Biology subjects

Robinson, A. N.

Publications and source records attributed to Robinson, A. N..

3 recordsLinked to original sources

bioRxiv2025

The extracellular matrix in selective decussation of retinal ganglion cell axons: β2 laminins regulate the ipsilateral projection

AbstractIn binocular animals, retinal ganglion cell (RGC) axons selectively decussate at the optic chiasm. Selective decussation is directed by radial glia and midline neurons in the optic chiasm. Radial glia attach to the underlying pial basement membrane (PBM) that is rich in {beta}2 laminins. Here, we asked whether {beta}2 laminins in the PBM control the selective decussation of RGC axons. Genetic deletion of the {beta}2 subunit increased the proportion of non-decussating RGC axons in the ipsilateral tract. {beta}2 laminins are expressed in the PBM during the peak and late phases of RGC axon growth, and their deletion results in fragmentation of the PBM and dysmorphic radial glia. Consistent with the increase in the proportion of ipsilateral axons, we found persistent expression of the ipsilateral guidance cue EphrinB2 in radial glia during the late phase of axonal decussation, thus extending the developmental window for the development of the ipsilateral projection. Surprisingly, this increase in EphrinB2 was accompanied by an increase in the number of ipsilateral RGCs in the ventrotemporal retina. These results suggest that {beta}2 laminins regulate the size of the ipsilateral projection by providing cues that control the generation of ipsilateral RGCs and the expression of the ipsilateral cue EphrinB2 in the optic chiasm. Together, these findings position {beta}2 laminins as a novel regulator of the ipsilateral projection.

developmental biology↗

bioRxiv2025

Dynamic fates of dietary antigen-specific T helper cells in a model of early life oral tolerance

Dietary antigens are first encountered in the gut during early life, when the immune system and microbiota are still maturing. In healthy individuals, oral tolerance develops towards dietary antigens: an active process which results in local and systemic immune unresponsiveness to antigens first encountered in the gut. Despite a wealth of research describing mechanisms contributing to oral tolerance in adult rodent models, questions remain about how the early life environment impacts oral tolerance development. We set out to characterize the fate(s) of CD4+ T cells during oral tolerance development using a robust early life mouse model, where controlled oral doses of dietary antigen are given directly to pups during the pre-weaning period. Orally administering 2mg of ovalbumin (OVA) daily during the third week of life was sufficient to confer oral tolerance to OVA in female and male C57BL/6 and BALB/c mice. Following early life oral OVA exposure, a large proportion of OVA-specific CD4+ T cells acquired a Th2 phenotype, alongside some OVA-specific Tregs. Following systemic challenges of OVA with an adjuvant, both OVA-specific Tregs and Th lineage-negative cells expressing anergy markers were detectable in pups given early life oral OVA, while OVA-specific Th2 cells were suppressed in comparison to pups who never received early life oral OVA. These data highlight the diverse fates of CD4+ T cells during early life oral tolerance development and maintenance, and we present a model to study oral tolerance during the early life period when dietary antigens are first encountered.

immunology↗

bioRxiv2021

Characterization and tissue localization of zebrafish homologs of the human ABCB1 multidrug transporter

Given its similarities with mammalian systems, the zebrafish has emerged as a potential model to study the blood-brain barrier (BBB). Capillary endothelial cells at the human BBB express high levels of P-glycoprotein (P-gp, encoded by the ABCB1 gene) and ABCG2 (encoded by the ABCG2 gene). However, little information has been available about ATP-binding cassette transporters expressed at the zebrafish BBB. In this study, we focus on the characterization and tissue localization of two genes that are similar to human ABCB1, zebrafish abcb4 and abcb5. Cytotoxicity assays with stably-transfected cell lines revealed that zebrafish Abcb5 cannot efficiently transport the substrates doxorubicin and mitoxantrone compared to human P-gp and zebrafish Abcb4. Additionally, zebrafish Abcb5 did not transport the fluorescent probes BODIPY-ethylenediamine or LDS 751, while they were readily transported by Abcb4 and P-gp. A high-throughput screen conducted with 90 human P-gp substrates confirmed that zebrafish Abcb4 has overlapping substrate specificity with P-gp. Basal ATPase activity of zebrafish Abcb4 and Abcb5 was comparable to that of human P-gp. In the brain vasculature, RNAscope probes to detect abcb4 colocalized with staining by the P-gp antibody C219, while abcb5 was not detected. Zebrafish abcb4 also colocalized with claudin-5 expression in brain endothelial cells. Abcb4 and Abcb5 had different tissue localizations in multiple zebrafish tissues, consistent with different functions. The data suggest that zebrafish Abcb4 most closely phenocopies P-gp and that the zebrafish may be a viable model to study the role of the multidrug transporter P-gp at the BBB.

pharmacology and toxicology↗