Cark, O. | bioRxiv Science

bioRxiv2026

Diverse origins and transcriptional profiles of macrophages in a spinal lesion in zebrafish

The injury responses of tissue-resident macrophages in the CNS (microglia) and blood-derived macrophages (BDMs) play key roles in successful regeneration of the zebrafish spinal cord, but the origins and dynamic behaviours of these immune cells are not well characterized. Here, we find that microglia, labelled by the p2ry12:GFP reporter gene, migrate long-distance through neural tissue from the brain to the spinal lesion site, while BDMs, labelled by the mpeg1:mCherry reporter gene, migrate mainly from the caudal hematopoietic tissue to the lesion and back. Half of p2ry12:GFP-positive microglia co-express mpeg1:mCherry, while mpeg1:mCherry-positive BDMs are mostly p2ry12:GFP-negative. However, a BDM sub-population starts to express p2ry12:GFP in the lesion. This indicates heterogeneous and dynamic gene expression in macrophage populations. Gene expression profiling reveals several microglia-like and BDM-like clusters in the lesion with gene expression profiles related to proliferation, phagocytosis, pro- and anti-inflammatory phenotypes and distinct expression of regeneration-relevant genes. The most abundant cell cluster are densely-packed microglia-like cells in the lesion core, which express the novel marker g0s2, as well as phagocytosis-related genes. Hence, regenerative success of the zebrafish spinal cord is linked to a heterogeneous and dynamic response of microglia and BDM subpopulations.

neuroscience↗

bioRxiv2024

Macrophage crosstalk with neural progenitors and fibroblasts controls regenerative neurogenesis via Sema4ab after spinal cord injury in zebrafish

Zebrafish, in contrast to mammals, regenerate neurons after spinal cord injury, but little is known about the control mechanisms of this process. Here we use scRNA-seq and in vivo experiments to show that sema4ab, mainly expressed by lesion-reactive microglia, attenuates regenerative neurogenesis by changing the complex lesion environment. After spinal injury, disruption of sema4ab doubles the number of newly generated progenitor cells and neurons but attenuates axon regrowth and recovery of swimming function. Disruption of the plxnb1a/b receptors, selectively expressed by neural progenitor cells, increases regenerative neurogenesis. In addition, disruption of sema4ab alters activation state and cytokine expression of microglia, such that fibroblasts increase expression of the cytokine tgfb3, which strongly promotes regenerative neurogenesis. Hence, sema4ab in microglia attenuates regenerative neurogenesis in multiple ways, likely directly through plxnb1a/b receptors and indirectly, by controlling the inflammatory milieu and tgfb3 levels. Targeting Sema4A-dependent signalling in non-regenerating vertebrates may be a future strategy to improve regenerative outcomes. HIGHLIGHTS- Microglia suppress pro-regenerative fibroblast signalling in a spinal injury site - Fibroblasts promote regenerative neurogenesis via Tgfb3 signalling - sema4ab promotes microglia activation state after spinal injury - scRNA-seq reveals full complement of sema4ab-dependent changes on different cell types during repair of a spinal lesion site

neuroscience↗