Becalick, A. | Search bioRxiv

bioRxiv2026

The adaptor protein DAB2 cell-autonomously links APOE with disease-associated microglia (DAM)/TREM2 state dysregulation associated with Alzheimer's disease

The neuron-secreted Reelin (RELN) protein and its adaptor DAB1 modify Alzheimer's disease (AD) risk through genetic interaction with APOE4. While RELN and APOE4 exert antagonistic effects on amyloid and Tau pathology in mice, how risk is conferred in the human brain remains unclear. The related adaptor DAB2 endocytoses RELN/APOE receptors and, via LRP8, modulates non-canonical pro-inflammatory signalling in non-neuronal cells. We hypothesised that RELN and APOE signalling directly influence microglial function to modify AD risk. Integrating human brain transcriptomics, a Reln-deficient mouse, and DAB1/DAB2 knock-down in APOE isogenic iPSC-microglia, we found that microglial DAB1/DAB2 pathways were dynamically regulated across the lifespan, with DAB2 dysregulated with increasing amyloid pathology. DAB2 transcriptional networks correlated with disease- and lipid- associated microglial states (DAM/LDAM) linked to networks expressing dementia-risk loci (TREM2, GRN, ACE, SORL1) and associated with endolysosomal and lipid-handling pathways. DAB2- knockdown cell-autonomously shifted microglia away from gene networks enriched in DAM/TREM2 states and towards pro-inflammatory cytokine-responsive states and TNFNF{kappa}B pathways. APOE4/E4 microglia showed elevated APOE and reduced DAB1pY232 under inflammatory stress, and blunted DAB2-knockdown transcriptomic responses, consistent with pathway-level genetic interaction. In vivo, RELN-deficiency reduced microglial ramification and increased CD68. These findings identify DAB2 as a regulator of microglial state transitions and a modifier of dementia-risk networks linking APOE genotype to inflammatory, phagocytic and amyloid-beta clearance pathways relevant to AD.

neuroscience↗

bioRxiv2025

Barcoded Rabies In Situ Connectomics for high-throughput reconstruction of neural circuits

Sequencing of oligonucleotide barcodes holds promise as a high-throughput approach for reconstructing synaptic connectivity at scale (1). Rabies viruses can act as a vehicle for barcode transmission, thanks to their ability to spread between synaptically connected cells (2, 3). However, applying barcoded rabies viruses to map synaptic connections in vivo has proved challenging (4-7). Here, we develop Barcoded Rabies In Situ Connectomics (BRISC) for high-throughput connectivity mapping in the mouse brain. To ensure that the majority of post-synaptic "starter" neurons are uniquely labeled with distinct barcode sequences, we first generated libraries of rabies viruses with sufficient diversity to label >1000 neurons uniquely. To minimize the probability of barcode transmission between starter neurons, we developed a strategy to tightly control their density. We then applied BRISC to map inputs of single neurons in the primary visual cortex (V1). Using in situ sequencing, we read out the expression of viral barcodes in rabies-infected neurons, while preserving spatial information. We then matched barcode sequences between starter and presynaptic neurons, mapping the inputs of 385 neurons and identifying 7,814 putative synaptic connections. The resulting connectivity matrix revealed layer- and cell-type-specific local connectivity rules and topographic organization of long-range inputs to V1. These results show that BRISC can simultaneously resolve the synaptic connectivity of hundreds of neurons while preserving spatial information, enabling reconstruction of neural circuits at an unprecedented scale.

neuroscience↗