Biology subjects

Zhao, X.-F.

Publications and source records attributed to Zhao, X.-F..

7 recordsLinked to original sources

bioRxiv2025

Neurons maintain sequential order during radial migration by DSCAM-facilitated antagonism of N-Cadherin

Proper radial migration of developing cortical neurons is critical for the "inside-out" laminar organization of the mammalian cerebral cortex. While substantial progress has been made in our understanding of how neurons terminate migration at the cortical plate (CP)/marginal layer (ML) boundary, the mechanisms that control the sequential order of migrating neurons remain poorly understood. Here, we show that radial migration of upper-layer pyramidal neurons is transiently restrained within the upper cortical plate (UCP), where migrating neurons assemble into vertically organized radial queues that maintain inter-neuronal spacing and migratory order. Using time-lapse imaging of embryonic mouse cortex, we found that leading neurons transiently delay nucleokinesis of trailing neurons, thereby synchronizing neuronal movement within the UCP. Loss of Down syndrome cell adhesion molecule (DSCAM) disrupts this coordinated migratory behavior, allowing trailing neurons to bypass preceding neurons, resulting in abnormal neuronal accumulation near the CP/ML boundary. Mechanistically, DSCAM localizes to membrane interfaces between adjacent migrating neurons. At these sites, DSCAM suppresses N-cadherin-mediated intercellular adhesion, limits F-actin assembly, and inhibits expansion of the proximal cytoplasmic dilation required for nucleokinesis. Dscam-deficient neurons exhibit increased cadherin puncta, more neuron-neuron contacts, and accelerated migration through the UCP. Rescue experiments demonstrate that expressing the extracellular domain of Dscam is sufficient to restore ordered migration, suggesting that an extracellular mechanism regulates orderly neuronal migration. In addition, we identify UNC5c-mediated signaling as a counterbalancing force that promotes upward migration within the UCP. Together, our findings identify radial neuronal queues as a previously unrecognized intermediate structure in cortical morphogenesis and establish DSCAM-dependent regulation of inter-neuronal spacing as a mechanism that preserves the migratory order during inside-out corticogenesis.

developmental biology↗

bioRxiv2024

Diverse and Location-Specific Roles of PlexinA2, PlexinA4, and NCAM in Developing Hippocampal Mossy Fibers

Mossy fibers (MFs) originate from dentate granule cells and innervate area CA3 of the hippocampus. Upon entry of CA3, MFs partition into two prominent axon bundles, the suprapyramidal tract (SPT) and infrapyramidal tract (IPT) and form lamina specific synaptic contacts in the stratum lucidum (SL) and stratum oriens (SO), respectively. Here we employed new mouse lines to dissect the function of Sema6A and its receptors, PlexinA2 (PlxnA2) and PlxnA4, in developing MFs. In Sema6a-/- mice, MF partitioning into SPT and IPT bundles is incomplete and IPT axons in the SO are overextended, while the SPT correctly innervates the SL. Loss of neuronal Sema6a results in defective MF patterning and we show that this involves Sema6A reverse signaling. Plxna4 controls MF partitioning, SPT axon bundling and laminar targeting to the SL, as well as IPT length. Many of these defects are replicated in mice deficient for PlxnA4 GAP catalytic activity, underscoring the importance of this GAP domain. MFs are tightly fasciculated in Plxna2-/- mice and fail to separate into SPT and IPT bundles, and defects are significantly reduced in PlxnA2 GAP mutants, highlighting the involvement of GAP-independent signaling events. To further explore the molecular basis of aberrant axon fasciculation, we employed anti-PlxnA2 dependent proximity biotinylation and identified several PlxnA2-associated Ig-CAM family members. We observed a genetic interaction between Plxna2 and Ncam1, but not Plxna4 and Ncam1, for SPT and IPT formation and positioning in CA3. Together, our studies provide insights into the multifaceted and overlapping, yet distinct, functions of PlxnA family members in orchestrating specific guidance decisions in developing MFs.

developmental biology↗

bioRxiv2024

Sarm1 is not necessary for activation of neuron-intrinsic growth programs yet required for the Schwann cell repair response and peripheral nerve regeneration.

Upon peripheral nervous system (PNS) injury, severed axons undergo rapid SARM1-dependent Wallerian degeneration (WD). In mammals, the role of SARM1 in PNS regeneration, however, is unknown. Here we demonstrate that Sarm1 is not required for axotomy induced activation of neuron-intrinsic growth programs and axonal growth into a nerve crush site. However, in the distal nerve, Sarm1 is necessary for the timely induction of the Schwann cell (SC) repair response, nerve inflammation, myelin clearance, and regeneration of sensory and motor axons. In Sarm1-/- mice, regenerated fibers exhibit reduced axon caliber, defective nerve conduction, and recovery of motor function is delayed. The growth hostile environment of Sarm1-/- distal nerve tissue was demonstrated by grafting of Sarm1-/- nerve into WT recipients. SC lineage tracing in injured WT and Sarm1-/- mice revealed morphological differences. In the Sarm1-/- distal nerve, the appearance of p75NTR+, c-Jun+ SCs is significantly delayed. Ex vivo, p75NTR and c-Jun upregulation in Sarm1-/- nerves can be rescued by pharmacological inhibition of ErbB kinase. Together, our studies show that Sarm1 is not necessary for the activation of neuron intrinsic growth programs but in the distal nerve is required for the orchestration of cellular programs that underlie rapid axon extension.

neuroscience↗

bioRxiv2024

Receptor tyrosine kinases CAD96CA and FGFR1 function as the cell membrane receptors of insect juvenile hormone

Juvenile hormone (JH) is important to maintain insect larval status; however, its cell membrane receptor has not been identified. Using the lepidopteran insect Helicoverpa armigera (cotton bollworm), a serious agricultural pest, as a model, we determined that receptor tyrosine kinases (RTKs) cadherin 96ca (CAD96CA) and fibroblast growth factor receptor homologue (FGFR1) function as JH cell membrane receptors by their roles in JH-regulated gene expression, larval status maintaining, rapid intracellular calcium increase, phosphorylation of JH intracellular receptor MET1 and cofactor Taiman, and high affinity to JH III. Gene knockout of Cad96ca and Fgfr1 by CRISPR/Cas9 in embryo and knockdown in various insect cells, and overexpression of CAD96CA and FGFR1 in mammalian HEK-293T cells all supported CAD96CA and FGFR1 transmitting JH signal as JH cell membrane receptors.

developmental biology↗

bioRxiv2022

The Injured Sciatic Nerve Atlas (iSNAT), Insights into the Cellular and Molecular Basis of Neural Tissue Degeneration and Regeneration

Upon trauma, the adult murine PNS displays a remarkable degree of spontaneous anatomical and functional regeneration. To explore extrinsic mechanisms of neural repair, we carried out single cell analysis of naive mouse sciatic nerve, peripheral blood mononuclear cells, and crushed sciatic nerves at 1-day, 3-days, and 7-days following injury. During the first week, monocytes and macrophages (Mo/Mac) rapidly accumulate in the injured nerve and undergo extensive metabolic reprogramming. Proinflammatory Mo/Mac in the injured nerve show high glycolytic flux compared to Mo/Mac in blood and dominate the early injury response. They subsequently give way to inflammation resolving Mac, programmed toward oxidative phosphorylation. Nerve crush injury causes partial leakiness of the blood-nerve-barrier, proliferation of endoneurial and perineurial stromal cells, and accumulation of select serum proteins. Micro-dissection of the nerve injury site and distal nerve, followed by single-cell RNA-sequencing, identified distinct immune compartments, triggered by mechanical nerve wounding and Wallerian degeneration, respectively. This finding was independently confirmed with Sarm1-/- mice, where Wallerian degeneration is greatly delayed. Experiments with chimeric mice showed that wildtype immune cells readily enter the injury site in Sarm1-/- mice, but are sparse in the distal nerve, except for Mo. We used CellChat to explore intercellular communications in the naive and injured PNS and report on hundreds of ligand-receptor interactions. Our longitudinal analysis represents a new resource for nerve regeneration, reveals location specific immune microenvironments, and reports on large intercellular communication networks. To facilitate mining of scRNAseq datasets, we generated the injured sciatic nerve atlas (iSNAT): https://cdb-rshiny.med.umich.edu/Giger_iSNAT/

neuroscience↗

bioRxiv2021

Plexins Promote Hedgehog Signaling Through Their Cytoplasmic GAP Activity

Hedgehog signaling controls tissue patterning during embryonic and postnatal development and continues to play important roles throughout life. Characterizing the full complement of Hedgehog pathway components is essential to understanding its wide- ranging functions. Previous work has identified Neuropilins, established Semaphorin receptors, as positive regulators of Hedgehog signaling. Neuropilins require Plexin co- receptors to mediate Semaphorin signaling, but a role for Plexins in Hedgehog signaling has not yet been explored. Here, we provide evidence that multiple Plexins promote Hedgehog signaling in NIH/3T3 fibroblasts and that Plexin loss-of-function in these cells results in significantly reduced Hedgehog pathway activity. Catalytic activity of the Plexin GTPase activating protein (GAP) domain is required for Hedgehog signal promotion, and constitutive activation of the GAP domain further amplifies Hedgehog signaling. Additionally, we demonstrate that Plexins promote Hedgehog signaling at the level of GLI transcription factors and that this promotion requires intact primary cilia. Finally, we find that Plexin loss-of-function significantly reduces the response to Hedgehog pathway activation in the mouse dentate gyrus. Together, these data identify Plexins as novel components of the Hedgehog pathway and provide insight into their mechanism of action.

developmental biology↗

bioRxiv2020

Seasonal climate variations promote bacterial α-diversity in soil

Ecological theory suggests that temporal environmental fluctuations can contribute greatly to diversity maintenance. Given bacterias short generation time and rapid responses to environmental change, seasonal climate fluctuations are very likely to play an important role in maintaining the extremely high -diversity of soil bacterial community, which has been unfortunately neglected in previous studies. Here, with in-depth analyses of two previously published soil bacterial datasets at global scale, we found that soil bacterial -diversity was positively correlated with both seasonal variations of temperature and precipitation. Furthermore, piecewise structural equation models showed that seasonal variations of temperature or precipitation directly promoted soil bacterial -diversity in each dataset. However, it is noteworthy that the importance of seasonal climate variations might be underestimated in the above analyses, due to the high level of environmental variations irrelevant to climate seasonality among sampling sites and the lack of sampling across seasons. Supplementary analyses of a previously published wheat cropland dataset with samples collected in both summer and winter across North China Plain was conducted. Similarly, we found that bacterial -diversity was positively correlated with seasonal climate variations, but much stronger, though the range of seasonal climate variations was much smaller compared to the two global datasets. Collectively, these findings implied that fluctuation-dependent mechanisms of diversity maintenance presumably operate in soil bacterial communities. Based on existing evidence, we speculated that the storage effect may be the main mechanism responsible for diversity maintenance in soil bacterial community, but rigorous experimental tests are needed in the future.

ecology↗