Biology subjects

Ackerman, S. D.

Publications and source records attributed to Ackerman, S. D..

6 recordsLinked to original sources

bioRxiv2026

A CRISPR/Cas9 screen reveals convergent dysregulation of neurological pathways within and across glycosylation pathways

Congenital disorders of glycosylation (CDG) are a broad group of disorders characterized by deficient glycosylation. CDG are caused by mutations in over 160 different genes regulating distinct steps and types of glycosylation. Despite the diversity of CDG-causing genes, patient phenotypes often overlap, with neurological symptoms present across many CDG. However, models to study conserved mechanisms underlying neurological dysfunction across CDG types are lacking. Therefore, we leveraged CRISPR/Cas9 to knockdown 15 glycosylation genes in zebrafish spanning 7 CDG classes. Through behavioral assays and in vivo imaging, we report changes in mobility, response to stimuli, and neuronal activity in many of our models. To uncover the molecular underpinnings of these phenotypes, we performed bulk-RNA sequencing on our models. We report differential expression in genes related to neurological development and function across all tested CDG classes, which will inform future hypothesis-driven studies defining new molecular targets for therapeutic intervention in CDG.

neuroscience↗

bioRxiv2022

A Drosophila glial cell atlas reveals that transcriptionally defined cell types can be morphologically diverse

Morphology is a defining feature of neuronal identity. Like neurons, glia display diverse morphologies, both across and within glial classes, but are also known to be morphologically plastic. Here, we explored the relationship between glial morphology and transcriptional signature using the Drosophila central nervous system, where glia are categorized into five main classes (outer and inner surface glia, cortex glia, ensheathing glia, and astrocytes), which show within-class morphological diversity. We analysed and validated single cell RNA sequencing data of Drosophila glia in two well-characterized tissues from distinct developmental stages, containing distinct circuit types: the embryonic ventral nerve cord (motor) and the adult optic lobes (sensory). Our analysis identified a new morphologically and transcriptionally distinct surface glial population in the ventral nerve cord. However, many glial morphological categories could not be distinguished transcriptionally, and indeed, embryonic and adult astrocytes were transcriptionally analogous despite differences in developmental stage and circuit type. While we did detect extensive within-class transcriptomic diversity for optic lobe glia, this could be explained entirely by glial residence in the most superficial neuropil (lamina) and an associated enrichment for immune-related gene expression. In summary, we generated a single-cell transcriptomic atlas of glia in Drosophila, and our extensive in vivo validation revealed that glia exhibit more diversity at the morphological level than was detectable at the transcriptional level. This atlas will serve as a resource for the community to probe glial diversity and function.

neuroscience↗

bioRxiv2021

Synapse-associated astrocyte mitochondria stabilize motor circuits to prevent excitotoxicity

Neurons have an outsized metabolic demand, requiring continuous metabolic support from non-neuronal cells called glia. When this support fails, toxic metabolic byproducts accumulate, ultimately leading to excitotoxicity and neurodegeneration. Astrocytes, the primary synapse-associated glial cell type, are known to provide essential metabolites (e.g. lactate) to sustain neuronal function. Here, we leverage the well-characterized Drosophila motor circuit to investigate another means of astrocyte-to-neuron metabolic support: activity-dependent trafficking of astrocyte mitochondria. Following optogenetic activation, motor neuron mitochondria migrate away from synapses. By contrast, astrocytic mitochondria accumulated peri-synaptically, and at times, were transferred into neighboring neurons. A genetic screen identified the mitochondrial adaptor protein Milton as a key regulator of this process. Astrocyte-specific milton knockdown disrupted regular mitochondrial trafficking, resulting in locomotor deficits, dysfunctional motor activity, and altered synapse number at the neuromuscular junction. These findings suggest that astrocytes dynamically redistribute mitochondria to buffer metabolic demand at synapses, highlighting a potential mechanism by which glia protect neural circuits from metabolic failure and neurodegeneration.

neuroscience↗

bioRxiv2020

Postembryonic screen for mutations affecting spine development in zebrafish

The spinal vertebral column gives structural support for the adult body plan, protects the spinal cord, and provides muscle attachment and stability, which allows the animal to move within its environment. The development and maturation of the spine and its physiology involve the integration of multiple musculoskeletal tissues including bone, cartilage, and fibrocartilaginous joints, as well as innervation and control by the nervous system. One of the most common disorders of the spine in human is adolescent idiopathic scoliosis (AIS), which is characterized by the onset of an abnormal lateral curvature of the spine of <10{degrees} around adolescence, in otherwise healthy children. The genetic basis of AIS is largely unknown. Systematic genome-wide mutagenesis screens for embryonic phenotypes in zebrafish have been instrumental in the understanding of early patterning of embryonic tissues necessary to build and pattern the embryonic spine. However, the mechanisms required for postembryonic maturation and homeostasis of the spine remain poorly understood. Here we report the results from a small-scale forward genetic screen for adult-viable recessive and dominant mutant zebrafish, displaying overt morphological abnormalities of the adult spine. Germline mutations induced with N-ethyl N-nitrosourea (ENU) were transmitted and screened for dominant phenotypes in 1,229 F1 animals, and subsequently bred to homozygosity in F3 families, from these, 314 haploid genomes were screened for recessive phenotypes. We cumulatively found 39 adult-viable (3 dominant and 36 recessive) mutations each leading to a defect in the morphogenesis of the spine. The largest phenotypic group displayed larval onset axial curvatures, leading to whole-body scoliosis without vertebral dysplasia in adult fish. Pairwise complementation testing within this phenotypic group revealed at least 16 independent mutant loci. Using massively-parallel whole genome or whole exome sequencing and meiotic mapping we defined the molecular identity of several loci for larval onset whole-body scoliosis in zebrafish. We identified a new mutation in the skolios/kinesin family member 6 (kif6) gene, causing neurodevelopmental and ependymal cilia defects in mouse and zebrafish. We also report several recessive alleles of the scospondin and a disintegrin and metalloproteinase with thrombospondin motifs 9 (adamts9) genes, which all display defects in spine morphogenesis. Many of the alleles characterized thus far are non-synonymous mutations in known essential scospondin and adamts9 genes. Our results provide evidence of monogenic traits that are critical for normal spine development in zebrafish, that may help to establish new candidate risk loci for spine disorders in humans.

developmental biology↗

bioRxiv2020

Astrocytes close a critical period of motor circuit plasticity

Critical periods - brief intervals where neural circuits can be modified by sensory input - are necessary for proper neural circuit assembly. Extended critical periods are associated with neurodevelopmental disorders, including schizophrenia and autism; however, the mechanisms that ensure timely critical period closure remain unknown. Here, we define the extent of a critical period in the developing Drosophila motor circuit, and identify astrocytes as essential for proper critical period termination. During the critical period, decreased activity produces larger motor dendrites with fewer inhibitory inputs; conversely, increased motor neuron activity produces smaller motor dendrites with fewer excitatory inputs. Importantly, activity has little effect on dendrite morphology after critical period closure. Astrocytes invade the neuropil just prior to critical period closure, and astrocyte ablation prolongs the critical period. Finally, we use a genetic screen to identify astrocyte-motor neuron signaling pathways that close the critical period, including Neuroligin-Neurexin signaling. Reduced signaling destabilizes dendritic microtubules, increases dendrite dynamicity, and impairs locomotor behavior, underscoring the importance of critical period closure. Previous work defines astroglia as regulators of plasticity at individual synapses; here, we show that astrocytes also regulate large-scale structural plasticity to motor dendrite, and thus, circuit architecture to ensure proper locomotor behavior.

neuroscience↗

bioRxiv2018

Fbxw7 is a critical regulator of Schwann cell myelinating potential

Myelin insulates and protects axons in vertebrate nervous systems. In the central nervous system (CNS), oligodendrocytes (OLs) make numerous myelin sheaths on multiple axons, whereas in the peripheral nervous system (PNS) myelinating Schwann cells (SCs) make just one myelin sheath on a single axon. Why the myelinating potentials of OLs and SCs are so fundamentally different is unclear. Here, we find that loss of Fbxw7, an E3 ubiquitin ligase component, enhances the myelinating potential of SCs. Fbxw7 mutant SCs are seen myelinating multiple axons in a fashion reminiscent of OLs as well as aberrantly myelinating large axons while simultaneously ensheathing small unmyelinated axons - typically distinct roles of myelinating SCs and non-myelinating Remak SCs, respectively. We found that several of the Fbxw7 mutant phenotypes, including the ability to generate thicker myelin sheaths, were due to dysregulation of mTOR. However, the remarkable ability of mutant SCs to either myelinate multiple axons or myelinate some axons while simultaneously encompassing other unmyelinated axons is independent of mTOR signaling. This indicates distinct roles for Fbxw7 in regulating multiple aspects of SC behavior and that novel Fbxw7-regulated mechanisms control modes of myelination previously thought to fundamentally distinguish myelinating SCs from non-myelinating SCs and OLs. Our data reveal unexpected plasticity in the myelinating potential of SCs, which may have important implications for our understanding of both PNS and CNS myelination and myelin repair.

neuroscience↗