Abstract

Spinal cord injury (SCI) causes permanent functional deficits and poses substantial health, economic, and social burdens. Despite extensive efforts, no therapeutic strategy can fully reverse the tissue and functional loss. In contrast to mammals, zebrafish possess a remarkable capacity for spinal cord regeneration and recover locomotor function within 6-8 weeks after injury. Their spontaneous spinal cord repair is characterized by robust proliferation and differentiation of neural progenitors and a permissive extracellular environment that facilitates tissue repair. My dissertation investigates the molecular identities of spinal cord progenitors in the regeneration-competent zebrafish and identifies extracellular matrix (ECM)-driven mechanisms that promote progenitor cell activation following SCI. In the first part of this work, I examined the developmental origin of transcription programs activated during spinal cord regeneration. I integrated single-cell (scRNA-seq) and single-nucleus (snRNA-seq) transcriptomic datasets spanning development, adult homeostasis, and adult post-SCI conditions. These analyses revealed that immune and neuronal cell populations continue to mature beyond larval stages and undergo dynamic changes in both cell type composition and molecular signatures following injury. Adult progenitors were mapped to the developmental dorsoventral (D-V) identities and maturation stages. Adult spinal cord progenitors do not strictly maintain their spatial identities past development. Instead, regeneration involves both the reactivation of developmental programs and the emergence of injury-induced transcriptional states. This study established a transcriptomic comparison framework for understanding how development-recapitulated and injury-responsive mechanisms drive spinal cord regeneration. In the second part of my dissertation, I identified an ECM component that facilitates endogenous spinal cord repair in zebrafish. Hyaluronan and Proteoglycan Link Protein 1 (hapln1) encodes an ECM linker that stabilizes interactions between hyaluronic acid (HA) and proteoglycans. I found that hapln1 is selectively expressed in zebrafish spinal cord progenitors and is upregulated post-SCI, whereas its mammalian ortholog is neither enriched in progenitors nor induced post-SCI. Functional and histological assays revealed that both hapln1-expressing cells and Hapln1-encoding genes are required for swim endurance recovery, axon regrowth, and glial bridge formation during regeneration. In hapln1 stable mutants, progenitor proliferation was significantly reduced after injury, particularly within the HA receptor-positive (cd44b+) progenitor population. The loss of Hapln1 also resulted in decreased hyaluronic acid (HA) deposits in the progenitor niche. Exogenous HA supplementation enhanced progenitor proliferation even in uninjured spinal cords. But HA supplement was not sufficient to rescue the progenitor proliferation defect in hapln1 mutants, indicating that Hapln1-mediated ECM organization is required for HA-driven progenitor activation. This study demonstrated the role of Hapln1-modulated ECM as an evolutionarily concealed mechanism that confers enhanced progenitor response during regeneration. Overall, my thesis work elucidates transcriptional and microenvironmental mechanisms that drive the progenitor response during zebrafish spinal cord regeneration. These findings showed that regeneration deploys both development-recapitulated and injury-responsive programs and identified Hapln1 as a key regulator of progenitor cell activation. Collectively, this dissertation establishes a single-cell comparative framework for understanding endogenous spinal cord repair and highlights an evolutionarily divergent ECM mechanism that may underlie differential regenerative competence.

Committee Chair

Mayssa Mokalled

Committee Members

Aaron DiAntonio

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Molecular Genetics & Genomics)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

8-17-2026

Language

English (en)

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Available for download on Monday, August 14, 2028

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