Biology subjects

Mitchell, D. M.

Publications and source records attributed to Mitchell, D. M..

4 recordsLinked to original sources

bioRxiv2026

Microglia support regeneration of rod photoreceptors in larval zebrafish retina through Nrf2-independent mechanisms

The molecular and cellular components of successful regeneration of complex tissues in zebrafish are a major area of investigation. Previous work by our lab indicates a redox function for retinal microglia in the first 48 hours following acute injury to rod photoreceptors in the larval zebrafish retina. In addition, recent literature suggests that microglia provide signals that impact the regenerative response in the damaged retina. Here, we investigate the requirement of microglia and the redox-responsive transcription factor Nrf2 in the spontaneous regeneration of rod photoreceptors in the larval zebrafish retina. We used irf8 mutants which are deficient in microglia, and mutant zebrafish lacking a functional copy of the gene nfe2l2a, which encodes a zebrafish ortholog of Nfe2l2/Nrf2. Our results indicate that microglia support the production of regenerated rods following their ablation. However, although detection of reactive oxygen species was increased in nfe2l2a mutant microglia following rod ablation, the regeneration of rods was not impacted in nfe2l2a mutants. Collectively, our results indicate a role for microglia in supporting the production of regenerated retinal neurons while also indicating that Nrf2-independent mechanisms can likely provide redox functions during rod regeneration.

neuroscience↗

bioRxiv2026

Cone photoreceptor ablation in microglia-deficient larval zebrafish retina elicits a regenerative response alongside a compensatory immune cell response

Emerging evidence implicates retinal microglia and inflammation as important components impacting the outcome of retinal regeneration, which is spontaneously achieved in zebrafish retina following acute damage but is limited or blocked in mammals. In this paper, we describe the regenerative response in the larval zebrafish retina following ablation of cone photoreceptors. To investigate the role of microglia in the regenerative response, we used both irf8st95 heterozygote (microglia-sufficient) and irf8st95 homozygous mutant (microglia-deficient) zebrafish. We compared multiple aspects of the regenerative response in irf8+/- and irf8-/- larval retinas, including entry of the Muller glia (MG) into the cell cycle, the amplification of MG-derived progenitor cell (MGPC) proliferation, inflammatory and glial reactivity-associated gene expression, and the regeneration of cones. We found only modest impacts to early and late stages of MGPC proliferation and to inflammatory gene expression in irf8 mutants, with no obvious impacts to the regeneration of cones. Notably, we detected a population of immune cells in irf8 mutants that emerged following cone ablation, which expanded in number then were reduced over time, following a trajectory similar to microglia-sufficient siblings but at markedly reduced abundance. The immune cells detected in irf8 mutants included a subset with L-plastin/4C4 antibody staining patterns different than those in microglia-sufficient siblings, suggesting distinct origins and/or phenotype compared to resident microglia in controls. Though strong conclusions about the role of microglia were limited due to the presence of such immune cell populations in irf8 mutants, our results are consistent with several reports that indicate a role for microglia and inflammation in regulating MGPC proliferation in the regenerating retina. Collectively considered with other reports, our results further indicate that compensatory responses, which may include different immune cells and/or signaling from other retinal cell types such as the Muller glia, are elicited in microglia-deficient retinas upon neuronal damage.

developmental biology↗

bioRxiv2023

Intercellular contact and cargo transfer between Müller glia and to microglia precede apoptotic cell clearance in the developing retina

To clarify our understanding of glial phagocytosis in retinal development, we used real-time imaging of larval zebrafish to provide cell-type specific resolution of this process. We show that radial Muller glia frequently participate in microglial phagocytosis while also completing a subset of phagocytic events. Muller glia (MG) actively engage with dying cells through initial target cell contact and phagocytic cup formation after which an exchange of the dying cell from MG to microglia often takes place. Additionally, we find evidence that Muller glia cellular material, possibly from the initial Muller cells phagocytic cup, is internalized into microglial compartments. Previously undescribed Muller cell behaviors were seen, including cargo splitting, wrestling for targets, lateral passing of cargo to neighbors, and engulfment of what is possibly synaptic puncta. Collectively, our work provides new insight into glial functions and intercellular interactions, which will allow future work to understand these behaviors on a molecular level. Summary StatementReal-time imaging of developing zebrafish retinas reveals intercellular exchanges between Muller glial cells and to microglia during the clearance of apoptotic cells.

developmental biology↗

bioRxiv2020

Microglia in the developing retina couple phagocytosis with the progression of apoptosis via P2RY12 signaling

BackgroundMicroglia colonize the developing vertebrate central nervous system coincident with detection of developmental apoptosis. Our understanding of apoptosis in intact tissue in relation to microglial clearance of dying cells is largely based on fixed samples, which is limiting given that microglia are highly motile and mobile phagocytes. Here, we used a system of microglial depletion and in vivo real-time imaging in zebrafish to directly address microglial phagocytosis of apoptotic cells during normal retinal development, the relative timing of phagocytosis in relation to apoptotic progression, and the contribution of P2RY12 signaling to this process. ResultsDepletion of microglia resulted in accumulation of numerous apoptotic cells in the retina. Real-time imaging revealed precise timing of microglial engulfment with the progression of apoptosis, and dynamic movement and displacement of engulfed apoptotic cells. Inhibition of P2RY12 signaling delayed microglial clearance of apoptotic cells. ConclusionsMicroglial engulfment of dying cells is coincident with apoptotic progression and requires P2RY12 signaling, indicating that microglial P2RY12 signaling is shared between development and injury response. Our work provides important in vivo insight into the dynamics of apoptotic cell clearance in the developing vertebrate retina and provides a basis to understand microglial phagocytic behavior in health and disease. Bullet PointsO_LILevels and location of developmental apoptosis in the zebrafish retina are elusive due to rapid and efficient clearance by microglia C_LIO_LIMicroglial clearance of apoptotic cells is timed with the progression of apoptosis of the engulfed cell so that many cells are cleared in relatively early apoptotic stages C_LIO_LIP2RY12 signaling is involved in microglial sensing and clearance of cells undergoing normal developmental apoptosis, indicating shared signals in microglial responses to cell death in both healthy and injured tissue C_LI Grant SponsorsNIH NIGMS Grant No. P20 GM103408

developmental biology↗