Biology subjects

Baldwin, K. T.

Publications and source records attributed to Baldwin, K. T..

5 recordsLinked to original sources

bioRxiv2026

Morphological Hallmarks of White Matter Astrocytes Across Development

While the mechanisms underlying protoplasmic, or gray matter (GM), astrocyte morphogenesis have been extensively studied, far less is known about the development of fibrous, or white matter (WM), astrocytes. In particular, no study has comprehensively characterized the morphological development of WM astrocytes. To address this gap, we used an intracortical adeno-associated virus injection technique to sparsely label individual astrocytes in the mouse corpus callosum for morphological analysis across postnatal development. We found that astrocytes in the corpus callosum follow a distinct trajectory of morphological development from their GM cousins. They establish their branching complexity in the first two postnatal weeks and significantly increase in volume into adulthood. We further show that tiling is conserved in WM astrocytes and that a subset of mature astrocytes in the corpus callosum lack endfeet. These findings provide the first developmental framework for the morphogenesis of callosal astrocytes and establish a foundation for future studies investigating the molecular mechanisms regulating the development of WM astrocytes.

neuroscience↗

bioRxiv2026

Altered astrocyte morphology in pathogenic HEPACAM variants: a multipoint analysis and new machine learning framework for 3D Sholl analysis

Astrocytes are morphologically complex glial cells that play critical roles in brain development and function. Altered astrocyte morphology is associated with altered astrocyte function and is a common feature of many neurological disorders. Astrocytes express numerous membrane proteins that are important for their morphogenesis, including hepaCAM, an astrocyte-enriched cell adhesion molecule that regulates astrocyte branching organization, tiling, and coupling. Pathogenic variants of HEPACAM that impair homophilic protein interaction cause megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare and early-onset leukodystrophy characterized by white matter edema, seizures, and cognitive and motor decline. Pathogenic variants show altered subcellular localization and impaired interaction with key binding partners, but the impact on astrocyte morphology remains unexplored. Here we expressed three different dominant pathogenic HEPACAM variants in astrocytes of the developing mouse cortex and performed a comprehensive multipoint analysis of astrocyte morphology. Using established analysis workflows and a new machine learning model for efficient 3D Sholl analysis, we found small, but significant increases in morphological complexity for the G89S pathogenic variant, which impairs homophilic cis interaction of hepaCAM, and the Q56P pathogenic variant, which impairs homophilic trans interaction. This phenotype is distinct from the morphological changes we previously observed in Hepacam knockout astrocytes, suggesting that dominant variants may impact astrocyte morphology through a gain-of-function, rather than a loss-of-function, mechanism. Our study also provides a new machine learning workflow for streamlined 3D analysis of astrocyte branching complexity along with a framework for performing multivariate analysis of astrocyte morphology metrics across multiple conditions.

neuroscience↗

bioRxiv2025

Dominant MLC-causing mutations alter hepaCAM subcellular localization and protein interactome in astrocytes of the developing mouse cortex

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare leukodystrophy characterized by early-onset macrocephaly, white matter edema, seizures, and motor and cognitive decline. Missense mutations to hepatic and glial cell adhesion molecule (hepaCAM), also known as GlialCAM, are responsible for approximately twenty-five percent of MLC cases. HepaCAM is highly enriched in astrocytes and plays important roles in astrocyte territory establishment, gap junction coupling, branching organization, synaptic function, and development of the gliovascular unit. The molecular mechanisms through which MLC-causing missense mutations alter hepaCAM function in vivo and facilitate MLC pathogenesis during brain development remain largely unknown. Here, we used new viral tools and proximity-based proteomics to examine how three different dominant MLC-causing mutations impact hepaCAM subcellular localization and protein interactome in astrocytes of the developing mouse cortex. We found dramatic defects in hepaCAM distribution throughout the astrocyte, which were common to all mutants tested. We also observed significant changes in protein interactome between wild type and mutant hepaCAM, including decreased association with previously described hepaCAM-interacting proteins Connexin 43 and CLC-2. Moreover, we identified changes in association between hepaCAM and a number of previously undescribed potential hepaCAM-interaction partners, including the epilepsy-associated potassium channel KCNQ2. Collectively, our data provide new insights into hepaCAM function in astrocytes during brain development, reveal altered hepaCAM protein dynamics with MLC missense mutations, and provide a new resource to explore the molecular underpinnings of MLC pathogenesis.

neuroscience↗

bioRxiv2025

Astrocyte-derived PTPRZ1 regulates astrocyte morphology and excitatory synaptogenesis

Protein tyrosine phosphatase receptor type Z1 (PTPRZ1) is one of the most abundantly expressed and enriched proteins in astrocytes during development, yet its function in astrocytes is unknown. Using an astrocyte-neuron co-culture system, we found that knockdown of Ptprz1 in astrocytes significantly impaired astrocyte branching morphogenesis. To investigate the function of PTPRZ1 in astrocytes during brain development, we generated a Ptprz1 conditional knockout mouse and deleted Ptprz1 from astrocytes postnatally, after the bulk of astrogenesis is complete. At postnatal day 21, we found defects in astrocyte morphology and a reduction in excitatory synapse number across multiple layers of the visual cortex, suggesting important functions for astrocytic PTPRZ1 in both astrocyte morphogenesis and synaptogenesis. PTPRZ1 is expressed in several neural cell types, including radial glial stem cells and oligodendrocyte progenitor cells (OPCs), and regulates critical aspects of neurodevelopment, including neurite outgrowth, neuronal differentiation, myelination, and extracellular matrix (ECM) development. Moreover, altered PTPRZ1 expression is associated with schizophrenia and glioblastoma. Therefore, this mouse model is a valuable resource for investigating cell-type-specific PTPRZ1 function in numerous neurodevelopmental and neuropathological mechanisms.

neuroscience↗

bioRxiv2020

Small-hairpin RNAs cause target-independent microRNA dysregulation in neurons and elicit global transcriptomic changes

Small hairpin RNAs (shRNAs) allow highly efficient gene knockdown. Here we employed different shRNAs to knock down the reticulon RTN4A/NogoA in primary neurons. Depletion of NogoA correlates with altered synaptic protein composition and spontaneous neurotransmission. However, similar phenotypes are not observed upon genetic deletion of Nogo or its receptors. Step-wise introduction of mismatches in the seed region of shNogoA provides further evidence that synaptic phenotypes are NogoA-independent. RNA sequencing revealed global changes in the neuronal transcriptome of cultures transduced with the original shNogoA or closely related variants. Transcriptomic changes are shRNA seed sequence dependent, but not target-specific. Parallel sequencing of small non-coding RNAs revealed dysregulation of microRNAs. Computational analysis shows that the altered miRNA composition correlates with changes in mRNA expression and preferentially affects protein-protein networks that function at synapses. Thus, off-target effects associated with shRNAs are an inherent property, and in particular, altered miRNA composition needs careful consideration.

neuroscience↗