Biology subjects

Mokalled, M.

Publications and source records attributed to Mokalled, M..

4 recordsLinked to original sources

bioRxiv2026

Spinal cord regeneration deploys adult molecular programs that do not recapitulate embryonic development

Adult zebrafish reverse paralysis after spinal cord injury. Their regenerative capacity is stem cell-dependent and often attributed to potent progenitors that retain embryonic radial glial features and reenact developmental programs after injury. To explore the extents to which regeneration recapitulates development, we integrated single-cell RNA-sequencing datasets spanning development, adult homeostasis and adult regeneration. We found immune cell maturation and neuronal differentiation extend into the juvenile stages, while only 25% of injury-responsive adult progenitors recapitulate larval progenitor identities. By annotating larval progenitors based on their dorso-ventral identities and chronological age, we inferred the spatio-temporal features of adult sox2+ progenitors. This analysis showed the dorso-ventral progenitor identities that guide spinal cord development are not faithfully maintained in homeostatic or regenerating adults. This study reports a genome-wide, single-cell examination of similarities and differences between development and regeneration and indicates adult tissue regeneration repurposes developmental pathways into newly acquired regenerative functions rather than recapitulating development.

developmental biology↗

bioRxiv2026

Transient activation of potent progenitor cells is required for spinal cord regeneration

Adult zebrafish exhibit full recovery following spinal cord injury. Transient expansion of stem cell-like progenitors is thought to underlie their regenerative capacity. Yet, our understanding of the identities and contributions of the crucial stem cell populations that direct spontaneous neural repair remains limited. Moreover, while most neural regeneration research is centered on promoting proliferative repair, the regulatory mechanisms that reinstate quiescence post-repair are unknown. Here, we determined the molecular identities and cellular contributions of sox2+ progenitors during spinal cord repair. Genetic lineage tracing shows zebrafish spinal progenitors, while quiescent in uninjured tissues, self-renew and differentiate into neurons and glia after injury. By single-cell sequencing, sox2+ cells are heterogeneous and biased towards neuronal or glial fates in both homeostatic and regenerating tissues. By screening for transcription factors that are differentially expressed in acute versus chronic spinal cord injury, we find the Bach1 transcription factors control transient progenitor cell activation by acting as dual activators and repressors of sox2 expression. This study elucidates the molecular diversity and contributions of sox2 expressing cells during spinal cord repair and identifies a transcriptional regulatory switch by which progenitor cells expand after injury and restore quiescence after regeneration is completed.

neuroscience↗

bioRxiv2025

Hb-EGF directs systemic muscle repair

Regenerative capacity varies between tissues, species, and stages of the life cycle. What is less appreciated is that regenerative capacity also varies with the magnitude of the injury, even within a single tissue. Vertebrate skeletal muscle efficiently regenerates following minor injuries; however, extensive injuries may result in incomplete repair, which can be debilitating. To understand if small- and large-scale muscle injuries activate distinct regenerative programs, we developed a systemic muscle injury model in zebrafish. Transcriptomic analysis of muscle and non-muscle tissues revealed that systemic and local muscle injuries elicit distinct molecular responses, both quantitatively and qualitatively. Systemic muscle injury activated the expression of Heparin binding epidermal-like growth factor (Hb-EGF) in the epidermis, and Hb-EGF is necessary for systemic muscle repair. Conversely, local muscle injury did not induce Hb-EGF expression and Hb-EGF was not required for local muscle repair. These studies suggest that large- and small-scale muscle injuries activate different regenerative programs, resulting in either systemic or local repair.

developmental biology↗

bioRxiv2021

Efficient CRISPR/Cas9 mutagenesis for neurobehavioral screening in adult zebrafish

Adult zebrafish are increasingly used to interrogate mechanisms of disease development and tissue regeneration. Yet, the prospect of large-scale genetics in adult zebrafish has traditionally faced a host of biological and technical challenges. Here, we describe an experimental pipeline that combines high-efficiency CRISPR/Cas9 mutagenesis with functional phenotypic screening to identify genes required for spinal cord repair in adult zebrafish. Using CRISPR/Cas9 dual-guide ribonucleic proteins, we show selective and combinatorial mutagenesis of 17 genes at 28 target sites with efficiencies exceeding 85% in adult F0 crispants. We find that capillary electrophoresis is a reliable method to measure indel frequencies, while avoiding the limitations of restriction enzyme-based genotyping. Using a quantifiable behavioral assay, we identify 7 single- or duplicate-gene crispants with reduced functional recovery after spinal cord injury. To rule out off-target effects, we generate germline mutations that recapitulate the crispant regeneration phenotypes. This study provides a platform that combines high-efficiency somatic mutagenesis with a functional phenotypic readout to perform medium- to large-scale genetic studies in adult zebrafish.

genetics↗