Alzheimer's disease (AD) is a progressive neurodegenerative disorder traditionally defined by the accumulation of amyloid‑β plaques and neurofibrillary tangles. Increasing evidence suggests that white‑matter degeneration and myelin disruption occur early in disease progression and may contribute to neuropathological vulnerability. Here, we performed ultrastructural analyses in the 3xTg and 5xFAD mouse models of AD across developmental stages (3-12 months of age), including ages preceding overt amyloid plaque formation or neuronal loss. We identify a spectrum of oligodendrocyte‑ and myelin‑associated abnormalities, including single‑membrane herniations, myelin outfolds, and ectopic myelination of neuronal processes, which are evident as early as 3 months of age and are frequently associated with altered neuropil architecture and incipient dystrophic neurite morphology. These malformations were confirmed to be oligodendrocyte‑derived through O4 immunolabeling. Collectively, our findings reveal early, widespread myelin‑associated ultrastructural alterations that form a consistent structural component of neuritic pathology in AD models. We propose that dysregulated oligodendrocyte membrane remodeling represents an early pathological feature of AD, providing a framework for future studies examining how glial pathology intersects with neuronal degeneration and plaque‑associated neuritic remodeling.

The aggregation of the microtubule-associated protein tau into oligomeric complexes is strongly correlated with the onset and progression of neurodegeneration in Alzheimer's disease (AD). Increasing evidence implicates nuclear membrane disruption in AD and related tauopathies; however, whether this is a cause or consequence of neurodegeneration remains unresolved. Here, we show that nuclear lamina disruption emerges at the early Braak stages, coinciding with the initial formation of pathological tau aggregates in post-mortem AD brain tissue. Using the tauopathy mouse model (P301S PS19), we demonstrate that oligomeric tau (oTau) directly binds to the Lamin B Receptor (LBR), inducing nuclear envelope invaginations as revealed by electron microscopy. These structural alterations are accompanied by chromatin remodeling and gene expression dysregulation. To dissect the underlying mechanism, we employed a light-inducible OptoTau system (4R1N Tau::mCherry::Cry2Olig) in human iPSC-derived neurons, enabling real-time visualization of tau aggregation dynamics. This system revealed selective recruitment of oTau to the nuclear envelope and direct interactions with LBR and Lamin B2, leading to nuclear deformation and activation of the protein translational stress response. Together, these findings identify nuclear membrane disruption as an early and potentially causative event in tau-mediated neurodegeneration, establishing a mechanistic link between tau oligomerization, nuclear stress, and chromatin remodeling. Targeting nuclear destabilization may offer new therapeutic avenues for mitigating AD pathogenesis.

Wide-field (WF) neurons of the tectopulvinar pathway integrate retinal and cortical inputs via large dendritic arbors crucial for rapid visual motion detection. Previous studies identified potential marker genes for mouse WF neurons. Here, we validate CBLN2 as a molecular marker of the tree shrew WF neurons and construct AAVs that exploit CBLN2 promoter to selectively target WF neurons across species. Using intersectional genetics in the tree shrew, we show that WF neuron dendrites receive a distinct pattern of VGluT1+ and VGluT2+ inputs based on their distance from the cell body in the dorsoventral axis of the superior colliculus (SC). This represents the first example of a viral tool derived from the tree shrew genome for cell-type-specific targeting across species. Our results provide a foundation for studying SC circuitry in higher-order mammals and for extending this approach to additional conserved cell types in the SC and other brain regions.

The microtubule-associated protein tau aggregates into oligomeric complexes that highly correlate with Alzheimer's disease (AD) progression. Increasing evidence suggests that nuclear membrane disruption occurs in AD and related tauopathies, but whether this is a cause or consequence of neurodegeneration remains unclear. Using the optogenetically inducible 4R1N Tau::mCherry::Cry2Olig (optoTau) system in iPSC-derived neurons, we demonstrate that tau oligomerization triggers nuclear rupture and nuclear membrane invagination. Pathological tau accumulates at sites of invagination, inducing structural abnormalities in the nuclear envelope and piercing into the nuclear space. These findings were confirmed in the humanized P301S tau (PS19) transgenic mouse model, where nuclear envelope disruption appeared as an early-onset event preceding neurodegeneration. Further validation in post-mortem AD brain tissues revealed nuclear lamina disruption correlating with pathological tau emergence in early-stage patients. Notably, electron microscopy shows that tau-induced nuclear invagination triggers global chromatin reorganization, potentially driving aberrant gene expression and protein translation associated with AD. These findings suggest that nuclear membrane disruption is an early and possibly causative event in tau-mediated neurodegeneration, establishing a mechanistic link between tau oligomerization and nuclear stress. Further investigation into nuclear destabilization could inform clinical strategies for mitigating AD pathogenesis.

Mitochondrial dysfunction is increasingly recognized as a key factor in Alzheimer's disease (AD) pathogenesis, but the precise relationship between mitochondrial dynamics and proteinopathies in AD remains unclear. This study investigates the role of mitochondrial dynamics and function in the hippocampal tissue and peripheral blood mononuclear cells (PBMCs) of 5xFAD transgenic mice, as a model of AD. The levels of mitochondrial fusion proteins OPA1 and MFN2 and fission proteins DRP1 and phospho-DRP1 (S616) at 3, 6, and 9 months of age were assessed. Western blot analysis revealed significantly lower levels of OPA1 and MFN2 in the hippocampus of 6- and 9-month-old transgenic (TG) 5xFAD mice compared to controls (CTR), while DRP1 and pDRP1 levels were increased in 9-month-old TG mice. Additionally, MFN2 were decreased in the PBMCs of 9-month-old TG mice, indicating systemic mitochondrial alterations. Ultrastructural analysis of hippocampal tissues showed substantial alterations in mitochondrial morphology, including abnormalities in size and shape, a preponderance of teardrop-shaped mitochondria, and alterations in the somatic mitochondria-ER complex. Notably, mitochondria-associated ER contact sites were more distant in TG mice, suggesting functional impairments. Flow cytometric measurements demonstrated decreased mitochondrial membrane potential and mass, along with increased superoxide production, in the PBMCs of TG mice, particularly at 9 months, highlighting compromised mitochondrial function. Levels of key mitochondrial proteins including VDAC, TOM2O, and mitophagy-related protein PINK1 levels altered in both central and peripheral tissue of TG mice. These findings suggest that mitochondrial dysfunction and altered dynamics are early events in AD development in 5xFAD mice, manifesting in both central and peripheral tissues, and support the notion that mitochondrial abnormalities are an integral component of AD pathology. These insights might lead to the development of targeted therapies that modulate mitochondrial dynamics and function to mitigate AD progression.

In the mammalian visual system, three functionally distinct parallel processing streams extend from the retina to the visual thalamus and then to the visual cortex: magnocellular (M), parvocellular (P), and koniocellular (K). Tree shrews (Tupaia belangeri), a preprimate species, provide an advantageous model to study the K pathway in isolation because, while M and P pathways remain mixed in Lamina 1 (L1), L2, L4, and L5 of the lateral geniculate nucleus (LGN), L3 and L6 receive strictly K-input from the contralateral eye. Additionally, K-input laminae selectively receive glutamatergic axons from the superior colliculus. To reveal how cellular and synaptic properties of K geniculate laminae may differ from M/P laminae and how tectal input may shape the K relay to the cortex, we studied the morphology and connectivity of retinal and tectal terminals in pathway-specific laminae. While confirming that K laminae relay cells contain calbindin, we also found its expression in GABAergic cells across all laminae. No cell-type or lamina specificity was observed for parvalbumin. Ultrastructurally, retinal terminals are morphologically distinct in M/P versus K laminae. Tectogeniculate axons in L3 and L6 resemble retinal terminals in their morphology and synaptic targets, while corticogeniculate terminals are sparse in L6. VGluT2, the molecular marker for large-sized driver terminals, is expressed prominently in one of the three tectal cell types that project to LGN. Morphological differences in synaptic circuitry between L3 and L6 provide further evidence that two geniculate K laminae are differentially innervated to relay distinct sets of information to the cortex.

The superior colliculus (SC), a midbrain sensorimotor hub, is anatomically and functionally similar across vertebrates, but how its cell types have evolved is unclear. Using single-nucleus transcriptomics, we compared the SC's molecular and cellular organization in mice, tree shrews, and humans. Despite over 96 million years of evolutionary divergence, we identified  30 consensus neuronal subtypes, including Cbln2+ neurons that form the SC-pulvinar circuit in mice and tree shrews. Synapse-related genes were among the most conserved in the SC, unlike neocortex, suggesting co-conservation of synaptic genes and collicular circuitry. In contrast, cilia-related genes diverged significantly across species, highlighting the potential importance of the neuronal primary cilium in SC evolution. Additionally, we identified an inhibitory SC neuron in tree shrews and humans but not mice. Our findings reveal that the SC has evolved by conserving neuron subtypes, synaptic genes, and circuitry, while diversifying ciliary gene expression and an inhibitory neuron subtype.

UNLABELLED: Alzheimer's disease (AD) research has been hindered by the lack of models that faithfully recapitulate the full profile of disease progression in a human genetic background. We developed a 3D assembloid model ("Masteroid") using iPSC-derived neurons, astrocytes, and microglia from APOE4/4 and isogenic control lines. Neurons were seeded with tau oligomers, then combined with astrocytes and microglia to form mature 3D Masteroids, followed by amyloid-β oligomer exposure. After four weeks, AD-Masteroids exhibited hallmark pathologies, including extracellular amyloid-β deposits, intracellular tau aggregation, neurodegeneration, astrogliosis, and microglial activation, with APOE4 exacerbating all phenotypes. Single-cell RNA sequencing further identified novel roles of IGFBP pathways in amyloid-β and tau-mediated pathology. This innovative platform provides a robust system to dissect cellular and molecular mechanisms of AD progression and offers a powerful tool for therapeutic discovery.

HIGHLIGHTS: The 3D human neuron-glia assembloid ("Masteroid"), composed of neurons, astrocytes, microglia, and oligodendrocytes, faithfully recapitulates human brain ultrastructure and intercellular interactions.Exposure to oligomeric tau and Aβ induced hallmark Alzheimer's pathologies, including amyloid deposition, tau aggregation, neurodegeneration, and gliosis.The APOE4 genotype exacerbated all pathological features, highlighting its role in driving multicellular interactions that accelerate disease progression.The IGF signaling axis was identified as a key mediator of Aβ- and tau-induced pathology and a potential therapeutic target.