A Distinct Layer 1 Astrocyte Program Shapes Perisynaptic Structure and Calcium Signaling in Mouse Motor Cortex

Although layer-specific molecular and morphological diversity among cortical astrocytes is increasingly well established, how these distinct states are linked to specialized calcium signaling and maintained in the adult cortex remains unclear. Here, combining super-resolution structural imaging, two-photon calcium imaging, and analysis of public single-cell and spatial transcriptomic resources, we identify Layer 1 (L1) astrocytes in mouse primary motor cortex as a distinct superficial astrocyte program. These cells occupy compact territories yet contain dense synapse-associated loop-like structures and display frequent, fast, broadly spreading calcium events that engage a large fraction of the territory. Transcriptomic analyses identify Id1 and Id3 as enriched components of this superficial program. CRISPR-Cas9 deletion of Id1 and Id3 in adult astrocytes selectively disrupts L1 and superficial Layer 2/3 (L2/3) astrocytes, expanding territory size, reducing fine-process complexity, and suppressing calcium activity. Thus, adult layer-specific transcriptional programs maintain specialized astrocyte structure and signaling. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=185 SRC="FIGDIR/small/712002v1_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@89c916org.highwire.dtl.DTLVardef@1f0d71eorg.highwire.dtl.DTLVardef@bb02f3org.highwire.dtl.DTLVardef@1bedf7e_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LILayer 1 astrocytes in mouse motor cortex have compact, loop-rich nanoarchitecture C_LIO_LILayer 1 astrocytes show fast, frequent, widespread calcium events C_LIO_LISingle-cell data define a superficial astrocyte state enriched for Id1 and Id3 C_LIO_LIAdult Id1/Id3 loss selectively disrupts Layer 1 astrocyte structure and calcium C_LI In BriefBhattacharjee et al., identify a specialized Layer 1 astrocyte state in mouse motor cortex, defined by compact, loop-rich nanoarchitecture and unusually high calcium signaling. Id1/Id3 deletion selectively disrupts this superficial program, linking layer-specific astrocyte form and function to adult transcriptional control.