al., 2018; Olsen et al., 2007; Theis & Giaume, 2012
Species
Worms, flies, and fish (e.g., injury-responsive CNS glia) Mammals (e.g., reactive astrocytes) Humans (e.g., interlaminar astrocytes)	Freeman & Rowitch, 2013; Nagai, Yu, et al., 2021

^aSee Hirbec et al., 2020 for a recent overview on scRNAseq studies on glial cells.