Biology subjects

Saraswathy, V. M.

Publications and source records attributed to Saraswathy, V. M..

4 recordsLinked to original sources

bioRxiv2026

Hapln1-HA signaling promotes progenitor cell proliferation and spinal cord regeneration

Adult zebrafish exhibit scarless repair and functional recovery following spinal cord injury. Their regenerative capacity is attributed to potent stem-like progenitors that mediate neuronal and glial repair. Zebrafish are thought to lack anti-regenerative extracellular matrix (ECM) components abundant in mammalian SCI, but the positive contributions of ECM to spontaneous spinal cord repair are less understood. By employing cross-species single-cell transcriptomics, we found the hyaluran modifying enzyme Hapln1 is upregulated in zebrafish progenitors but not in mouse progenitors following injury. Loss-of-function of hapln1a/b and ablation of hapln1+ cells reduce progenitor cell activation and hinder spontaneous recovery from injury. Using a series of in vivo and in vitro assays, we show that Hapln1 is required for hyaluran-cd44b mediated progenitor cell proliferation. This study reveals that, in addition to lacking anti-regenerative ECM components around SC lesions, zebrafish can also leverage pro-regenerative ECM molecules to enhance progenitor cell potency and promote repair.

neuroscience↗

bioRxiv2024

Elevated phagocytic capacity directs innate spinal cord repair

Immune cells elicit a continuum of transcriptional and functional states after spinal cord injury (SCI). In mammals, inefficient debris clearance and chronic inflammation impede recovery and overshadow pro-regenerative immune functions. We found that, unlike mammals, zebrafish SCI elicits transient immune activation and efficient debris clearance, without causing chronic inflammation. Single-cell transcriptomics and inducible genetic ablation showed zebrafish macrophages are highly phagocytic and required for regeneration. Cross-species comparisons between zebrafish and mammalian macrophages identified transcription and immune response regulator (tcim) as a macrophage-enriched zebrafish gene. Genetic deletion of zebrafish tcim impairs phagocytosis and regeneration, causes aberrant and chronic immune activation, and can be rescued by transplanting wild-type immune precursors into tcim mutants. Conversely, genetic expression of human TCIM accelerates debris clearance and regeneration by reprogramming myeloid precursors into activated phagocytes. This study establishes a central requirement for elevated phagocytic capacity to achieve innate spinal cord repair.

neuroscience↗

bioRxiv2021

The E3 Ubiquitin Ligase Mindbomb1 controls zebrafish Planar Cell Polarity

Vertebrate Delta/Notch signaling involves multiple ligands, receptors and transcription factors. Delta endocytosis - a critical event for Notch activation - is however essentially controlled by the E3 Ubiquitin ligase Mindbomb1 (Mib1). Due to its position at a molecular bottleneck of the pathway, Mib1 inactivation is often used to inhibit Notch signaling. However, recent findings indicate that the importance of Mib1 extends beyond the Notch pathway. We report an essential role of Mib1 in Planar Cell Polarity (PCP). mib1 null mutants or morphants display impaired gastrulation stage Convergence Extension (CE) movements. Comparison of different mib1 mutants and functional rescue experiments indicate that Mib1 controls CE independently of Notch. In contrast, Mib1-dependent CE defects can be rescued using the PCP downstream mediator RhoA. Mib1 regulates CE through the RING Finger domains that have been implicated in substrate ubiquitination, suggesting that Mib1 may control PCP protein trafficking. Accordingly, we show that Mib1 controls the endocytosis of the PCP component Ryk and that Ryk internalization is required for CE. Numerous morphogenetic processes involve both Notch and PCP signaling. We show that Mib1, a known Notch signaling regulator, is also an essential PCP pathway component. Care should therefore be taken when interpreting Mib1 loss of function phenotypes.

developmental biology↗

bioRxiv2019

Delta/Notch signaling controls neuroepithelial morphogenesis in the zebrafish spinal cord

The morphogenesis of the nervous system requires coordinating the specification and differentiation of neural precursor cells, the establishment of neuroepithelial tissue architecture and the execution of specific cellular movements. How these aspects of neural development are linked is incompletely understood. Here we inactivate a major regulator of embryonic neurogenesis - the Delta/Notch pathway - and analyze the effect on zebrafish central nervous system morphogenesis. While some parts of the nervous system can establish neuroepithelial tissue architecture independently of Notch, Notch signaling is essential for spinal cord morphogenesis. In this tissue, Notch signaling is required to repress neuronal differentiation and promote neuroepithelial apico-basal polarity. Concomitant with a loss of their neuroepithelial properties, Notch signaling deficient cells also alter their morphogenetic behavior. In the wild-type zebrafish neural tube, cells divide at the organ midline to contribute one daughter cell to each organ half. Notch deficient animals fail to display this behavior and therefore form a misproportioned spinal cord. Taken together, our findings show that Notch signaling governs not only the cellular composition but also the morphogenetic shaping of the zebrafish spinal cord.

developmental biology↗