The omega-3 fatty acid docosahexaenoic acid (DHA) inversely relates to neurological impairments with aging; however, limited nondietary models manipulating brain DHA have hindered a direct linkage. We discovered that loss of long-chain acyl-CoA synthetase 6 in mice ( Acsl6 ^–/– ) depletes brain membrane phospholipid DHA levels, independent of diet. Here, Acsl6 ^–/– brains contained lower DHA compared with controls across the life span. The loss of DHA- and increased arachidonate-enriched phospholipids were visualized by MALDI imaging predominantly in neuron-rich regions where single-molecule RNA in situ hybridization localized Acsl6 to neurons. ACSL6 is also astrocytic; however, we found that astrocyte-specific ACSL6 depletion did not alter membrane DHA because astrocytes express a non–DHA-preferring ACSL6 variant. Across the life span, Acsl6 ^–/– mice exhibited hyperlocomotion, impairments in working spatial memory, and increased cholesterol biosynthesis genes. Aging caused Acsl6 ^–/– brains to decrease the expression of membrane, bioenergetic, ribosomal, and synaptic genes and increase the expression of immune response genes. With age, the Acsl6 ^–/– cerebellum became inflamed and gliotic. Together, our findings suggest that ACSL6 promotes membrane DHA enrichment in neurons, but not in astrocytes, and is important for neuronal DHA levels across the life span. The loss of ACSL6 impacts motor function, memory, and age-related neuroinflammation, reflecting the importance of neuronal ACSL6-mediated lipid metabolism across the life span.

The hyaluronan-based extracellular matrix is expressed throughout nervous system development and is well-known for the formation of perineuronal nets around inhibitory interneurons. Since perineuronal nets form postnatally, the role of hyaluronan in the initial formation of neural circuits remains unclear. Neural circuits emerge from the coordinated electrochemical signaling of excitatory and inhibitory synapses. Hyaluronan localizes to the synaptic cleft of developing excitatory synapses in both human cortical spheroids and the neonatal mouse brain and is diminished in the adult mouse brain. Given this developmental-specific synaptic localization, we sought to determine the mechanisms that regulate hyaluronan synthesis and signaling during synapse formation. We demonstrate that hyaluronan synthase-2, HAS2, is sufficient to increase hyaluronan levels in developing neural circuits of human cortical spheroids. This increased hyaluronan production reduces excitatory synaptogenesis, promotes inhibitory synaptogenesis, and suppresses action potential formation. The hyaluronan receptor, CD44, promotes hyaluronan retention and suppresses excitatory synaptogenesis through regulation of RhoGTPase signaling. Our results reveal mechanisms of hyaluronan synthesis, retention, and signaling in developing neural circuits, shedding light on how disease-associated hyaluronan alterations can contribute to synaptic defects.

The thalamus integrates sensory, motor, and associative functions via distinct nuclei, yet the developmental principles driving their specification remains unclear. Here, we generate a spatiotemporal single-cell multiomic and spatial transcriptomic atlas of the embryonic mouse thalamus, combined with barcoding-based lineage tracing. We identify two major glutamatergic lineages—sensory and motor/associative—each governed by different gene regulatory programs and temporal dynamics. These lineages arise from spatially and molecularly isolated progenitors, revealing an early segregation of functional identities. Within the sensory lineage, we resolve two discrete trajectories leading to first-order visual and somatosensory neurons, both emerging from a shared higher-order default state. Using in silico predictions and in vivo perturbations, we identify Sp9 as a key regulator of visual thalamic fate. Together, our findings define the molecular architecture and developmental trajectories that underpin thalamic modality specification, providing a framework to understand how functional circuits emerge in the mammalian brain.

Neural activity is a fundamental driver of early circuit assembly, yet how it shapes the distribution of inhibitory neurons across sensory networks remains poorly understood. Establishing an appropriate balance between excitation and inhibition is essential for effective sensory processing, but the contribution of activity-dependent mechanisms to interneuron allocation across subcortical and cortical stations is unclear. Here, we use region-specific transgenic mouse models of either sex to selectively manipulate activity at distinct loci and developmental stages of the visual pathway. We show that intrinsic thalamic activity is a key regulator of interneuron density in the dorsolateral geniculate nucleus during early postnatal development. Disruption of thalamic activity leads to persistent increases in interneuron proportion, independent of retinal axon targeting. Moreover, altered thalamic activity propagates to the cortex, producing layer-specific changes in parvalbumin- and somatostatin-expressing interneuron populations in primary visual cortex. Together, our findings identify intrinsic thalamic activity as a central organizer of inhibitory circuit assembly across the visual system, coordinating interneuron integration in both thalamus and cortex during critical developmental windows.

The thalamus integrates sensory, motor and associative functions through distinct nuclei, yet the developmental principles driving their specification remain unclear. Here we generate a spatiotemporal single-cell multiomic and spatial transcriptomic atlas of the embryonic mouse thalamus, combined with barcoding-based lineage tracing. We identify two major glutamatergic lineages, sensory-related and motor-associative, each governed by different gene regulatory programs and temporal dynamics. These lineages arise from spatially and molecularly distinct progenitor domains, revealing an early segregation of functional identities. Within the sensory lineage, we resolve branching sensory trajectories leading to first-order visual and somatosensory neurons, both emerging from a shared higher-order-like state. Using in silico predictions and in vivo perturbation, we identify Sp9 as a key regulator of visual thalamic fate. Together, our findings define the molecular architecture and developmental trajectories that underpin thalamic modality specification, providing a framework to understand how functional circuits emerge in the mammalian brain.