{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Calbindin (CALB1) is a highly conserved calcium‐binding protein that serves both as a functional modulator of intracellular calcium dynamics and as a robust marker of neuronal maturity and subtype identity. In several studies, its expression has been shown to follow a tightly regulated temporal and spatial pattern during brain development. For example, during adult hippocampal neurogenesis calbindin is absent from early postmitotic neurons but becomes expressed as granule cells mature, thereby delineating the transition from an immature to a fully differentiated state."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In the cerebellum, calbindin expression in Purkinje cells is a well‐established marker of cell integrity. Even in pathological conditions where other proteins (such as PKCγ and ataxin 1) are reduced, maintenance of calbindin immunoreactivity indicates that these cells retain key aspects of their phenotype, suggesting a neuroprotective role that may include buffering intracellular calcium to prevent excitotoxicity."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Calbindin’s role extends to neurodegenerative contexts as well. In mouse models of Alzheimer’s disease, reduced levels of calbindin in the dentate gyrus correlate with enhanced inflammatory cytokine expression and cognitive deficits, implying that calbindin‐positive neurons may possess greater resilience to amyloid‐induced toxicity."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " Conversely, in the substantia nigra, calbindin‐expressing dopaminergic neurons appear relatively spared in the face of BDNF depletion, a finding that hints at a protective role for CALB1 in modulating neuronal vulnerability."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In sensory systems, calbindin is used to demarcate distinct interneuron subtypes. In the olfactory bulb, for instance, calbindin-positive periglomerular cells represent one of several GABAergic subtypes with unique maturational and turnover profiles"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": ", and in the retina, calbindin marks specific neuronal populations contributing to the precise stratification of inner plexiform layer circuitry."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Beyond the nervous system proper, calbindin also plays a role in calcium homeostasis in peripheral tissues. In epithelia lining the small intestine and kidney, calbindin co-localizes with channels and transporters involved in calcium absorption, suggesting a functional contribution to epithelial calcium handling."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Furthermore, studies addressing oxidative stress in the brain reveal that while certain inhibitory interneuron subclasses—such as those expressing parvalbumin—are especially susceptible to redox imbalance, calbindin-positive interneurons appear more resistant, implying that CALB1 expression may confer a degree of protection under conditions of cellular stress."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Finally, within the inner ear, calbindin serves as an important marker to distinguish specific sensory hair cell subtypes, thereby contributing to our understanding of hair cell differentiation and the challenges of in vivo sensory cell regeneration."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, these studies underscore that CALB1 is not only a critical calcium-buffering protein but also a versatile marker of cellular differentiation and integrity. Its differential expression across neuronal subtypes and peripheral calcium-handling epithelia underscores its multifaceted role in modulating cellular resilience, maturation, and function in both health and disease."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}, {"type": "fg_f", "ref": "4"}, {"type": "fg_f", "ref": "6"}, {"type": "fg_f", "ref": "5"}, {"type": "fg_f", "ref": "7"}, {"type": "fg_f", "ref": "12"}, {"type": "fg_f", "ref": "9"}, {"type": "fg_f", "ref": "3"}, {"type": "fg_f", "ref": "10"}, {"type": "fg_f", "ref": "8"}, {"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Moritz D Brandt, Sebastian Jessberger, Barbara Steiner, et al. 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